linux-kernel - Re: [RFC PATCH 2/3] sched/cpuset: Keep track of SCHED

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Date:   Wed, 22 Mar 2023 15:05:25 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Waiman Long <longman@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org,
        cgroups@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [RFC PATCH 2/3] sched/cpuset: Keep track of SCHED_DEADLINE tasks
 in cpusets

On 15/03/2023 19:01, Waiman Long wrote:
> 
> On 3/15/23 13:14, Juri Lelli wrote:
>> On 15/03/23 11:46, Waiman Long wrote:
>>> On 3/15/23 08:18, Juri Lelli wrote:

[...]

>>>> @@ -2472,6 +2492,11 @@ static int cpuset_can_attach(struct
>>>> cgroup_taskset *tset)
>>>>            ret = security_task_setscheduler(task);
>>>>            if (ret)
>>>>                goto out_unlock;
>>>> +
>>>> +        if (dl_task(task)) {
>>>> +            cs->nr_deadline_tasks++;
>>>> +            cpuset_attach_old_cs->nr_deadline_tasks--;
>>>> +        }
>>>>        }
>>> Any one of the tasks in the cpuset can cause the test to fail and
>>> abort the
>>> attachment. I would suggest that you keep a deadline task transfer
>>> count in
>>> the loop and then update cs and cpouset_attach_old_cs only after all the
>>> tasks have been iterated successfully.
>> Right, Dietmar I think commented pointing out something along these
>> lines. Think though we already have this problem with current
>> task_can_attach -> dl_cpu_busy which reserves bandwidth for each tasks
>> in the destination cs. Will need to look into that. Do you know which
>> sort of operation would move multiple tasks at once?
> 
> Actually, what I said previously may not be enough. There can be
> multiple controllers attached to a cgroup. If any of thier can_attach()
> calls fails, the whole transaction is aborted and cancel_attach() will
> be called. My new suggestion is to add a new deadline task transfer
> count into the cpuset structure and store the information there
> temporarily. If cpuset_attach() is called, it means all the can_attach
> calls succeed. You can then update the dl task count accordingly and
> clear the temporary transfer count.
> 
> I guess you may have to do something similar with dl_cpu_busy().

I gave it a shot:

https://lkml.kernel.org/r/20230322135959.1998790-1-dietmar.eggemann@arm.com