linux-kernel - Re: [RFC][PATCH 1/3] sched: Detect per-class runqueue changes

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Message-ID: <aOTmg90J1Tdggm5z@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 7 Oct 2025 12:08:03 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: tj@...nel.org, linux-kernel@...r.kernel.org, mingo@...nel.org,
	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: [RFC][PATCH 1/3] sched: Detect per-class runqueue changes

Hi Peter,

On 06/10/25 12:46, Peter Zijlstra wrote:
> Have enqueue/dequeue set a per-class bit in rq->queue_mask. This then
> enables easy tracking of which runqueues are modified over a
> lock-break.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---

Nice.

> @@ -12887,8 +12888,8 @@ static int sched_balance_newidle(struct
>  	if (this_rq->cfs.h_nr_queued && !pulled_task)
>  		pulled_task = 1;
>  
> -	/* Is there a task of a high priority class? */
> -	if (this_rq->nr_running != this_rq->cfs.h_nr_queued)
> +	/* If a higher prio class was modified, restart the pick */
> +	if (this_rq->queue_mask & ~((fair_sched_class.queue_mask << 1)-1))
>  		pulled_task = -1;

Does this however want a self-documenting inline helper or macro to make
it even more clear? If this is always going to be the only caller maybe
not so much.

Thanks,
Juri