linux-kernel - Re: [v2 patch v3.18+ regression fix] sched: Further improve spurious CPU

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Date:   Tue, 06 Sep 2016 15:59:51 +0200
From:   Mike Galbraith <umgwanakikbuti@...il.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [v2 patch v3.18+ regression fix] sched: Further improve
 spurious CPU_IDLE active migrations

On Tue, 2016-09-06 at 15:42 +0200, Vincent Guittot wrote:
> On 6 September 2016 at 15:07, Mike Galbraith <umgwanakikbuti@...il.com> wrote:
> > On Tue, 2016-09-06 at 15:01 +0200, Vincent Guittot wrote:
> > > Le Monday 05 Sep 2016 à 18:26:53 (+0200), Mike Galbraith a écrit :
> > > > Coming back to this, how about this instead, only increase the group
> > > > imbalance threshold when sd_llc_size == 2.  Newer L3 equipped
> > > > processors then aren't affected.
> > > > 
> > > 
> > > Not sure that all systems with sd_llc_size == 2 wants this behavior.
> > > 
> > > Why not adding a sched_feature for changing the 2nd half of the test
> > > for some systems ?
> > 
> > Because users won't know, and shouldn't need to know that they need to
> > flip that switch.
> 
> fair enough
> 
> so how can we detect this specific system configuration ?
> 
> sd_llc_size == 2 is not enough IMHO

Seems to me that _is_ the pertinent configuration.  If that isn't
enough, I guess we just say too bad about old multiple LLC CPUs.

	-Mike