linux-kernel - Re: [PATCH] ACPI: Idle C-states disabled by max

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Date:	Fri, 15 May 2009 10:27:55 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Len Brown <lenb@...nel.org>
cc:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Janne Kulmala <janne.t.kulmala@....fi>,
	Frans Pop <elendil@...net.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>, johnstul@...ibm.com,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH] ACPI: Idle C-states disabled by max_cstate should not
 disable the TSC

On Fri, 15 May 2009, Len Brown wrote:

> From: Len Brown <len.brown@...el.com>
> 
> Processor idle power states C2 and C3 stop the TSC on many machines.
> Linux recognizes this situation and marks the TSC as unstable:
> 
> Marking TSC unstable due to TSC halts in idle
> 
> But if those same machines are booted with "processor.max_cstate=1",
> then there is no need to validate C2 and C3, and no need to
> disable the TSC, which can be reliably used as a clocksource.
> 
> Signed-off-by: Len Brown <len.brown@...el.com>

Acked-by: Thomas Gleixner <tglx@...utronix.de>

> ---
>  drivers/acpi/processor_idle.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index e39a40a..e65476f 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -582,7 +582,7 @@ static int acpi_processor_power_verify(struct acpi_processor *pr)
>  
>  	pr->power.timer_broadcast_on_state = INT_MAX;
>  
> -	for (i = 1; i < ACPI_PROCESSOR_MAX_POWER; i++) {
> +	for (i = 1; i < ACPI_PROCESSOR_MAX_POWER && i <= max_cstate; i++) {
>  		struct acpi_processor_cx *cx = &pr->power.states[i];
>  
>  		switch (cx->type) {
> -- 
> 1.6.3.1.9.g95405b
> 
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