linux-kernel - Re: [PATCH v3] sched: cpuset: Don't rebuild root domains on suspend-resume

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Date:   Mon, 13 Mar 2023 13:37:48 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Qais Yousef <qyousef@...alina.io>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, tj@...nel.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>,
        Zefan Li <lizefan.x@...edance.com>, linux-s390@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v3] sched: cpuset: Don't rebuild root domains on
 suspend-resume

On 08/03/2023 11:19, Juri Lelli wrote:
> On 01/03/23 17:03, Qais Yousef wrote:
>> On 03/01/23 15:26, Juri Lelli wrote:
>>> On 01/03/23 12:28, Qais Yousef wrote:
>>>> On 03/01/23 08:31, Juri Lelli wrote:
>>>
>>> ...
>>>
>>>>> Not ignoring you guys here, but it turns out I'm quite bogged down with
>>>>> other stuff at the moment. :/ So, apologies and I'll try to get to this
>>>>> asap. Thanks a lot for all your efforts and time reviewing so far!
>>>>
>>>> Np, I can feel you :-)
>>>
>>> Eh. :/
>>
>> I hope I did not offend. That was meant as no pressure, I understand.
> 
> No offence at all! I meant "we are all on the same boat it seems". :)
> 
>>> BTW, do you have a repro script of some sort handy I might play with?
>>
>> Sorry no. You'll just need to suspend to ram. I had a simple patch to measure
>> the time around the call and trace_printk'ed the result.
>>
>> I was working on a android phone which just suspends to ram if you turn the
>> screen off and disconnect the usb.
> 
> Looks like I could come up with the following
> 
> https://github.com/jlelli/linux.git deadline/rework-cpusets
> https://github.com/jlelli/linux/tree/deadline/rework-cpusets
> 
> which I don't think it's at a point that I feel comfortable to propose
> as an RFC (not even sure if it actually makes sense), but it survived my
> very light testing.
> 
> Could you please take a look and, if it makes some sense in theory, give
> it a try on your end?

sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets

@@ -2474,6 +2494,11 @@ static int cpuset_can_attach(struct
cgroup_taskset *tset)
                        goto out_unlock;
        }

+       if (dl_task(task)) {
+               cs->deadline_tasks++;
+               cpuset_attach_old_cs->deadline_tasks--;
+       }
+

This one looks odd. task is NULL here ?

If you move a DL task from one cpuset to another this happens now:

root@...o:~# ps2 | grep DLN
   82    82 140      0   - DLN sugov:0
   83    83 140      0   - DLN sugov:1
 1615  1616 140      0   - DLN thread0-0
 1615  1617 140      0   - DLN thread0-1
 1615  1618 140      0   - DLN thread0-2
 1615  1619 140      0   - DLN thread0-3
 1615  1620 140      0   - DLN thread0-4
 1615  1621 140      0   - DLN thread0-5
 1615  1622 140      0   - DLN thread0-6
 1615  1623 140      0   - DLN thread0-7
 1615  1624 140      0   - DLN thread0-8
 1615  1625 140      0   - DLN thread0-9
 1615  1626 140      0   - DLN thread0-10
 1615  1627 140      0   - DLN thread0-11 <--

root@...o:~# cd /sys/fs/cgroup/cpuset
root@...o:~# mkdir cs1
root@...o:~# echo 0 > cs1/cpuset.mems
root@...o:~# echo 0,3-5 > cs1/cpuset.cpus

root@...o:~# echo 1627 > cs1/tasks

root@...o:~# [  154.968900] *** task=0000000000000000

[...]