Re: [RFC PATCH 2/3] sched/cpuset: Keep track of SCHED_DEADLINE tasks in cpusets

From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Juri Lelli <juri.lelli@redhat.com>, Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>, Qais Yousef <qyousef@layalina.io>,
	Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>, Hao Luo <haoluo@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it,
	claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it,
	bristot@redhat.com, mathieu.poirier@linaro.org,
	cgroups@vger.kernel.org,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Wei Wang <wvw@google.com>, Rick Yiu <rickyiu@google.com>,
	Quentin Perret <qperret@google.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [RFC PATCH 2/3] sched/cpuset: Keep track of SCHED_DEADLINE tasks in cpusets
Date: Wed, 22 Mar 2023 14:18:47 +0100	[thread overview]
Message-ID: <c77bc281-b6e1-1653-6bed-0249f85b7e94@arm.com> (raw)
In-Reply-To: <ZBH9E7lCEXcFDBG4@localhost.localdomain>

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