linux-kernel - Re: [PATCH V3 5/7] mmc: queue work on any cpu

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Date:	Tue, 19 Mar 2013 08:58:52 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	pjt@...gle.com, paul.mckenney@...aro.org, tglx@...utronix.de,
	tj@...nel.org, suresh.b.siddha@...el.com, venki@...gle.com,
	mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org,
	linaro-kernel@...ts.linaro.org, robin.randhawa@....com,
	Steve.Bannister@....com, Liviu.Dudau@....com,
	charles.garcia-tobin@....com, Arvind.Chauhan@....com,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chris Ball <cjb@...top.org>, linux-mmc@...r.kernel.org
Subject: Re: [PATCH V3 5/7] mmc: queue work on any cpu

On 18 March 2013 16:23, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> mmc uses workqueues for running mmc_rescan(). There is no real dependency of
> scheduling these on the cpu which scheduled them.
>
> On a idle system, it is observed that and idle cpu wakes up many times just to
> service this work. It would be better if we can schedule it on a cpu which isn't
> idle to save on power.
>
> By idle cpu (from scheduler's perspective) we mean:
> - Current task is idle task
> - nr_running == 0
> - wake_list is empty
>
> This patch replaces the queue_delayed_work() with
> queue_delayed_work_on_any_cpu() siblings.
>
> This routine would look for the closest (via scheduling domains) non-idle cpu
> (non-idle from schedulers perspective). If the current cpu is not idle or all
> cpus are idle, work will be scheduled on local cpu.
>
> Cc: Chris Ball <cjb@...top.org>
> Cc: linux-mmc@...r.kernel.org
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/mmc/core/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 9290bb5..adf331a 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -85,7 +85,7 @@ MODULE_PARM_DESC(
>  static int mmc_schedule_delayed_work(struct delayed_work *work,
>                                      unsigned long delay)
>  {
> -       return queue_delayed_work(workqueue, work, delay);
> +       return queue_delayed_work_on_any_cpu(workqueue, work, delay);
>  }
>
>  /*
> --
> 1.7.12.rc2.18.g61b472e
>
> --
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Acked-by: Ulf Hansson <ulf.hansson@...aro.org>
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