Suspend block api (version 8)

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +9 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +9 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:

Quoted 16 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);

Documentation/power/opportunistic-suspend.txt +4 -0

+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

Quoted 16 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);

Documentation/power/opportunistic-suspend.txt +4 -0

+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 17 lines · Arve Hjønnevåg

Quoted 16 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 9 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

That would be very inefficient.

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 17 lines · Arve Hjønnevåg

Quoted 16 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 9 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

That would be very inefficient.

Quoted 28 lines

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 26 lines · Arve Hjønnevåg

Quoted 11 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +9 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 10 lines

Documentation/power/opportunistic-suspend.txt +10 -0

+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

Quoted 1 line

That would be very inefficient.

How so? Anyway, since you admitted this thing isn't needed at all, I say we remove it altogether.

Quoted 28 lines

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 26 lines · Arve Hjønnevåg

Quoted 11 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +9 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 10 lines

Documentation/power/opportunistic-suspend.txt +10 -0

+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

Quoted 1 line

That would be very inefficient.

How so? Anyway, since you admitted this thing isn't needed at all, I say we remove it altogether.

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 17 lines · Arve Hjønnevåg

Quoted 16 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 9 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);

Documentation/power/opportunistic-suspend.txt +4 -0

+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

That would be very inefficient.

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 17 lines · Arve Hjønnevåg

Quoted 16 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 9 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);

Documentation/power/opportunistic-suspend.txt +4 -0

+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

That would be very inefficient.

Quoted 28 lines · On Wed, 26 May 2010 03:47:27 -0700 Arve Hjønnevåg <[email protected]> wrote:

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 26 lines · Arve Hjønnevåg

Quoted 11 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +9 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 10 lines

Documentation/power/opportunistic-suspend.txt +10 -0

+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

Quoted 2 lines

That would be very inefficient.

Also I think it is intended to enforce named suspend blockers. (For debugging/accounting purposes).

Quoted 28 lines · On Wed, 26 May 2010 03:47:27 -0700 Arve Hjønnevåg <[email protected]> wrote:

2010/5/26 Peter Zijlstra <[email protected]>:

Quoted 26 lines · Arve Hjønnevåg

Quoted 11 lines

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +9 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 10 lines

Documentation/power/opportunistic-suspend.txt +10 -0

+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

Quoted 2 lines

That would be very inefficient.

Also I think it is intended to enforce named suspend blockers. (For debugging/accounting purposes).

Quoted 16 lines · Arve Hjønnevåg

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

Quoted 4 lines

This whole thing is related to the statistics part, which Arve says is essential to him.  He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often.  The name also is a part of this.

If he wants to collect stats about misbehaving code then presumably he needs reliable stats. Arbitary user set names are not reliable and judging by app vendor behaviour in the proprietary space with other such examples they will actively name their blockers in a manner specifically intended to hide the cause so as to 'reduce support costs'.

Its a waste of memory (especially if I create a million of them with a long name for fun).

It's all an economic system, proprietary app vendors are in it to make money, some will therefore game the system and the rest will be forced to follow to keep their playing field fair.

desired. The device node interface came about after discussions last year and concerns that userspace could create an unbounded number of suspend blockers.

Quoted 3 lines

It's all an economic system, proprietary app vendors are in it to make money, some will therefore game the system and the rest will be forced to follow to keep their playing field fair.

Untrusted (non-system) code can't directly access the device node from userspace in the Android world -- so directly created suspend blockers

For suspend blockers created by drivers and by trusted userspace processes, having a meaningful name significantly helps statistics gathering.

Quoted 3 lines

desired.  The device node interface came about after discussions last year and concerns that userspace could create an unbounded number of suspend blockers.

Surely you only need one block per task (or better yet one expression of

latency per task). If not can you explain why a setup which has a per task expression of latency needs (and a 'hard limit' set which you can't then bump back down except as root) isn't enough ?

I'd really like this lot to also fix the hard real time and power management problem we have today and to try an fix the "suspend is special and different" mentality in the kernel, which is getting less and less true on a variety of chips.

Quoted 6 lines

Quoted 3 lines

It's all an economic system, proprietary app vendors are in it to make money, some will therefore game the system and the rest will be forced to follow to keep their playing field fair.

Untrusted (non-system) code can't directly access the device node from userspace in the Android world -- so directly created suspend blockers

Great - but the world is not Android and even if they can't access it directly but get passed a handle they can play.

Quoted 3 lines

For suspend blockers created by drivers and by trusted userspace processes, having a meaningful name significantly helps statistics gathering.

By drivers I agree but in the driver case the cost is minimal because there should not be many and it is bounded clearly. Again I really think 'suspend blocking' is the wrong expression.

A driver needs to express

'Don't go below this latency'

and

'Don't go below this state'

This is more generic and helps our power management do the right thing on all boxes. For example a serial port can meaningfully say 'I want X latency worst case' based upon the fact the fifo is 64 bytes and the user space just asked for 115,200 baud.

The don't go below for states out of which the device must wake but cannot. Eg if your device is being told by user space to set wake on lan and can only wake on lan from a higher state than 'off' it needs to say so.

Alan

No, many suspend blockers protect data, not tasks. We block suspend when there are unprocessed input events in the kernel queue. User-space then blocks suspend before reading those events, and it blocks suspend using a different suspend blocker when its queue of processed events become not-empty.

Quoted 4 lines

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

If he wants to collect stats about misbehaving code then presumably he needs reliable stats. Arbitary user set names are not reliable and judging by app vendor behaviour in the proprietary space with other such examples they will actively name their blockers in a manner specifically intended to hide the cause so as to 'reduce support costs'.

Its a waste of memory (especially if I create a million of them with a long name for fun).

It's all an economic system, proprietary app vendors are in it to make money, some will therefore game the system and the rest will be forced to follow to keep their playing field fair.

Quoted 17 lines · Peter Zijlstra

Quoted 16 lines · Arve HjønnevÃ¥g

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 8 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

SET_NAME wouldn't serve any purpose in that case.

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

In fact, without the statistics part the whole thing might be implemented as a single reference counter such that suspend would happen when it went down to zero.

Quoted 17 lines · Peter Zijlstra

Quoted 16 lines · Arve HjønnevÃ¥g

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 8 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

SET_NAME wouldn't serve any purpose in that case.

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

In fact, without the statistics part the whole thing might be implemented as a single reference counter such that suspend would happen when it went down to zero.

Quoted 17 lines · Peter Zijlstra

Quoted 16 lines · Arve HjønnevÃ¥g

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 8 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

SET_NAME wouldn't serve any purpose in that case.

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

In fact, without the statistics part the whole thing might be implemented as a single reference counter such that suspend would happen when it went down to zero.

Quoted 29 lines · Rafael J. Wysocki

Quoted 17 lines · Peter Zijlstra

Quoted 16 lines · Arve HjønnevÃ¥g

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 8 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

SET_NAME wouldn't serve any purpose in that case.

Quoted 8 lines

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

In fact, without the statistics part the whole thing might be implemented as a single reference counter such that suspend would happen when it went down to zero.

There's also Arve's other main point: These suspend blockers tend to get used quite a lot. Opening and closing a file each time has much higher overhead than a simple ioctl.

All these topics have been covered earlier in this discussion. Peter should go back and read the emails in the linux-pm archive.

Quoted 29 lines · Rafael J. Wysocki

Quoted 17 lines · Peter Zijlstra

Quoted 16 lines · Arve HjønnevÃ¥g

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Quoted 8 lines

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

SET_NAME wouldn't serve any purpose in that case.

Quoted 8 lines

This whole thing is related to the statistics part, which Arve says is essential to him. He wants to collect statistics for each suspend blocker activated and deactivated so that he can tell who's causing problems by blocking suspend too often. The name also is a part of this.

In fact, without the statistics part the whole thing might be implemented as a single reference counter such that suspend would happen when it went down to zero.

There's also Arve's other main point: These suspend blockers tend to get used quite a lot. Opening and closing a file each time has much higher overhead than a simple ioctl.

All these topics have been covered earlier in this discussion. Peter should go back and read the emails in the linux-pm archive.

Quoted 16 lines · Arve Hjønnevåg

+To create a suspend blocker from user space, open the suspend_blocker special

Documentation/power/opportunistic-suspend.txt +14 -0

+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+

Documentation/power/opportunistic-suspend.txt if (list_empty(&state->pending_work)) · line 153

Quoted 5 lines

Documentation/power/opportunistic-suspend.txt +5 -0

+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);

Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep the SET_NAME thing if you really care.

The first goal can be achieved either by using device runtime PM and cpuidle to put all hardware into low-power states, transparently from the user space point of view, or by suspending the whole system. However, system suspend, in its current form, does not guarantee that the events of interest will always be responded to, since wakeup events (events that wake the CPU from idle and the system from suspend) that occur right after initiating suspend will not be processed until another possibly unrelated event wakes the system up again.

The first goal can be achieved either by using device runtime PM and cpuidle to put all hardware into low-power states, transparently from the user space point of view, or by suspending the whole system. However, system suspend, in its current form, does not guarantee that the events of interest will always be responded to, since wakeup events (events that wake the CPU from idle and the system from suspend) that occur right after initiating suspend will not be processed until another possibly unrelated event wakes the system up again.

Quoted 10 lines

The first goal can be achieved either by using device runtime PM and cpuidle to put all hardware into low-power states, transparently from the user space point of view, or by suspending the whole system. However, system suspend, in its current form, does not guarantee that the events of interest will always be responded to, since wakeup events (events that wake the CPU from idle and the system from suspend) that occur right after initiating suspend will not be processed until another possibly unrelated event wakes the system up again.

Minor point of clarification here.  I'm not requesting that the patch description be rewritten.  But this issue of lost wakeup events is more subtle than it appears.

Wakeup events can be lost in at least three different ways:

    1. A hardware signal (such as an IRQ) gets ignored.

    2. The hardware event occurs, but without effect since the kernel thread that would handle the event has been frozen. The event just ends up sitting in a queue somewhere until something else wakes up the system.

    3. The hardware event occurs and the kernel handles it fully, but the event propagates to userspace for further handling and the user program is already frozen.

1 is a hardware configuration failure (for example, it might happen as a result of using edge-triggered IRQs instead of level-triggered) and is outside the scope of this discussion.

2 generally represents a failure of the core PM subsystem, or a failure of some other part of the kernel to use the PM core correctly.  In theory we should be able to fix such mistakes.  Right now I'm aware of at least one possible failure scenario that could be fixed fairly easily.

3 is the type of failure that suspend blockers were really meant to handle, particularly the userspace suspend-blocker API.

IMO, we should strive to fix the existing type-2 failure modes. However it is worth pointing out that they are basically separate from the suspend-blocker mechanism.

And it might be a good idea to point out somewhere in the patch descriptions that suspend blockers are really meant to handle type-3 wakeup losses.

Quoted 10 lines

The first goal can be achieved either by using device runtime PM and cpuidle to put all hardware into low-power states, transparently from the user space point of view, or by suspending the whole system. However, system suspend, in its current form, does not guarantee that the events of interest will always be responded to, since wakeup events (events that wake the CPU from idle and the system from suspend) that occur right after initiating suspend will not be processed until another possibly unrelated event wakes the system up again.

Minor point of clarification here.  I'm not requesting that the patch description be rewritten.  But this issue of lost wakeup events is more subtle than it appears.

Wakeup events can be lost in at least three different ways:

    1. A hardware signal (such as an IRQ) gets ignored.

    2. The hardware event occurs, but without effect since the kernel thread that would handle the event has been frozen. The event just ends up sitting in a queue somewhere until something else wakes up the system.

    3. The hardware event occurs and the kernel handles it fully, but the event propagates to userspace for further handling and the user program is already frozen.

1 is a hardware configuration failure (for example, it might happen as a result of using edge-triggered IRQs instead of level-triggered) and is outside the scope of this discussion.

2 generally represents a failure of the core PM subsystem, or a failure of some other part of the kernel to use the PM core correctly.  In theory we should be able to fix such mistakes.  Right now I'm aware of at least one possible failure scenario that could be fixed fairly easily.

3 is the type of failure that suspend blockers were really meant to handle, particularly the userspace suspend-blocker API.

IMO, we should strive to fix the existing type-2 failure modes. However it is worth pointing out that they are basically separate from the suspend-blocker mechanism.

And it might be a good idea to point out somewhere in the patch descriptions that suspend blockers are really meant to handle type-3 wakeup losses.

Quoted 23 lines

Wakeup events can be lost in at least three different ways:

    1. A hardware signal (such as an IRQ) gets ignored.

    2. The hardware event occurs, but without effect since the kernel thread that would handle the event has been frozen. The event just ends up sitting in a queue somewhere until something else wakes up the system.

    3. The hardware event occurs and the kernel handles it fully, but the event propagates to userspace for further handling and the user program is already frozen.

1 is a hardware configuration failure (for example, it might happen as a result of using edge-triggered IRQs instead of level-triggered) and is outside the scope of this discussion.

2 generally represents a failure of the core PM subsystem, or a failure of some other part of the kernel to use the PM core correctly.  In theory we should be able to fix such mistakes.  Right now I'm aware of at least one possible failure scenario that could be fixed fairly easily.

Quoted 2 lines

3 is the type of failure that suspend blockers were really meant to handle, particularly the userspace suspend-blocker API.

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

Quoted 23 lines

Wakeup events can be lost in at least three different ways:

    1. A hardware signal (such as an IRQ) gets ignored.

    2. The hardware event occurs, but without effect since the kernel thread that would handle the event has been frozen. The event just ends up sitting in a queue somewhere until something else wakes up the system.

    3. The hardware event occurs and the kernel handles it fully, but the event propagates to userspace for further handling and the user program is already frozen.

1 is a hardware configuration failure (for example, it might happen as a result of using edge-triggered IRQs instead of level-triggered) and is outside the scope of this discussion.

2 generally represents a failure of the core PM subsystem, or a failure of some other part of the kernel to use the PM core correctly.  In theory we should be able to fix such mistakes.  Right now I'm aware of at least one possible failure scenario that could be fixed fairly easily.

Quoted 2 lines

3 is the type of failure that suspend blockers were really meant to handle, particularly the userspace suspend-blocker API.

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

Quoted 23 lines · Arve Hjønnevåg

Quoted 23 lines

Wakeup events can be lost in at least three different ways:

    1. A hardware signal (such as an IRQ) gets ignored.

    2. The hardware event occurs, but without effect since the kernel thread that would handle the event has been frozen. The event just ends up sitting in a queue somewhere until something else wakes up the system.

    3. The hardware event occurs and the kernel handles it fully, but the event propagates to userspace for further handling and the user program is already frozen.

1 is a hardware configuration failure (for example, it might happen as a result of using edge-triggered IRQs instead of level-triggered) and is outside the scope of this discussion.

2 generally represents a failure of the core PM subsystem, or a failure of some other part of the kernel to use the PM core correctly.  In theory we should be able to fix such mistakes.  Right now I'm aware of at least one possible failure scenario that could be fixed fairly easily.

Quoted 5 lines

Quoted 2 lines

3 is the type of failure that suspend blockers were really meant to handle, particularly the userspace suspend-blocker API.

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

You can, but they aren't necessary. If 2 were the only reason for suspend blockers, I would say they shouldn't be merged.

Whereas 3, on the other hand, can _not_ be handled by any existing mechanism. 3 is perhaps the most important reason for using suspend blockers.

Quoted 23 lines · Arve Hjønnevåg

Quoted 23 lines

Wakeup events can be lost in at least three different ways:

    1. A hardware signal (such as an IRQ) gets ignored.

    2. The hardware event occurs, but without effect since the kernel thread that would handle the event has been frozen. The event just ends up sitting in a queue somewhere until something else wakes up the system.

    3. The hardware event occurs and the kernel handles it fully, but the event propagates to userspace for further handling and the user program is already frozen.

1 is a hardware configuration failure (for example, it might happen as a result of using edge-triggered IRQs instead of level-triggered) and is outside the scope of this discussion.

2 generally represents a failure of the core PM subsystem, or a failure of some other part of the kernel to use the PM core correctly.  In theory we should be able to fix such mistakes.  Right now I'm aware of at least one possible failure scenario that could be fixed fairly easily.

Quoted 5 lines

Quoted 2 lines

3 is the type of failure that suspend blockers were really meant to handle, particularly the userspace suspend-blocker API.

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

You can, but they aren't necessary. If 2 were the only reason for suspend blockers, I would say they shouldn't be merged.

Whereas 3, on the other hand, can _not_ be handled by any existing mechanism. 3 is perhaps the most important reason for using suspend blockers.

Quoted 10 lines

Quoted 2 lines

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

You can, but they aren't necessary. If 2 were the only reason for suspend blockers, I would say they shouldn't be merged.

Whereas 3, on the other hand, can _not_ be handled by any existing mechanism. 3 is perhaps the most important reason for using suspend blockers.

I do not see why 3 has to be implemented using suspend blockers either. If you are concerned that event gets stuck somewhere in the stack make sure that devices in the stack do not suspend while their queue is not empty. This way if you try opportunistic suspend it will keep failing until you drained all important queues.

Quoted 10 lines

Quoted 2 lines

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

You can, but they aren't necessary. If 2 were the only reason for suspend blockers, I would say they shouldn't be merged.

Whereas 3, on the other hand, can _not_ be handled by any existing mechanism. 3 is perhaps the most important reason for using suspend blockers.

I do not see why 3 has to be implemented using suspend blockers either. If you are concerned that event gets stuck somewhere in the stack make sure that devices in the stack do not suspend while their queue is not empty. This way if you try opportunistic suspend it will keep failing until you drained all important queues.

Quoted 10 lines · Dmitry Torokhov

Quoted 9 lines

Quoted 2 lines

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

You can, but they aren't necessary. If 2 were the only reason for suspend blockers, I would say they shouldn't be merged.

Whereas 3, on the other hand, can _not_ be handled by any existing mechanism. 3 is perhaps the most important reason for using suspend blockers.

Quoted 5 lines

I do not see why 3 has to be implemented using suspend blockers either. If you are concerned that event gets stuck somewhere in the stack make sure that devices in the stack do not suspend while their queue is not empty. This way if you try opportunistic suspend it will keep failing until you drained all important queues.

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue. A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it. As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read. As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario. Here's how:

The user process doesn't read the input queue directly; instead it does a select or poll. When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active. The user process can do whatever it wants with the keystroke. When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 10 lines · Dmitry Torokhov

Quoted 9 lines

Quoted 2 lines

I don't see a big difference between 2 and 3. You can use suspend blockers to handle either.

You can, but they aren't necessary. If 2 were the only reason for suspend blockers, I would say they shouldn't be merged.

Whereas 3, on the other hand, can _not_ be handled by any existing mechanism. 3 is perhaps the most important reason for using suspend blockers.

Quoted 5 lines

I do not see why 3 has to be implemented using suspend blockers either. If you are concerned that event gets stuck somewhere in the stack make sure that devices in the stack do not suspend while their queue is not empty. This way if you try opportunistic suspend it will keep failing until you drained all important queues.

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue. A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it. As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read. As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario. Here's how:

The user process doesn't read the input queue directly; instead it does a select or poll. When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active. The user process can do whatever it wants with the keystroke. When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue. A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it. As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read. As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario. Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll. When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active. The user process can do whatever it wants with the keystroke. When it is finished, it releases the suspend blocker and loops back to the select/poll call.

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue. A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it. As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read. As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario. Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll. When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active. The user process can do whatever it wants with the keystroke. When it is finished, it releases the suspend blocker and loops back to the select/poll call.

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue. A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it. As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read. As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario. Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll. When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active. The user process can do whatever it wants with the keystroke. When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work. And it might remove the need for the userspace suspend-blocker API, which would be an advantage. It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty. Doing that is more or less equivalent to implementing kernel-level suspend blockers. (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Maybe I'm missing something here... No doubt someone will point it out if I am.

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue. A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it. As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read. As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario. Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll. When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active. The user process can do whatever it wants with the keystroke. When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work. And it might remove the need for the userspace suspend-blocker API, which would be an advantage. It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty. Doing that is more or less equivalent to implementing kernel-level suspend blockers. (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Maybe I'm missing something here... No doubt someone will point it out if I am.

Quoted 21 lines

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work. And it might remove the need for the userspace suspend-blocker API, which would be an advantage. It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty. Doing that is more or less equivalent to implementing kernel-level suspend blockers. (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here... No doubt someone will point it out if I am.

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 21 lines

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work. And it might remove the need for the userspace suspend-blocker API, which would be an advantage. It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty. Doing that is more or less equivalent to implementing kernel-level suspend blockers. (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here... No doubt someone will point it out if I am.

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

Quoted 82 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

Quoted 82 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 90 lines · Arve Hjønnevåg

Quoted 82 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

Quoted 3 lines

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

or releases the
currently held key.

Quoted 4 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

Quoted 4 lines

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

That does not sound right.

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 90 lines · Arve Hjønnevåg

Quoted 82 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

Quoted 3 lines

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

or releases the
currently held key.

Quoted 4 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

Quoted 4 lines

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

That does not sound right.

Quoted 95 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 93 lines · Arve Hjønnevåg

Quoted 82 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

Quoted 3 lines

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

Employ reasonable timeout.

Quoted 4 lines

or releases the
currently held key.

Userspace consumer should wait for the key release and retract "busy" once event is received and handled.

Quoted 9 lines

Quoted 8 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Quoted 3 lines

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Why would a driver, on its own, prevent suspend for extended periods of time? I think that the decision should originate from userspace, kernel is here just to serve the requests.

Quoted 7 lines

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

Quoted 1 line

That does not sound right.

Why doesn't it? If a device implements runtime PM it may chose remain in powered-down mode even if system is awake.

Quoted 95 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 93 lines · Arve Hjønnevåg

Quoted 82 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 74 lines · Arve Hjønnevåg

Quoted 65 lines

Quoted 53 lines · Dmitry Torokhov

Quoted 48 lines · Alan Stern

Quoted 25 lines · Dmitry Torokhov

Quoted 15 lines

Here's the scenario:

The system is awake, and the user presses a key. The keyboard driver processes the keystroke and puts it in an input queue.  A user process reads it from the event queue, thereby emptying the queue.

At that moment, the system decides to go into opportunistic suspend. Since the input queue is empty, there's nothing to stop it.  As the first step, userspace is frozen -- before the process has a chance to do anything with the keystroke it just read.  As a result, the system stays asleep until something else wakes it up, even though the keystroke was important and should have prevented it from sleeping.

Suspend blockers protect against this scenario.  Here's how:

Quoted 9 lines

The user process doesn't read the input queue directly; instead it does a select or poll.  When it sees there is data in the queue, it first acquires a suspend blocker and then reads the data.

Now the system _can't_ go into opportunistic suspend, because a suspend blocker is active.  The user process can do whatever it wants with the keystroke.  When it is finished, it releases the suspend blocker and loops back to the select/poll call.

Quoted 6 lines

What you describe can be done in userspace though, via a "suspend manager" process. Tasks reading input events will post "busy" events to stop the manager process from sending system into suspend. But this can be confined to Android userspace, leaving the kernel as is (well, kernel needs to be modified to not go into suspend with full queues, but that is using existing kernel APIs).

I think that could be made to work.  And it might remove the need for the userspace suspend-blocker API, which would be an advantage.  It could even remove the need for the opportunistic-suspend workqueue -- opportunistic suspends would be initiated by the "suspend manager" process instead of by the kernel.

However you still have the issue of modifying the kernel drivers to disallow opportunistic suspend if their queues are non-empty.  Doing that is more or less equivalent to implementing kernel-level suspend blockers.  (The suspend blocker approach is slightly more efficient, because it will prevent a suspend from starting if a queue is non-empty, instead of allowing the suspend to start and then aborting it partway through.)

Quoted 3 lines

Maybe I'm missing something here...  No doubt someone will point it out if I am.

Quoted 9 lines

Well, from my perspective that would limit changes to the evdev driver (well, limited input core plumbing will be needed) but that is using the current PM infrastructure. The HW driver changes will be limited to what you described "type 2" in your other e-mail.

Also, not suspending while events are in progress) is probably beneficial for platforms other than Android as well. So unless I am missing something this sounds like a win.

Quoted 7 lines

How would this limit the changes you need in the evdev driver? It need to block suspend when there are unprocessed events in some queues. Suspend blockers gives you an api to do this, without it, you check the queues in your suspend hook and abort suspend if they are not empty. Without suspend blockers you have no api to signal that it is OK to suspend again, so you are forcing the thread that tried to suspend to poll until you stop aborting suspend.

Quoted 6 lines

No, you do not need to poll. You just set a timeout (short or long, depending on your needs) and if no userspace task blocked suspend durng that time you attempt to initiate suspend from your manager process. If it succeeds - good, if not that means that more events came your way and you have to do it later.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

Quoted 3 lines

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

Employ reasonable timeout.

Quoted 4 lines

or releases the
currently held key.

Userspace consumer should wait for the key release and retract "busy" once event is received and handled.

Quoted 9 lines

Quoted 8 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Quoted 3 lines

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Why would a driver, on its own, prevent suspend for extended periods of time? I think that the decision should originate from userspace, kernel is here just to serve the requests.

Quoted 7 lines

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

Quoted 1 line

That does not sound right.

Why doesn't it? If a device implements runtime PM it may chose remain in powered-down mode even if system is awake.

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 7 lines · Arve Hjønnevåg

Quoted 4 lines

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

Employ reasonable timeout.

Timeout for what? Stop trying to suspend altogether, stop scanning for key changes, or a more "reasonable" poll interval?

Quoted 6 lines

Quoted 5 lines

or releases the
currently held key.

Quoted 3 lines

Userspace consumer should wait for the key release and retract "busy" once event is received and handled.

No it should not. User-space does not know if the key is coming from a keypad driver that needs to actively scan the matrix while keys are pressed.

Quoted 10 lines

Quoted 10 lines

Quoted 9 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Quoted 8 lines

Quoted 3 lines

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Why would a driver, on its own, prevent suspend for extended periods of time? I think that the decision should originate from userspace, kernel is here just to serve the requests.

A driver prevents suspend if suspend would prevent it from working. For instance, the gpio keypad matrix code prevents suspend when a key is help down, since it has to activly scan the keypad for changes. Only no-keys-pressed versus one-or-more-keys-pressed can be detected with an interrupt.

Quoted 7 lines

Quoted 7 lines

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

Quoted 5 lines

Quoted 1 line

That does not sound right.

Why doesn't it? If a device implements runtime PM it may chose remain in powered-down mode even if system is awake.

If the device implements runtime PM it should already be powered-down if it is not in use.

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 7 lines · Arve Hjønnevåg

Quoted 4 lines

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

Employ reasonable timeout.

Timeout for what? Stop trying to suspend altogether, stop scanning for key changes, or a more "reasonable" poll interval?

Quoted 6 lines

Quoted 5 lines

or releases the
currently held key.

Quoted 3 lines

Userspace consumer should wait for the key release and retract "busy" once event is received and handled.

No it should not. User-space does not know if the key is coming from a keypad driver that needs to actively scan the matrix while keys are pressed.

Quoted 10 lines

Quoted 10 lines

Quoted 9 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Quoted 8 lines

Quoted 3 lines

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Why would a driver, on its own, prevent suspend for extended periods of time? I think that the decision should originate from userspace, kernel is here just to serve the requests.

A driver prevents suspend if suspend would prevent it from working. For instance, the gpio keypad matrix code prevents suspend when a key is help down, since it has to activly scan the keypad for changes. Only no-keys-pressed versus one-or-more-keys-pressed can be detected with an interrupt.

Quoted 7 lines

Quoted 7 lines

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

Quoted 5 lines

Quoted 1 line

That does not sound right.

Why doesn't it? If a device implements runtime PM it may chose remain in powered-down mode even if system is awake.

If the device implements runtime PM it should already be powered-down if it is not in use.

Quoted 7 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 6 lines · Arve Hjønnevåg

Quoted 4 lines

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

Quoted 4 lines

Quoted 1 line

Employ reasonable timeout.

Timeout for what? Stop trying to suspend altogether, stop scanning for key changes, or a more "reasonable" poll interval?

Stop trying to suspend for a fraction of a second to see if user wants to press another key.

Quoted 10 lines

Quoted 9 lines

Quoted 5 lines

or releases the
currently held key.

Userspace consumer should wait for the key release and retract "busy" once event is received and handled.

Quoted 3 lines

No it should not. User-space does not know if the key is coming from a keypad driver that needs to actively scan the matrix while keys are pressed.

OTOH nor does kernel driver know whether system suspend should be blocked while it is scanning.

What should happen in I press KEY_SUSPEND?
Do we always want to wait till user releases it?

Quoted 39 lines

Quoted 11 lines

Quoted 11 lines

Quoted 10 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Quoted 8 lines

Quoted 3 lines

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Why would a driver, on its own, prevent suspend for extended periods of time? I think that the decision should originate from userspace, kernel is here just to serve the requests.

A driver prevents suspend if suspend would prevent it from working. For instance, the gpio keypad matrix code prevents suspend when a key is help down, since it has to activly scan the keypad for changes. Only no-keys-pressed versus one-or-more-keys-pressed can be detected with an interrupt.

Quoted 12 lines

Quoted 8 lines

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

That does not sound right.

Why doesn't it? If a device implements runtime PM it may chose remain in powered-down mode even if system is awake.

Quoted 2 lines

If the device implements runtime PM it should already be powered-down if it is not in use.

It could have been in use but userspace-initiated suspend accelerated it entering low power state.

Quoted 7 lines

2010/5/25 Dmitry Torokhov <[email protected]>:

Quoted 6 lines · Arve Hjønnevåg

Quoted 4 lines

You are missing the point. There are no event pending. The kernel reported the key down event, it was handled, but the keypad driver is still scanning to see if the user presses another key,

Quoted 4 lines

Quoted 1 line

Employ reasonable timeout.

Timeout for what? Stop trying to suspend altogether, stop scanning for key changes, or a more "reasonable" poll interval?

Stop trying to suspend for a fraction of a second to see if user wants to press another key.

Quoted 10 lines

Quoted 9 lines

Quoted 5 lines

or releases the
currently held key.

Userspace consumer should wait for the key release and retract "busy" once event is received and handled.

Quoted 3 lines

No it should not. User-space does not know if the key is coming from a keypad driver that needs to actively scan the matrix while keys are pressed.

OTOH nor does kernel driver know whether system suspend should be blocked while it is scanning.

What should happen in I press KEY_SUSPEND?
Do we always want to wait till user releases it?

Quoted 39 lines

Quoted 11 lines

Quoted 11 lines

Quoted 10 lines

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Quoted 8 lines

Quoted 3 lines

No, the difference is that if a driver needs to prevent suspend for an extended period of time, you don't have user space continuously polling to see if it can suspend.

Why would a driver, on its own, prevent suspend for extended periods of time? I think that the decision should originate from userspace, kernel is here just to serve the requests.

A driver prevents suspend if suspend would prevent it from working. For instance, the gpio keypad matrix code prevents suspend when a key is help down, since it has to activly scan the keypad for changes. Only no-keys-pressed versus one-or-more-keys-pressed can be detected with an interrupt.

Quoted 12 lines

Quoted 8 lines

Quoted 6 lines

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

That does not sound right.

Why doesn't it? If a device implements runtime PM it may chose remain in powered-down mode even if system is awake.

Quoted 2 lines

If the device implements runtime PM it should already be powered-down if it is not in use.

It could have been in use but userspace-initiated suspend accelerated it entering low power state.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.

Quoted 4 lines

How is that not polling? If the user is holding down a key, the keypad driver has to block suspend, and user space will try to suspend again and again and again...

If your userpsace is that stupid - sure. However, you can:

1. Notify the suspend manager process that he rest of your userspace is busy handling keystrokes so that it does not try to suspend while there are events pending.

2. Wait a tiny bit after last application notified you that it finished processing events.

So basically the difference is that with in-kernel suspend blockers, there is a tiny window where we haven't started the suspend yet but are about to the driver has a chance to prevent entire system from starting sleep.

Without the blocker we may start suspending and will stop midcycle. We may be even better off in the end since we could leave some devices still powered down after aborting system-wide suspend.