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

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Message-ID: <26D75017-9432-4D8F-994C-ABF0B2A9F30B@nvidia.com>
Date: Sat, 6 Dec 2025 19:30:25 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: Tejun Heo <tj@...nel.org>
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" <sched-ext@...ts.linux.dev>,
	"kernel-team@...roid.com" <kernel-team@...roid.com>
Subject: Re: [RFC][PATCH] sched/ext: Split curr|donor references properly



> On Dec 6, 2025, at 10:59 AM, Tejun Heo <tj@...nel.org> wrote:
> 
> 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.

Yes, perhaps.

> 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.

Agreed. There is also stop_machine if all else fails :)

thanks,

 - Joel

> 
> Thanks.
> 
> --
> tejun