linux-kernel - Re: [PATCH 3/3] workqueue: Schedule work on non-idle cpu instead of current one

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Date:	Tue, 25 Sep 2012 13:22:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linux-kernel@...r.kernel.org, pjt@...gle.com,
	paul.mckenney@...aro.org, tglx@...utronix.de, tj@...nel.org,
	suresh.b.siddha@...el.com, venki@...gle.com, mingo@...hat.com,
	robin.randhawa@....com, Steve.Bannister@....com,
	Arvind.Chauhan@....com, amit.kucheria@...aro.org,
	vincent.guittot@...aro.org, linaro-dev@...ts.linaro.org,
	patches@...aro.org
Subject: Re: [PATCH 3/3] workqueue: Schedule work on non-idle cpu instead of
 current one

On Tue, 2012-09-25 at 16:06 +0530, Viresh Kumar wrote:
> @@ -1066,8 +1076,9 @@ int queue_work(struct workqueue_struct *wq,
> struct work_struct *work)
>  {
>         int ret;
>  
> -       ret = queue_work_on(get_cpu(), wq, work);
> -       put_cpu();
> +       preempt_disable();
> +       ret = queue_work_on(wq_select_cpu(), wq, work);
> +       preempt_enable();
>  
>         return ret;
>  }

Right, so the problem I see here is that wq_select_cpu() is horridly
expensive..

> @@ -1102,7 +1113,7 @@ static void delayed_work_timer_fn(unsigned long
> __data)
>         struct delayed_work *dwork = (struct delayed_work *)__data;
>         struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);
>  
> -       __queue_work(smp_processor_id(), cwq->wq, &dwork->work);
> +       __queue_work(wq_select_cpu(), cwq->wq, &dwork->work);
>  } 

Shouldn't timer migration have sorted this one?
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