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

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Message-ID: <CAKfTPtD6gJVRyqE_GiKtE+T1osG-J_TnbHu7jYRy0qJjQCCQMw@mail.gmail.com>
Date:   Tue, 6 Sep 2016 15:42:24 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Mike Galbraith <umgwanakikbuti@...il.com>
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 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

>
>         -Mike