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

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Date:	Mon, 1 Jun 2015 15:38:16 -0400
From:	Josef Bacik <jbacik@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	<riel@...hat.com>, <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 05/29/2015 05:03 PM, Josef Bacik wrote:
> On 05/28/2015 07:05 AM, Peter Zijlstra wrote:
>>
>> So maybe you want something like the below; that cures the thing Morten
>> raised, and we continue looking for sd, even after we found affine_sd.
>>
>> It also avoids the pointless idle_cpu() check Mike raised by making
>> select_idle_sibling() return -1 if it doesn't find anything.
>>
>> Then it continues doing the full balance IFF sd was set, which is keyed
>> off of sd->flags.
>>
>> And note (as Mike already said), BALANCE_WAKE does _NOT_ look for idle
>> CPUs, it looks for the least loaded CPU. And its damn expensive.
>>
>>
>> Rewriting this entire thing is somewhere on the todo list :/
>>
>

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 */
  	}

  	if (sd_flag & SD_BALANCE_WAKE) {

And everything works fine.  Does that seem reasonable?  Thanks,

Josef
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