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

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Date:   Wed, 22 Mar 2023 14:18:47 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Waiman Long <longman@...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 18:14, 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?

Moving the process instead of the individual tasks makes
cpuset_can_attach() have to deal with multiple tasks.

# ps2 | grep DLN
 1614  1615 140      0   - DLN thread0-0
 1614  1616 140      0   - DLN thread0-1
 1614  1617 140      0   - DLN thread0-2

# echo 1614 > /sys/fs/cgroup/cpuset/cs2/cgroup.procs