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

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Message-ID: <Z9ifV3UcLPNvBttF@slm.duckdns.org>
Date: Mon, 17 Mar 2025 12:16:55 -1000
From: Tejun Heo <tj@...nel.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: Peter Zijlstra <peterz@...radead.org>, 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

Hello,

On Mon, Mar 17, 2025 at 10:48:16PM +0100, Joel Fernandes wrote:
...
> Just to clarify, Tejun is suggesting that in mixed mode, we boost EXT
> independent of FAIR. And in normal mode, we we boost both FAIR+EXT, because well
> - nothing would be running as fair anyway.
> 
> But what is the point of doing that, if we have boost EXT independent of FAIR
> anyway? We need that code _anyway_ due to mixed mode so it would not simplify
> anything.
> 
> Or did Tejun mean something else about "toggle the reservations"?

My understanding is that if we have both FAIR and EXT's DL servers reserving
execution time all the time, we'd be reserving execution time for something
which can't be active, so the only change necessary I think is just
retracting FAIR's or EXT's reservation whent we know they are not active
(ie. if EXT is not loaded or EXT is loaded in full-sys mode).

Thanks.

-- 
tejun