linux-kernel - Re: [RESEND PATCH] sched/fair: consider RT/IRQ pressure in select_idle

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Date:   Fri, 9 Feb 2018 13:37:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Rohit Jain <rohit.k.jain@...cle.com>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, steven.sistare@...cle.com,
        dhaval.giani@...cle.com,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        "Cc: EAS Dev" <eas-dev@...ts.linaro.org>
Subject: Re: [RESEND PATCH] sched/fair: consider RT/IRQ pressure in
 select_idle_sibling

On Mon, Feb 05, 2018 at 10:50:41PM -0800, Joel Fernandes wrote:

> That's Ok with me. Just that I remember Peter messing with this path
> and that it was expensive to scan too much for some systems. The other
> thing is you're really doing to do a "fail safe" as you call it search
> here with SIS_PROP set. Do you see a difference in perf when doing the
> same approach as you took in select_idle_core?
> 
> Peter, are you with the approach Rohit has adopted to pick best
> capacity idle CPU in select_idle_cpu? I guess nr--; will bail out
> early if we have SIS_PROP set, incase the scan cost gets too much but
> then again we might end scanning too few CPUs.

_IF_ you want to consider capacity, I don't think there's much else you
can do. And yes, nr-- might have to save the day more often.