linux-kernel - Re: [PATCH v8 07/19] cpuset: Honour task_cpu_possible_mask() in guarantee_online

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Message-ID: <875yyteerr.mognet@arm.com>
Date:   Fri, 04 Jun 2021 18:11:20 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Will Deacon <will@...nel.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>,
        Quentin Perret <qperret@...gle.com>, Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        kernel-team@...roid.com, Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH v8 07/19] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()

On 02/06/21 17:47, Will Deacon wrote:
> Asymmetric systems may not offer the same level of userspace ISA support
> across all CPUs, meaning that some applications cannot be executed by
> some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
> not feature support for 32-bit applications on both clusters.
>
> Modify guarantee_online_cpus() to take task_cpu_possible_mask() into
> account when trying to find a suitable set of online CPUs for a given
> task. This will avoid passing an invalid mask to set_cpus_allowed_ptr()
> during ->attach() and will subsequently allow the cpuset hierarchy to be
> taken into account when forcefully overriding the affinity mask for a
> task which requires migration to a compatible CPU.
>
> 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>

Reviewed-by: Valentin Schneider <Valentin.Schneider@....com>