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Date:   Thu, 20 Apr 2023 16:15:33 +0200
From:   Juri Lelli <juri.lelli@redhat.com>
To:     Waiman Long <longman@redhat.com>
Cc:     Qais Yousef <qyousef@layalina.io>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, Tejun Heo <tj@kernel.org>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Hao Luo <haoluo@google.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.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: [PATCH 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth
 restoration
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References: <20230329125558.255239-1-juri.lelli@redhat.com>
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 <eda74c03-bde2-bb51-2b0d-df2097215696@redhat.com>
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On 18/04/23 10:31, Waiman Long wrote:
> 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.

Yeah, will soon take a look.

Thanks!
Juri