linux-kernel - Re: [tip:timers/urgent] NOHZ: Properly feed cpufreq ondemand governor

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Date:	Wed, 27 May 2009 09:23:56 -0400
From:	Rik van Riel <riel@...hat.com>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	tero.kristo@...ia.com, ext-eero.nurkkala@...ia.com,
	venkatesh.pallipadi@...el.com, tglx@...utronix.de
Subject: Re: [tip:timers/urgent] NOHZ: Properly feed cpufreq ondemand governor

tip-bot for Eero Nurkkala wrote:
> Commit-ID:  cf1240033cc81216a18eec0ca71466f7fe4eeda8
> Gitweb:     http://git.kernel.org/tip/cf1240033cc81216a18eec0ca71466f7fe4eeda8
> Author:     Eero Nurkkala <ext-eero.nurkkala@...ia.com>
> AuthorDate: Mon, 25 May 2009 09:57:37 +0300
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Wed, 27 May 2009 14:51:47 +0200
> 
> NOHZ: Properly feed cpufreq ondemand governor
> 
> A call from irq_exit() may occasionally pause the timing
> info for cpufreq ondemand governor. This results in the
> cpufreq ondemand governor to fail to calculate the
> system load properly. Thus, relocate the checks for this
> particular case to keep the governor always functional.
> 
> Signed-off-by: Eero Nurkkala <ext-eero.nurkkala@...ia.com>
> Reported-by: Tero Kristo <tero.kristo@...ia.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
> LKML-Reference: <12432346571351-git-send-email-ext-eero.nurkkala@...ia.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> 
> ---
>  kernel/time/tick-sched.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index d3f1ef4..233b4e7 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -222,6 +222,15 @@ void tick_nohz_stop_sched_tick(int inidle)
>  
>  	cpu = smp_processor_id();
>  	ts = &per_cpu(tick_cpu_sched, cpu);
> +
> +	/*
> +	 * Call to tick_nohz_start_idle stops the last_update_time from being
> +	 * updated. Thus, it must not be called in the event we are called from
> +	 * irq_exit() with the prior state different than idle.
> +	 */
> +	if (!inidle && !ts->inidle)
> +		return;

Calling return without restoring the
local_irq_save(flags) right above the
line where you get the CPU number seems
like a bad idea.

-- 
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