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

From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Josef Bacik <jbacik@fb.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	riel@redhat.com, mingo@redhat.com, linux-kernel@vger.kernel.org,
	morten.rasmussen@arm.com
Subject: Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE
Date: Thu, 18 Jun 2015 02:55:39 +0200	[thread overview]
Message-ID: <1434588939.3444.25.camel@gmail.com> (raw)
In-Reply-To: <5581B70D.2000800@fb.com>

On Wed, 2015-06-17 at 11:06 -0700, Josef Bacik wrote:
> On 06/11/2015 10:35 PM, Mike Galbraith wrote:
> > On Thu, 2015-05-28 at 13:05 +0200, Peter Zijlstra wrote:

> > If sd == NULL, we fall through and try to pull wakee despite nacked-by
> > tsk_cpus_allowed() or wake_affine().
> >
> 
> So maybe add a check in the if (sd_flag & SD_BALANCE_WAKE) for something 
> like this
> 
> if (tmp >= 0) {
> 	new_cpu = tmp;
> 	goto unlock;
> } else if (!want_affine) {
> 	new_cpu = prev_cpu;
> }
> 
> so we can make sure we're not being pushed onto a cpu that we aren't 
> allowed on?  Thanks,

The buglet is a messenger methinks.  You saying the patch helped without
SD_BALANCE_WAKE being set is why I looked.  The buglet would seem to say
that preferring cache is not harming your load after all.  It now sounds
as though wake_wide() may be what you're squabbling with.

Things aren't adding up all that well.

	-Mike