linux-kernel - Re: [PATCH 2/2] x86: Enable monitor/mwait on Intel if BIOS hasn't already

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Date:	Wed, 03 Aug 2011 12:15:40 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Andy Lutomirski <luto@....EDU>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Fenghua Yu <fenghua.yu@...el.com>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: Enable monitor/mwait on Intel if BIOS hasn't
 already

On Wed, 3 Aug 2011, Andy Lutomirski wrote:

> I have a Sandy Bridge machine with an Intel BIOS that enables
> monitor/mwait on all but the boot CPU.  With this patch, intel_idle
> works.

What machine has this BIOS bug, and are you running
the latest version of the BIOS?

thanks,
Len Brown, Intel Open Source Technolgy Center

> Signed-off-by: Andy Lutomirski <luto@....edu>
> ---
>  arch/x86/kernel/cpu/intel.c |   20 ++++++++++++++++++++
>  1 files changed, 20 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 6b20fef..a3339a1 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -487,6 +487,26 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
>  			wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
>  		}
>  	}
> +
> +	/* Enable monitor/mwait if BIOS didn't do it for us. */
> +	if (!cpu_has(c, X86_FEATURE_MWAIT) && cpu_has(c, X86_FEATURE_XMM3)
> +	    && c->x86 >= 6 && !(c->x86 == 6 && c->x86_model < 0x1c)
> +	    && !(c->x86 == 0xf && c->x86_model < 3)) {
> +		u64 misc_enable;
> +		rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> +		misc_enable |= MSR_IA32_MISC_ENABLE_MWAIT;
> +
> +		/*
> +		 * Some non-SSE3 cpus will #GP.  We check for that,
> +		 * but it can't hurt to be safe.
> +		 */
> +		wrmsr_safe(MSR_IA32_MISC_ENABLE, (u32)misc_enable,
> +			   (u32)(misc_enable >> 32));
> +
> +		/* Re-read monitor capability. */
> +		if (cpuid_ecx(1) & 0x8)
> +			set_cpu_cap(c, X86_FEATURE_MWAIT);
> +	}
>  }
>  
>  #ifdef CONFIG_X86_32
> -- 
> 1.7.6
> 
> --
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