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Subject: Re: [PATCH v13 01/11] cpuset: Enable cpuset controller in default
 hierarchy
To:     Waiman Long <longman@redhat.com>, Tejun Heo <tj@kernel.org>,
        Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>
Cc:     cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, kernel-team@fb.com, pjt@google.com,
        luto@amacapital.net, Mike Galbraith <efault@gmx.de>,
        torvalds@linux-foundation.org, Roman Gushchin <guro@fb.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>
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From:   Tom Hromatka <tom.hromatka@oracle.com>
Message-ID: <f461a6b4-fe95-ab7c-675a-734a02342a6d@oracle.com>
Date:   Mon, 15 Oct 2018 13:10:52 -0600
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On 10/15/2018 12:41 PM, Waiman Long wrote:
> On 10/15/2018 02:31 PM, Tom Hromatka wrote:
>>
>> On 10/12/2018 11:55 AM, Waiman Long wrote:
>>> Given the fact that thread mode had been merged into 4.14, it is now
>>> time to enable cpuset to be used in the default hierarchy (cgroup v2)
>>> as it is clearly threaded.
>>>
>>> The cpuset controller had experienced feature creep since its
>>> introduction more than a decade ago. Besides the core cpus and mems
>>> control files to limit cpus and memory nodes, there are a bunch of
>>> additional features that can be controlled from the userspace. Some of
>>> the features are of doubtful usefulness and may not be actively used.
>>>
>>> This patch enables cpuset controller in the default hierarchy with
>>> a minimal set of features, namely just the cpus and mems and their
>>> effective_* counterparts.  We can certainly add more features to the
>>> default hierarchy in the future if there is a real user need for them
>>> later on.
>> I really appreciate this simplification of the cpuset controller.
>>
>> I currently have an in-house customer that is unhappy with the
>> way cgroups cpuset v1 handles offlined CPUs.  This patchset makes two
>> significant improvements over current cpuset v1 behavior.  1) It allows
>> for offlined CPUs to be added to a cpuset (even though the CPU is
>> offline) and 2) it restores CPUs back to the requested cpuset when they
>> come back online.  This is more intuitive and secure for my customers.
>> Thank you!
>>
>> In part because of this patchset, I plan on proposing similar behavior
>> for offlined CPUs to cpuset v1.
>>
>> Thanks.
>>
>> Tom
> If you are just talking about the ability for cpuset to revert back to
> its original state when an offlined CPU becomes online again, that
> capability can be activated in v1 using the "cpuset_v2_mode" mount
> option when mounting the cpuset cgroup. However, that is not the default
> for v1.
>
> -Longman
>
>

Thanks!!!  I didn't realize cpuset_v2_mode exists.  (I see you
added it last year.  Thank you!)  I'll try it out and see if it
meets my customer's needs.

Tom