linux-kernel - Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE

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Message-ID: <556CD993.3060909@redhat.com>
Date:	Mon, 01 Jun 2015 18:15:47 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Josef Bacik <jbacik@...com>, Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	umgwanakikbuti@...il.com, morten.rasmussen@....com,
	kernel-team <Kernel-team@...com>
Subject: Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for
 BALANCE_WAKE

On 06/01/2015 03:38 PM, Josef Bacik wrote:

> Ok I got this patch to give me the same performance as all our other
> crap, just need to apply this incremental
> 
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b71eb2b..e11cfec 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4761,13 +4761,10 @@ select_task_rq_fair(struct task_struct *p, int
> prev_cpu, int sd_flag, int wake_f
> 
>          if (tmp->flags & sd_flag)
>              sd = tmp;
> -        else if (!want_affine || (want_affine && affine_sd))
> -            break;
>      }
> 
>      if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync)) {
>          prev_cpu = cpu;
> -        sd = NULL; /* WAKE_AFFINE trumps BALANCE_WAKE */

Given Peter's worries about wake_affine and affine_sd,
should the above be sd = affine_sd, in case select_idle_sibling
cannot find an idle sibling?

That way we can attempt to at least find an idle cpu inside
the affine_sd.

Of course, there may be subtleties here I am overlooking...

>      }
> 
>      if (sd_flag & SD_BALANCE_WAKE) {


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