A Dynticks Aware Processor Idle PM Governor

Hi All,

Here is my first take at implementing an idle PM governor that takes full advantage of NO_HZ. I call it the 'menu' governor because it considers the full list of idle states before each entry.

I've kept the implementation fairly simple. It attempts to guess the next residency time and then chooses a state that would meet at least the break-even point between power savings and entry cost. To this end, it selects the deepest idle state that satisfies the following constraints:
1. If the idle time elapsed since bus master activity was detected is below a threshold (currently 20 ms), then limit the selection to C2-type or above.
2. Do not choose a state with a break-even residency that exceeds the expected time remaining until the next timer interrupt.
3. Do not choose a state with a break-even residency that exceeds the elapsed time between the last pair of break events, excluding timer interrupts.

This governor has an advantage over "ladder" governor because it proactively checks how much time remains until the next timer interrupt using the tick infrastructure. Also, it handles device interrupt activity more intelligently by not including timer interrupts in break event calculations. Finally, it doesn't make policy decisions using the number of state entries, which can have variable residency times (NO_HZ makes these potentially very large), and instead only considers sleep time deltas.

The menu governor can be selected during runtime using the cpuidle sysfs interface like so:
"echo "menu" > /sys/devices/system/cpu/cpuidle/current_governor"

This patchset applies against 2.6.21-rc4 plus the latest from the acpi
testing tree, which is available here:
ftp://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/patches/test/2.6.21/acpi-test-20070126-2.6.21-rc4.diff.bz2

I'd really appreciate any comments, benchmarks, or suggestions.

Cheers,
Adam

Applied this series to acpi-test
in anticipation that Venki is about to send some incremental patches to address the feedback on it.

thanks,
-Len

Len,

Following are a bunch of small changes to cpuidle trying to prepare it for mainline. Some of the changes are just the compile timer errors/warnings and you probably already have them in acpi-test.

Should apply cleanly to latest acpi-test. Please include in acpi-test.

Thanks,
Venki

This patch:

cpuidle compile fix related to acpi_set_cstate_limit().

Index: linux-2.6.22-rc-mm/drivers/acpi/osl.c
===================================================================
@@ -1030,6 +1030,7 @@
 	if (acpi_do_set_cstate_limit)
 		acpi_do_set_cstate_limit();
 }
+EXPORT_SYMBOL(acpi_set_cstate_limit);
 
 /*
  * Acquire a spinlock.