linux-kernel - Re: [PATCH v3 09/14] cpuset: Don't use the cpu_possible

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Message-ID: <20201119110645.GC3946@willie-the-truck>
Date:   Thu, 19 Nov 2020 11:06:45 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 09/14] cpuset: Don't use the cpu_possible_mask as a
 last resort for cgroup v1

On Thu, Nov 19, 2020 at 09:29:22AM +0000, Quentin Perret wrote:
> On Friday 13 Nov 2020 at 09:37:14 (+0000), Will Deacon wrote:
> > If the scheduler cannot find an allowed CPU for a task,
> > cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask
> > if cgroup v1 is in use.
> > 
> > In preparation for allowing architectures to provide their own fallback
> > mask, just return early if we're not using cgroup v2 and allow
> > select_fallback_rq() to figure out the mask by itself.
> > 
> > Cc: Li Zefan <lizefan@...wei.com>
> > Cc: Tejun Heo <tj@...nel.org>
> > Cc: Johannes Weiner <hannes@...xchg.org>
> > Signed-off-by: Will Deacon <will@...nel.org>
> 
> That makes select_fallback_rq() slightly more expensive if you're using
> cgroup v1, but I don't expect that be really measurable in real-world
> workloads, so:
> 
> Reviewed-by: Quentin Perret <qperret@...gle.com>

Cheers!

Will