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

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Message-ID: <jhjim792dro.mognet@arm.com>
Date:   Wed, 03 Feb 2021 18:43:23 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Qais Yousef <qais.yousef@....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

Hi Qais,

On 03/02/21 15:14, Qais Yousef wrote:
> 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 for having a look!

> Thanks
>
> --
> Qais Yousef