linux-kernel - Re: [PATCH 07/16] sched_ext: Add a DL server for sched

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Message-ID: <aLin8VayVsYyKXze@slm.duckdns.org>
Date: Wed, 3 Sep 2025 10:41:21 -1000
From: Tejun Heo <tj@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andrea Righi <arighi@...dia.com>, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Shuah Khan <shuah@...nel.org>,
	sched-ext@...ts.linux.dev, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Luigi De Matteis <ldematteis123@...il.com>
Subject: Re: [PATCH 07/16] sched_ext: Add a DL server for sched_ext tasks

Hello,

On Wed, Sep 03, 2025 at 10:08:22PM +0200, Peter Zijlstra wrote:
> > I'm a bit confused. This series doesn't have prep patches to add @rf to
> > dl_server_pick_f. Is this the right patch?
> 
> Patch 14 seems to be the proposed alternative, and I'm not liking that
> at all.
> 
> That rf passing was very much also needed for that other issue; I'm not
> sure why that's gone away.

Using balance() was my suggestion to stay within the current framework. If
we want to add @rf to pick_task(), that's more fundamental change. We
dropped the discussion in the other thread but I found it odd to add @rf to
pick_task() while disallowing the use of @rf in non-dl-server pick path and
if we want to allow that, we gotta solve the race between pick_task()
dropping rq lock and the ttwu inserting high pri task.

Thanks.

-- 
tejun