linux-kernel - Re: [PATCH 2/2] sched/fair: Reimplement NEXT

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Message-ID: <20251028150951.GD4067720@noisy.programming.kicks-ass.net>
Date: Tue, 28 Oct 2025 16:09:51 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Mel Gorman <mgorman@...hsingularity.net>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Valentin Schneider <vschneid@...hat.com>,
	Chris Mason <clm@...a.com>
Subject: Re: [PATCH 2/2] sched/fair: Reimplement NEXT_BUDDY to align with
 EEVDF goals

On Mon, Oct 27, 2025 at 01:39:15PM +0000, Mel Gorman wrote:
> +enum preempt_wakeup_action {
> +	PREEMPT_WAKEUP_NONE,		/* No action on the buddy */
> +	PREEMPT_WAKEUP_NEXT,		/* Check next is most eligible
> +					 * before rescheduling.
> +					 */
> +	PREEMPT_WAKEUP_RESCHED,		/* Plain reschedule */
> +};

In pre-existing code that isn't modified by this patch, we have:

  if (do_preempt_short)

Which seems to hard rely on PREEMPT_WAKEUP_NONE being 0, please make
that explicit in the enum above.