Commit a738d897 authored May 14, 2008 by Ingo Molnar Committed by Thomas Gleixner May 17, 2008

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 0c07ee38
| 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>

parent f26a3988

arch/x86/kernel/process.c

+1 −10

Original line number	Diff line number	Diff line
		@@ -99,15 +99,6 @@ static void mwait_idle(void)
		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!)
		* 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");
		}
		#endif
		if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
		if (cpu_has(c, X86_FEATURE_MWAIT)) {
		/*
		* Skip, if setup has overridden idle.
		* One CPU supports mwait => All CPUs supports mwait

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