linux-kernel - Re: [PATCH RFC] sched_ext: Choose prev_cpu if idle and cache affine without WF

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Message-ID: <Z9i6-_R_LLqt8mq4@slm.duckdns.org>
Date: Mon, 17 Mar 2025 14:14:51 -1000
From: Tejun Heo <tj@...nel.org>
To: Libo Chen <libo.chen@...cle.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>, linux-kernel@...r.kernel.org,
	David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCH RFC] sched_ext: Choose prev_cpu if idle and cache affine
 without WF_SYNC

On Mon, Mar 17, 2025 at 05:12:25PM -0700, Libo Chen wrote:
> Just as Peter said, this is whole wake affinity thing is highly workload
> dependent. We have seen cases where even if there are idle cores in the
> prev node, it's still beneficial to cross the NUMA boundary. Will it make
> more sense to have the BPF scheduler implement/alter some of logic here so
> it can fit to different workload?

Oh yeah, multiple SCX schedulers already implement their own select_cpu().
This discussion is just around the default implementation which can be used
if a BPF scheduler doesn't want to implement its own.

Thanks.

-- 
tejun