linux-kernel - Re: [PATCH 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

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Date:   Tue, 18 Apr 2023 10:31:27 -0400
From:   Waiman Long <longman@...hat.com>
To:     Qais Yousef <qyousef@...alina.io>,
        Juri Lelli <juri.lelli@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....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: [PATCH 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth
 restoration

On 4/18/23 10:11, Qais Yousef wrote:
> On 03/29/23 14:55, Juri Lelli wrote:
>> Qais reported [1] that iterating over all tasks when rebuilding root
>> domains for finding out which ones are DEADLINE and need their bandwidth
>> correctly restored on such root domains can be a costly operation (10+
>> ms delays on suspend-resume). He proposed we skip rebuilding root
>> domains for certain operations, but that approach seemed arch specific
>> and possibly prone to errors, as paths that ultimately trigger a rebuild
>> might be quite convoluted (thanks Qais for spending time on this!).
>>
>> To fix the problem
>>
>>   01/06 - Rename functions deadline with DEADLINE accounting (cleanup
>>           suggested by Qais) - no functional change
>>   02/06 - Bring back cpuset_mutex (so that we have write access to cpusets
>>           from scheduler operations - and we also fix some problems
>>           associated to percpu_cpuset_rwsem)
>>   03/06 - Keep track of the number of DEADLINE tasks belonging to each cpuset
>>   04/06 - Create DL BW alloc, free & check overflow interface for bulk
>>           bandwidth allocation/removal - no functional change
>>   05/06 - Fix bandwidth allocation handling for cgroup operation
>>           involving multiple tasks
>>   06/06 - Use this information to only perform the costly iteration if
>>           DEADLINE tasks are actually present in the cpuset for which a
>>           corresponding root domain is being rebuilt
>>
>> With respect to the RFC posting [2]
>>
>>   1 - rename DEADLINE bandwidth accounting functions - Qais
>>   2 - call inc/dec_dl_tasks_cs from switched_{to,from}_dl - Qais
>>   3 - fix DEADLINE bandwidth allocation with multiple tasks - Waiman,
>>       contributed by Dietmar
>>
>> This set is also available from
>>
>> https://github.com/jlelli/linux.git deadline/rework-cpusets
> Is this just waiting to be picked up or still there's something to be addressed
> still?

There are some changes to cpuset code recently and so I believe that 
this patch series may need to be refreshed to reconcile the changes.

Thanks,
Longman