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From:   Barry Song <21cnbao@gmail.com>
To:     longman@redhat.com
Cc:     amit.pundir@linaro.org, cgroups@vger.kernel.org,
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Subject: Re: [PATCH RFC] cpuset: Make cpusets get restored on hotplug
Date:   Wed, 27 Oct 2021 12:58:08 +1300
Message-Id: <20211026235808.34168-1-21cnbao@gmail.com>
In-Reply-To: <972a5c1b-6721-ac20-cec5-617af67e617d@redhat.com>
References: <972a5c1b-6721-ac20-cec5-617af67e617d@redhat.com>
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> I think Tejun is concerned about a change in the default behavior of
> cpuset v1.
>
> There is a special v2 mode for cpuset that is enabled by the mount
> option "cpuset_v2_mode". This causes the cpuset v1 to adopt some of the
> v2 behavior. I introduced this v2 mode a while back to address, I think,
> a similar concern. Could you try that to see if it is able to address
> your problem? If not, you can make some code adjustment within the
> framework of the v2 mode. As long as it is an opt-in, I think we are
> open to further change.

I am also able to reproduce on Ubuntu 21.04 LTS.

all docker will be put in this cgroups and its child cgroups:
/sys/fs/cgroup/cpuset/docker

disabling and enabling SMT by:
echo off > /sys/devices/system/cpu/smt/control
echo on > /sys/devices/system/cpu/smt/control

or unpluging and pluging CPUs by:
echo 0 > /sys/devices/system/cpu/cpuX/online
echo 1 > /sys/devices/system/cpu/cpuX/online

then all docker images will lose some CPUs.

So should we document the broken behaviours somewhere?

Thanks
barry