Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE

[Josef Bacik]

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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