linux-kernel - Re: [PATCH 08/15] sched: Commit to EEVDF

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Date:   Thu, 22 Jun 2023 09:11:17 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, corbet@....net,
        qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, pjt@...gle.com, pavel@....cz,
        qperret@...gle.com, tim.c.chen@...ux.intel.com, joshdon@...gle.com,
        timj@....org, kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, efault@....de, tglx@...utronix.de
Subject: Re: [PATCH 08/15] sched: Commit to EEVDF

On 6/22/23 08:01, Ingo Molnar wrote:
> 
> * Joel Fernandes <joel@...lfernandes.org> wrote:
> 
>> On Wed, May 31, 2023 at 01:58:47PM +0200, Peter Zijlstra wrote:
>>> EEVDF is a better defined scheduling policy, as a result it has less
>>> heuristics/tunables. There is no compelling reason to keep CFS around.
>>>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>> ---
>>>   kernel/sched/debug.c    |    6
>>>   kernel/sched/fair.c     |  465 +++---------------------------------------------
>>
>> Whether EEVDF helps us improve our CFS latency issues or not, I do like the
>> merits of this diffstat alone and the lesser complexity and getting rid of
>> those horrible knobs is kinda nice.
> 
> To to be fair, the "removal" in this patch is in significant part an
> artifact of the patch series itself, because first EEVDF bits get added by
> three earlier patches, in parallel to CFS:
> 
>   kernel/sched/fair.c     |  137 +++++++++++++++++++++++++++++++++++++++++++++++++--
>   kernel/sched/fair.c     |  162 +++++++++++++++++++++++++++++++++++++-----------
>   kernel/sched/fair.c     |  338 +++++++++++++++++++++++++++++++++++++++++-------
> 
> ... and then we remove the old CFS policy code in this 'commit to EEVDF' patch:
> 
>   kernel/sched/fair.c     |  465 +++---------------------------------------------
> 
> The combined diffstat is close to 50% / 50% balanced:
> 
>   kernel/sched/fair.c              | 1105 ++++++++++++++++++--------------------
> 
> But having said that, I do agree that EEVDF as submitted by Peter is better
> defined, with fewer heuristics, which is an overall win - so no complaints
> from me!

Agreed, thank you for correcting me on the statistics.

  - Joel