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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250317174431.GI6888@noisy.programming.kicks-ass.net>
Date: Mon, 17 Mar 2025 18:44:31 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, Joel Fernandes <joelagnelf@...dia.com>,
	linux-kernel@...r.kernel.org, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	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 06:30:57PM +0100, Andrea Righi wrote:

> I guess the question is: what is more expensive in general on task wakeup?
> 1) a cross-node migration or 2) running on a partially busy SMT core?

That totally depends on both the workload and the actual machine :/

If you have 'fast' numa and not a very big footprint, the numa
migrations aren't too bad. OTOH if you have sucky numa or your memory
footprint is significant, then running on the wrong node is super
painful.