linux-kernel - Re: [PATCH RFC 3/8] sched/ext: Add a DL server for sched

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Message-ID: <20250317170602.GE6888@noisy.programming.kicks-ass.net>
Date: Mon, 17 Mar 2025 18:06:02 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Tejun Heo <tj@...nel.org>
Cc: Joel Fernandes <joelagnelf@...dia.com>, linux-kernel@...r.kernel.org,
	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>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>,
	Luigi De Matteis <ldematteis123@...il.com>, paulmck@...nel.org,
	boqun.feng@...il.com
Subject: Re: [PATCH RFC 3/8] sched/ext: Add a DL server for sched_ext tasks

On Mon, Mar 17, 2025 at 06:57:19AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Mon, Mar 17, 2025 at 11:31:01AM +0100, Peter Zijlstra wrote:
> > On Sat, Mar 15, 2025 at 07:15:27PM -0400, Joel Fernandes wrote:
> > > If so, that will not handle the case where the system has both
> > > FAIR and EXT tasks in the mix (EXT has a partial mode where certain tasks can be
> > > made EXT with certain others left as FAIR) and FAIR runs 100% and starves EXT.
> > 
> > Well, you did not mention that issue, you only babbled about RT.
> > 
> > I did point out that issue with ext, and TJ said this mixed mode wasn't
> > really meant to be used or somesuch.
> 
> It's true that most of the current use cases don't use mixed mode. That
> said, some folks are interested in it and if we can prevent starvation from
> fair saturating CPUs in mixed mode with a DL server, that'd be really nice.
> Would it be possible to toggle the reservations depending on the ext's
> operation mode?

Yeah, that should be doable.