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Message-ID: <Y9eweBuHFeO1jZCH@hirez.programming.kicks-ass.net> Date: Mon, 30 Jan 2023 12:56:40 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Waiman Long <longman@...hat.com> Cc: 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>, Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>, Will Deacon <will@...nel.org>, Phil Auld <pauld@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v3] sched: Store restrict_cpus_allowed_ptr() call state On Thu, Jan 26, 2023 at 08:55:27PM -0500, Waiman Long wrote: > The user_cpus_ptr field was originally added by commit b90ca8badbd1 > ("sched: Introduce task_struct::user_cpus_ptr to track requested > affinity"). It was used only by arm64 arch due to possible asymmetric > CPU setup. > > Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested > cpumask"), task_struct::user_cpus_ptr is repurposed to store user > requested cpu affinity specified in the sched_setaffinity(). > > This results in a slight performance regression on an arm64 > system when booted with "allow_mismatched_32bit_el0" Dude, how can you still call this a slight performance regression after Will told you time and time again that's not the problem. It clearly is a behavioural problem.
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