linux-kernel - Re: [PATCH] sched/fair: Reschedule the cfs

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Date: Mon, 27 May 2024 10:05:03 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mike Galbraith <efault@....de>, kprateek.nayak@....com
Cc: Chunxin Zang <spring.cxz@...il.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, yu.c.chen@...el.com,
	yangchen11@...iang.com, zhouchunhua@...iang.com,
	zangchunxin@...iang.com
Subject: Re: [PATCH] sched/fair: Reschedule the cfs_rq when current is
 ineligible

On Sat, May 25, 2024 at 08:41:28AM +0200, Mike Galbraith wrote:

> -	if (pick_eevdf(cfs_rq) == pse)
> -		goto preempt;
> -
> -	return;
> +	if (pick_eevdf(cfs_rq) == se)
> +		return;

Right, this will preempt more.

This is probably going to make Prateek's case worse though. Then again,
I was already leaning to towards not making his stronger slice
protection default, because it simply hurts too much elsewhere.

Still, his observation that placing tasks can move V left which in turn
can cause the just scheduled in current non-eligible and cause
over-scheduling is valid -- just not sure what to do about it yet.