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DateThu, 3 Jan 2008 11:45:26 +0100
FromIngo Molnar <>
SubjectRe: [PATCH] [11/20] x86: Use the correct cpuid method to detect MWAIT support for C states
* Andi Kleen <ak@suse.de> wrote:

> +static int 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;
> +}
> +
>  void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
>  {
> -	if (cpu_has(c, X86_FEATURE_MWAIT)) {
> +	if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
>  		printk("monitor/mwait feature present.\n");

hm, why not clear FEATURE_MWAIT if it's "not usable"? That's the 
standard approach we do for CPU features that do not work.

	Ingo


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