linux-kernel - Re: [RFC PATCH] sched: wake-affine throttle

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Message-ID: <1365415249.2609.145.camel@laptop>
Date:	Mon, 08 Apr 2013 12:00:49 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...nel.org>,
	Alex Shi <alex.shi@...el.com>, Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Ram Pai <linuxram@...ibm.com>
Subject: Re: [RFC PATCH] sched: wake-affine throttle

On Mon, 2013-03-25 at 13:24 +0800, Michael Wang wrote:
>         if (affine_sd) {
> -               if (cpu != prev_cpu && wake_affine(affine_sd, p,
> sync))
> +               if (cpu != prev_cpu && wake_affine(affine_sd, p,
> sync)) {
> +                       /*
> +                        * wake_affine() stuff try to pull wakee to
> the cpu
> +                        * around waker, this will benefit us if the
> data
> +                        * cached on waker cpu is hot for wakee, or
> the extreme
> +                        * ping-pong case.
> +                        *
> +                        * However, do such blindly work too
> frequently will
> +                        * cause regression to some workload, thus,
> each time
> +                        * when wake_affine() succeed, throttle it for
> a while.
> +                        */
> +                       wake_affine_throttle(p);
>                         prev_cpu = cpu;
> +               }

How about only throttling when wake_affine() starts returning false? At
that point its lost its benefit.

Also, why not place this inside wake_affine() like you did the throttled
test.

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