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x86: remove mwait capability C-state check 

Vegard Nossum reports:

| powertop shows between 200-400 wakeups/second with the description
| "<kernel IPI>: Rescheduling interrupts" when all processors have load (e.g.
| I need to run two busy-loops on my 2-CPU system for this to show up).
|
| The bisect resulted in this commit:
|
| commit 0c07ee38c9
| Date:   Wed Jan 30 13:33:16 2008 +0100
|
|     x86: use the correct cpuid method to detect MWAIT support for C states

remove the functional effects of this patch and make mwait unconditional.

A future patch will turn off mwait on specific CPUs where that causes
power to be wasted.

Bisected-by: Vegard Nossum <vegard.nossum@gmail.com>
Tested-by: Vegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2008-05-14 08:47:40 +02:00 committed by Thomas Gleixner
parent f26a398891
commit a738d897b7
1 changed files with 1 additions and 10 deletions
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11
arch/x86/kernel/process.c
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@ -99,15 +99,6 @@ static void mwait_idle(void)
local_irq_enable(); local_irq_enable();
} }
static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
{
if (force_mwait)
return 1;
/* Any C1 states supported? */
return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;
}
/* /*
* On SMP it's slightly faster (but much more power-consuming!) * On SMP it's slightly faster (but much more power-consuming!)
* to poll the ->work.need_resched flag instead of waiting for the * to poll the ->work.need_resched flag instead of waiting for the
@ -131,7 +122,7 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
" performance may degrade.\n"); " performance may degrade.\n");
} }
#endif #endif
if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) { if (cpu_has(c, X86_FEATURE_MWAIT)) {
/* /*
* Skip, if setup has overridden idle. * Skip, if setup has overridden idle.
* One CPU supports mwait => All CPUs supports mwait * One CPU supports mwait => All CPUs supports mwait