linux-kernel - Re: [PATCH] ACPI: do not mark TSC unstable for invalid C-states

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Date:	Mon, 11 May 2009 19:43:17 +0300
From:	Janne Kulmala <janne.t.kulmala@....fi>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Frans Pop <elendil@...net.nl>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>, len.brown@...el.com,
	mingo@...e.hu, johnstul@...ibm.com
Subject: Re: [PATCH] ACPI: do not mark TSC unstable for invalid C-states

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@...utronix.de>
> ---
>  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");;

Small suggestion: can we fix the double ';' here at the same time?

>  #endif
>  		switch (cx->type) {
> 
> 

Janne
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