linux-kernel - Re: [PATCH 0/8] sched/fair: misfit task load-balance tweaks

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Date:   Wed, 3 Feb 2021 15:14:00 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Quentin Perret <qperret@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 0/8] sched/fair: misfit task load-balance tweaks

On 01/28/21 18:31, Valentin Schneider wrote:
> Hi folks,
> 
> Here is this year's series of misfit changes. On the menu:
> 
> o Patch 1 is an independent active balance cleanup
> o Patch 2 adds some more sched_asym_cpucapacity static branches
> o Patch 3 introduces yet another margin for capacity to capacity
>   comparisons
> o Patches 4-6 build on top of patch 3 and change capacity comparisons
>   throughout misfit load balancing  
> o Patches 7-8 fix some extra misfit issues I've been seeing on "real"
>   workloads.
> 
> IMO the somewhat controversial bit is patch 3, because it attempts to solve
> margin issues by... Adding another margin. This does solve issues on
> existing platforms (e.g. Pixel4), but we'll be back to square one the day
> some "clever" folks spin a platform with two different CPU capacities less than
> 5% apart.

One more margin is a cause of apprehension to me. But in this case I think it
is the appropriate thing to do now. I can't think of a scenario where this
could hurt.

Thanks

--
Qais Yousef