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Date: Thu, 3 Jan 2008 11:45:26 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Andi Kleen <ak@suse.de>
Cc: andreas.herrmann3@amd.com, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] [11/20] x86: Use the correct cpuid method to detect
	MWAIT support for C states
Message-ID: <20080103104526.GC29194@elte.hu>
References: <20080103149.088038000@suse.de> <20080103005006.BE79A14D40@wotan.suse.de>
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* 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