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

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Message-ID: <ZJQ4A2Jm4VoGMKbl@gmail.com>
Date:   Thu, 22 Jun 2023 14:01:07 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.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


* 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!

Thanks,

	Ingo