Hot swap CPU support for 2.4.1

PATCH In review Rusty Russell 5 participants 7 messages Feb 5, 2001 – Feb 11, 2001

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Rusty Russell

author

2001-02-05 04:01 UTC #0 lore raw

PATCH 1/1 Hot swap CPU support for 2.4.1

Hi all,

I did the infrastructure, Anton did the bugfinding and PPC support, aka. the hard stuff. Other architectures need to implement __cpu_disable, __cpu_die and __cpu_up for them to work. Volunteers appreciated.

	This patch allows you to down & up CPUs as follows:
	# echo 0 > /proc/sys/cpu/0/online
	# echo 1 > /proc/sys/cpu/0/online

The relatively trivial patch works as follows:

1) Implements synchronize_kernel() (thanks Andi Kleen for forwarding Paul McKenney's quiescent-state ideas) which waits for a schedule on all CPUs.
2) All CPU numbers are now physical: removes cpu_number_map, cpu_logical_map and smp_num_cpus.
3) Adds cpu_online(cpu) and cpu_num_online() macros.
4) Adds cpu_down() and cpu_up() calls, which call arch-specific __cpu_disable(cpu), __cpu_die(cpu) and __cpu_up(cpu).
5) Fixes schedule() to check allowed_cpus even if rescheduling same task.

Since it's 60k long, mime attached bzip2.

Go hack!
Rusty Russell & Anton Blanchard
--

Lars Marowsky-Bree

2001-02-05 05:52 UTC #1 lore raw

Quoted 4 lines · Rusty Russell

I did the infrastructure, Anton did the bugfinding and PPC support, aka. the hard stuff. Other architectures need to implement __cpu_disable, __cpu_die and __cpu_up for them to work. Volunteers appreciated.

Rusty, what would be needed to "hot-add" CPUs ?

Sincerely,
Lars Marowsky-Brée <[email protected]> SuSE Linux AG at the SAP LinuxLab - [email protected]

Signature · 6 lines

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Anton Blanchard

2001-02-05 06:09 UTC #2 lore raw

In reply to Rusty Russell

Quoted 2 lines

Rusty, what would be needed to "hot-add" CPUs ?

The PPC version at the moment simply locks a cpu in the idle loop with __cli(); while(1); for cpu down and jumps out of it for cpu up. Good for testing but not very useful. After talking to paulus we will use the RTAS cpu stop and cpu start.

In order to bring a new cpu up you will need to duplicate a lot of the stuff in smp_boot_cpus or else just set up all NR_CPUS of these structures (eg NR_CPUS idle threads etc) at boot time.

Anton
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[email protected]

2001-02-05 21:19 UTC #3 lore raw

Re: [PATCH] Hot swap CPU support for 2.4.1@

In reply to Rusty Russell

Would any special hardware besides a multi-cpu system be necessarey to test this out?

Matthew Fredrickson

Quoted 24 lines · Rusty Russell

Hi all,
I did the infrastructure, Anton did the bugfinding and PPC support, aka. the hard stuff. Other architectures need to implement __cpu_disable, __cpu_die and __cpu_up for them to work. Volunteers appreciated.
	This patch allows you to down & up CPUs as follows:
	# echo 0 > /proc/sys/cpu/0/online
	# echo 1 > /proc/sys/cpu/0/online
The relatively trivial patch works as follows:
1) Implements synchronize_kernel() (thanks Andi Kleen for forwarding Paul McKenney's quiescent-state ideas) which waits for a schedule on all CPUs.
2) All CPU numbers are now physical: removes cpu_number_map, cpu_logical_map and smp_num_cpus.
3) Adds cpu_online(cpu) and cpu_num_online() macros.
4) Adds cpu_down() and cpu_up() calls, which call arch-specific __cpu_disable(cpu), __cpu_die(cpu) and __cpu_up(cpu).
5) Fixes schedule() to check allowed_cpus even if rescheduling same task.

Quoted 5 lines

Since it's 60k long, mime attached bzip2.
Go hack!
Rusty Russell & Anton Blanchard
--

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Anton Blanchard

2001-02-06 14:19 UTC #4 lore raw

Re: [PATCH] Hot swap CPU support for 2.4.1@

In reply to Rusty Russell

Quoted 3 lines

Would any special hardware besides a multi-cpu system be necessarey to test this out?

You should be able to run it on any SMP machine assuming you write the arch specific code (PPC could be used as an example). Of course it isn't very interesting if the hardware doesn't support hot swap :)

As soon as I get the SMP ultra booting again (I arrived one morning to hear the disk was making loud grinding noises) I'll code up sparc (ie E10K) support. It sounds like S390 support will be trivial, I'd love to get my hands on one of those :)

Anton
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Pavel Machek

2001-02-11 10:45 UTC #5 lore raw

In reply to Rusty Russell

Hi!

Quoted 11 lines

I did the infrastructure, Anton did the bugfinding and PPC support, aka. the hard stuff. Other architectures need to implement __cpu_disable, __cpu_die and __cpu_up for them to work. Volunteers appreciated.
	This patch allows you to down & up CPUs as follows:
	# echo 0 > /proc/sys/cpu/0/online
	# echo 1 > /proc/sys/cpu/0/online
The relatively trivial patch works as follows:

Quoted 10 lines

1) Implements synchronize_kernel() (thanks Andi Kleen for forwarding Paul McKenney's quiescent-state ideas) which waits for a schedule on all CPUs.
2) All CPU numbers are now physical: removes cpu_number_map, cpu_logical_map and smp_num_cpus.
3) Adds cpu_online(cpu) and cpu_num_online() macros.
4) Adds cpu_down() and cpu_up() calls, which call arch-specific __cpu_disable(cpu), __cpu_die(cpu) and __cpu_up(cpu).
5) Fixes schedule() to check allowed_cpus even if rescheduling same task.

This is not quite right:

@@ -1643,7 +1643,7 @@
printk(KERN_NOTICE "apm: disabled on user

request.\n");
                return -ENODEV;
        }
-       if ((smp_num_cpus > 1) && !power_off) {
+       if ((num_online_cpus() > 1) && !power_off) {
                printk(KERN_NOTICE "apm: disabled - APM is not SMP
safe.\n");
                return -ENODEV;
        }

@@ -1697,7 +1697,7 @@

kernel_thread(apm, NULL, CLONE_FS | CLONE_FILES |
CLONE_SIGHAND | SIGCHLD);

- if (smp_num_cpus > 1) {
+ if (num_online_cpus() > 1) {
printk(KERN_NOTICE
"apm: disabled - APM is not SMP safe (power off

active).\n");
                return 0;

I do not think it is safe to call APM when there is just CPU #5 running. smp_num_cpus in this context means "if we ever had more than boot cpu".
Pavel

Signature · 6 lines

I'm [email protected]. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at [email protected]
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Rusty Russell

author

2001-02-11 23:06 UTC #6 lore raw

In message <[email protected]> you write:

Quoted 11 lines

This is not quite right:

(quoted diff) +1 -1

@@ -1643,7 +1643,7 @@
                printk(KERN_NOTICE "apm: disabled on user
 request.\n");
                return -ENODEV;
        }
-       if ((smp_num_cpus > 1) && !power_off) {
+       if ((num_online_cpus() > 1) && !power_off) {
                printk(KERN_NOTICE "apm: disabled - APM is not SMP

Quoted 3 lines

I do not think it is safe to call APM when there is just CPU #5 running. smp_num_cpus in this context means "if we ever had more than boot cpu".

Um, it's not safe to call APM in SMP full stop: we try anyway. However, this code changes nothing since it's only run at boot.

Cheers,
Rusty.
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Premature optmztion is rt of all evl. --DK
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