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Date: Mon, 11 May 2009 11:00:19 -0400 (EDT)
From: Steven Rostedt <rostedt@goodmis.org>
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To: Thomas Gleixner <tglx@linutronix.de>
cc: Frans Pop <elendil@planet.nl>, linux-kernel@vger.kernel.org,
       len.brown@intel.com, mingo@elte.hu, johnstul@us.ibm.com
Subject: Re: [PATCH] ACPI: do not mark TSC unstable for invalid C-states
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On Mon, 11 May 2009, Thomas Gleixner wrote:

> commit a71e4917dc0ebbcb5a0ecb7ca3486643c1c9a6e2 (ACPI: idle:
> mark_tsc_unstable() at init-time, not run-time) marks TSC unstable
> even on non affected systems.
> 
> The reason is that the state enumeration does not check the cx->valid
> flag before calling tsc_halts_in_c(), so it marks TSC unstable for any
> enumerated albeit invalid C state which is known to turn off TSC.
> 
> Check cx->valid before checking whether the TSC might become unstable.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Tested-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

> ---
>  drivers/acpi/processor_idle.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/drivers/acpi/processor_idle.c
> ===================================================================
> --- linux-2.6.orig/drivers/acpi/processor_idle.c
> +++ linux-2.6/drivers/acpi/processor_idle.c
> @@ -583,7 +583,7 @@ static int acpi_processor_power_verify(s
>  
>  #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
>  		/* TSC could halt in idle, so notify users */
> -		if (tsc_halts_in_c(cx->type))
> +		if (cx->valid && tsc_halts_in_c(cx->type))
>  			mark_tsc_unstable("TSC halts in idle");;
>  #endif
>  		switch (cx->type) {
> 
> 
>