VST (tick elimination) is now available
The first release of the VST package is now available. VST or Variable Scheduling Timeouts (or if you prefer, Variable Sleep Times) contains code that, from the idle task, scans the timer list and, if no timer is near, skips the timer interrupts that would otherwise be generated. The patch name is hrtimers-vst-*
The net result is that a quite system will use far less power as it does not need to wake up ever 1/HZ timer tick.
This patch depends on the high-res-timers patch version hrtimers-2.4.20-3.0 which must be applied first.
Both of these patchs are on sourceforge at:
http://sourceforge.net/projects/high-res-timers/
Some details:
There is a proc directory (/proc/sys/kernel/vst/) dedicated to vst controls. Root may turn VST on or off here with "echo "0">enable. There is also a log option (danger Will Robinson) which, if turned on causes " x" where x is the number of ticks being skipped, to be printed on the log console. This will quickly swamp the console, but it does show things happening during quite times and no such output when the system is busy. It is also possible to set the threshold here. This is in units of milliseconds and is the time the next timer must away from now to trigger a VST sleep. Currently this is set rather large considering that we can sleep only 50ms, but you can change it here.
The file .../include/linux/vst.h contains details on the arch interface. The core code is all in .../kernel/timer.c with enabling bits in various places. The arch code for the x86 version is all located in .../include/asm-i386/hrtime.h
This is, of course, the first cut at this stuff. There is a lot left to do....
Things left to do:
Currently the PIT is used to wake the system for the next timer. If that timer is further away than about 50ms, the PITs limitations force us to use the max PIT time of about 50ms. We plan to use the rtc hardware to do this wake up, thus eliminating this restriction.
SMP imposes further restrictions and, as it currently stands, may cause late timers in some cases. When we port to the 2.6 kernel this will change, for the better, we hope :) This will also allow us to use the APIC timers in these systems to do the wake up, thus allowing longer sleep times.
Signature · 3 lines
George Anzinger [email protected] High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
Hi!
Quoted 8 lines
The first release of the VST package is now available. VST or Variable Scheduling Timeouts (or if you prefer, Variable Sleep Times) contains code that, from the idle task, scans the timer list and, if no timer is near, skips the timer interrupts that would otherwise be generated. The patch name is hrtimers-vst-*
The net result is that a quite system will use far less power as it does not need to wake up ever 1/HZ timer tick.
Do you have some measurements of how much power does it save? Making Sharp Zaurus run longer on batteries would certainly be nice ;-).
Pavel
Signature · 2 lines
When do you have a heart between your knees? [Johanka's followup: and *two* hearts?]
Quoted 11 lines · Pavel Machek
Hi!
Quoted 3 lines
The first release of the VST package is now available. VST or Variable Scheduling Timeouts (or if you prefer, Variable Sleep Times) contains code that, from the idle task, scans the timer list and, if no timer is near, skips the timer interrupts that would otherwise be generated. The patch name is hrtimers-vst-*
The net result is that a quite system will use far less power as it does not need to wake up ever 1/HZ timer tick.
Do you have some measurements of how much power does it save? Making Sharp Zaurus run longer on batteries would certainly be nice ;-).
Pavel
Not just yet. This is a first cut and a good deal of work still needs doing. I could also say that that is why I put it out there :)
Quoted 1 line
Signature · 3 lines
George Anzinger [email protected] High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml