linux-kernel - Re: [PATCH 13/14] sched: Add {DE,EN}QUEUE

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Message-ID: <aMXw-xvmGIZ9-UFJ@slm.duckdns.org>
Date: Sat, 13 Sep 2025 12:32:27 -1000
From: Tejun Heo <tj@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, longman@...hat.com, hannes@...xchg.org,
	mkoutny@...e.com, void@...ifault.com, arighi@...dia.com,
	changwoo@...lia.com, cgroups@...r.kernel.org,
	sched-ext@...ts.linux.dev, liuwenfang@...or.com, tglx@...utronix.de
Subject: Re: [PATCH 13/14] sched: Add {DE,EN}QUEUE_LOCKED

Hello,

On Fri, Sep 12, 2025 at 06:32:32AM -1000, Tejun Heo wrote:
> Yeah, or I can make scx_tasks iteration smarter so that it can skip through
> the list for tasks which aren't runnable. As long as it doesn't do lock ops
> on every task, it should be fine. I think this is solvable one way or
> another. Let's continue in the other subthread.

Thought more about it. There's another use case for this runnable list,
which is the watchdog. As in the migration synchronization, I think the
right thing to do here is just adding a nested lock. That doesn't add any
overhead or complications to other sched classes and from sched_ext POV
given how expensive migrations can be, if we make that a bit cheaper (and I
believe we will with changes being discussed), added up, the outcome would
likely be lower overhead.

Thanks.

-- 
tejun