linux-kernel - Re: [PATCH v3] sched: async unthrottling for cfs bandwidth

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Message-ID: <Y3ymBOfRikUci/PD@hirez.programming.kicks-ass.net>
Date:   Tue, 22 Nov 2022 11:35:48 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Chengming Zhou <zhouchengming@...edance.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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>,
        Christian Brauner <brauner@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>
Subject: Re: [PATCH v3] sched: async unthrottling for cfs bandwidth

On Mon, Nov 21, 2022 at 11:37:14AM -0800, Josh Don wrote:
> Yep, this tradeoff feels "best", but there are some edge cases where
> this could potentially disrupt fairness. For example, if we have
> non-trivial W, a lot of cpus to iterate through for dispatching remote
> unthrottle, and quota is small. Doesn't help that the timer is pinned
> so that this will continually hit the same cpu.

We could -- if we wanted to -- manually rotate the timer around the
relevant CPUs. Doing that sanely would require a bit of hrtimer surgery
though I'm afraid.