linux-kernel - Re: [RFC][PATCH] sched/ext: Split curr|donor references properly

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Message-ID: <aTRSzTVeGfME1N5y@slm.duckdns.org>
Date: Sat, 6 Dec 2025 05:59:09 -1000
From: Tejun Heo <tj@...nel.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: John Stultz <jstultz@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
	Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Valentin Schneider <vschneid@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Zimuzo Ezeozue <zezeozue@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Metin Kaya <Metin.Kaya@....com>,
	Xuewen Yan <xuewen.yan94@...il.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>,
	Changwoo Min <changwoo@...lia.com>, sched-ext@...ts.linux.dev,
	kernel-team@...roid.com
Subject: Re: [RFC][PATCH] sched/ext: Split curr|donor references properly

Hello,

On Sat, Dec 06, 2025 at 09:56:50AM -0500, Joel Fernandes wrote:
...
> At a high level, my understanding is BPF schedulers have a lot of say in how to
> schedule including precise time slice and preemption control (give or take level
> of control and performance reasons). You can in fact have your own 'userland'
> queues that the kernel is unaware, IIUC. I am not sure if proxy exec will
> transparently work for all those usecases. It will probably work properly only
> when BPF scheduling in userland is simple and most of the scheduling is done by
> non-BPF kernel code.

Maybe this can be resolved by proxy execution explicitly telling sched_ext
to essentially dequeue the proxy-executed task so that it's kept more
transparent. However, I wonder whether it'd be a useful first step to first
deconflict the two config options. ie. Allow sched_ext loading disable proxy
execution dynamically so that people don't have to choose between the two
config options. I don't know the code intimately, but, from just skimming
it, it looks like it can be drained with a static key and some percpu
counters.

Thanks.

-- 
tejun