linux-kernel - Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue

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Date: Mon, 29 Apr 2024 14:14:22 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mike Galbraith <efault@....de>
Cc: K Prateek Nayak <kprateek.nayak@....com>, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
	linux-kernel@...r.kernel.org, wuyun.abel@...edance.com,
	tglx@...utronix.de, Chen Yu <yu.c.chen@...el.com>,
	Oliver Sang <oliver.sang@...el.com>
Subject: Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue

On Sun, Apr 28, 2024 at 06:32:49PM +0200, Mike Galbraith wrote:
> On Sat, 2024-04-27 at 08:42 +0200, Mike Galbraith wrote:
> > On Fri, 2024-04-26 at 18:03 +0200, Mike Galbraith wrote:
> > > fwiw, tbench liked the previous version better.
> >
> > The culprit lies somewhere in the new PREEMPT_SHORT patch.
> 
> <squint>
> 
> Ah, moving the curr eligibility check into pick_curr() left an
> ineligible curr to be seen/used further down in pick_eevdf().
> 
> found:
>         if (!best || (curr && entity_before(curr, best)))
>                 best = curr;

Hmm yes, over aggressive cleanup that. Let me try again.

> Nit: PREEMPT_SHORT depending on RUN_TO_PARITY looks odd.

The thinking was that without RUN_TO_PARITY we'll always do a full pick
and it will always pick a (new) shorter deadline task over current.

The PREEMPRT_SHORT thing really is an exception to avoid RUN_TO_PARITY
from ruining latency game for short tasks.