linux-kernel - Re: [PATCH v5 2/2] cpuset: Add cpuset.flags control knob to v2

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Date:   Tue, 20 Mar 2018 16:12:25 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        efault@....de, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>
Subject: Re: [PATCH v5 2/2] cpuset: Add cpuset.flags control knob to v2

On 03/19/2018 12:33 PM, Waiman Long wrote:
> On 03/19/2018 12:26 PM, Tejun Heo wrote:
>> Hello, Waiman.
>>
>> On Thu, Mar 15, 2018 at 05:20:42PM -0400, Waiman Long wrote:
>>> +	The currently supported flag is:
>>> +
>>> +	  sched_load_balance
>>> +		When it is not set, there will be no load balancing
>>> +		among CPUs on this cpuset.  Tasks will stay in the
>>> +		CPUs they are running on and will not be moved to
>>> +		other CPUs.
>>> +
>>> +		When it is set, tasks within this cpuset will be
>>> +		load-balanced by the kernel scheduler.  Tasks will be
>>> +		moved from CPUs with high load to other CPUs within
>>> +		the same cpuset with less load periodically.
>> Hmm... looks like this is something which can be decided by the cgroup
>> itself and should be made delegatable.  Given that different flags
>> might need different delegation settings and the precedence of
>> memory.oom_group, I think it'd be better to make the flags separate
>> bool files - ie. cpuset.sched_load_balance which contains 0/1 and
>> marked delegatable.
>>
>> Thanks.
>>
> Sure. Will do that.

After some thought, I am planning to impose the following additional
constraints on how sched_load_balance works in v2.

1) sched_load_balance will be made hierarchical, the child will inherit
the flag from its parent.
2) cpu_exclusive will be implicitly associated with sched_load_balance.
IOW, sched_load_balance => !cpu_exclusive, and !sched_load_balance =>
cpu_exclusive.
3) sched_load_balance cannot be 1 on a child if it is 0 on the parent.

With these changes, sched_load_balance will have to be set by the parent
and so will not be delegatable. Please let me know your thought on that.

Cheers,
Longman