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Fri, 13 Jun 2025 12:20:59 +0200 Message-ID: Subject: Re: [RFC][PATCH 2/5] sched: Optimize ttwu() / select_task_rq() From: Mike Galbraith To: Peter Zijlstra Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, clm@meta.com, linux-kernel@vger.kernel.org Date: Fri, 13 Jun 2025 12:20:56 +0200 In-Reply-To: <20250613094052.GF2278213@noisy.programming.kicks-ass.net> References: <20250520094538.086709102@infradead.org> <20250520101727.620602459@infradead.org> <334e48ebbf34d853777672449cb29d5f06c751b7.camel@gmx.de> <20250613094052.GF2278213@noisy.programming.kicks-ass.net> Autocrypt: addr=efault@gmx.de; keydata=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 y6yrWaxyqUg8CnZF/J5HR+IvRK+vu85xxwSLQsrVONH0Ita1jg2nhUW7yLZer8xrhxIuYCqrMgreo5BAA3+irHy37rmqiAFZcnDnCNDtJ4sz48tiEkEGBECAAkFAk/h0fkCGwwACgkQxiYAKcZ9tvgIMQCeIcgjSxwbGiGn2q/cv8IvHf1r/DIAnivw+bGITqTU7rhgfwe07dhBoIdz Content-Type: text/plain; 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so the problem being that we can race with > migrate_disable_switch(). Yeah. Most of the time when we do fallback saves us, but we can and do zip past it, and that turns box various shades of sad. >=20 > Does something like this help? It surely will, but I'll testdrive it. No news is good news. > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3593,7 +3593,7 @@ int select_task_rq(struct task_struct *p > =C2=A0 cpu =3D p->sched_class->select_task_rq(p, cpu, > *wake_flags); > =C2=A0 *wake_flags |=3D WF_RQ_SELECTED; > =C2=A0 } else { > - cpu =3D cpumask_any(p->cpus_ptr); > + cpu =3D task_cpu(p); > =C2=A0 } > =C2=A0 > =C2=A0 /*