linux-kernel - Re: [PATCH v6 21/21] Documentation: arm64: describe asymmetric 32-bit support

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Date:   Fri, 21 May 2021 18:37:21 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Will Deacon <will@...nel.org>
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>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...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>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, kernel-team@...roid.com
Subject: Re: [PATCH v6 21/21] Documentation: arm64: describe asymmetric
 32-bit support

On 05/18/21 10:47, Will Deacon wrote:
> Document support for running 32-bit tasks on asymmetric 32-bit systems
> and its impact on the user ABI when enabled.
> 
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  .../admin-guide/kernel-parameters.txt         |   3 +
>  Documentation/arm64/asymmetric-32bit.rst      | 149 ++++++++++++++++++
>  Documentation/arm64/index.rst                 |   1 +
>  3 files changed, 153 insertions(+)
>  create mode 100644 Documentation/arm64/asymmetric-32bit.rst
> 

[...]

> +Cpusets
> +-------
> +
> +The affinity of a 32-bit task may include CPUs that are not explicitly
> +allowed by the cpuset to which it is attached. This can occur as a
> +result of the following two situations:
> +
> +  - A 64-bit task attached to a cpuset which allows only 64-bit CPUs
> +    executes a 32-bit program.
> +
> +  - All of the 32-bit-capable CPUs allowed by a cpuset containing a
> +    32-bit task are offlined.
> +
> +In both of these cases, the new affinity is calculated according to step
> +(2) of the process described in `execve(2)`_ and the cpuset hierarchy is
> +unchanged irrespective of the cgroup version.

nit: Should we call out that we're breaking cpuset-v1 behavior? Don't feel
strongly about it.

Cheers

--
Qais Yousef