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

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Message-ID: <20251112144823.GE3245006@noisy.programming.kicks-ass.net>
Date: Wed, 12 Nov 2025 15:48:23 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Mel Gorman <mgorman@...hsingularity.net>
Cc: 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>,
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] sched/fair: Reimplement NEXT_BUDDY to align with
 EEVDF goals

On Wed, Nov 12, 2025 at 12:25:21PM +0000, Mel Gorman wrote:

> +	/* Prefer picking wakee soon if appropriate. */
> +	if (sched_feat(NEXT_BUDDY) &&
> +	    set_preempt_buddy(cfs_rq, wake_flags, pse, se)) {
> +
> +		/*
> +		 * Decide whether to obey WF_SYNC hint for a new buddy. Old
> +		 * buddies are ignored as they may not be relevant to the
> +		 * waker and less likely to be cache hot.
> +		 */
> +		if (wake_flags & WF_SYNC)
> +			preempt_action = preempt_sync(rq, wake_flags, pse, se);
> +	}

Why only do preempt_sync() when NEXT_BUDDY? Nothing there seems to
depend on buddies.