linux-kernel - Re: [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed

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Date:   Thu, 19 Nov 2020 17:09:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        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>,
        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>,
        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 07/14] sched: Introduce restrict_cpus_allowed_ptr() to
 limit task CPU affinity

On Thu, Nov 19, 2020 at 01:13:20PM +0000, Will Deacon wrote:

> Sure, but I was talking about what userspace sees, and I don't think it ever
> sees CPUs that have been hotplugged off, right? That is, sched_getaffinity()
> masks its result with the active_mask.

# for i in /sys/devices/system/cpu/cpu*/online; do echo -n $i ":"; cat $i; done
/sys/devices/system/cpu/cpu1/online :0
/sys/devices/system/cpu/cpu2/online :1
/sys/devices/system/cpu/cpu3/online :1
/sys/devices/system/cpu/cpu4/online :1
/sys/devices/system/cpu/cpu5/online :1
/sys/devices/system/cpu/cpu6/online :1
/sys/devices/system/cpu/cpu7/online :1

# grep Cpus_allowed /proc/self/status
Cpus_allowed:   ff
Cpus_allowed_list:      0-7


:-)