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Date:   Tue, 4 Apr 2023 21:09:09 +0100
From:   Qais Yousef <qyousef@layalina.io>
To:     Juri Lelli <juri.lelli@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Waiman Long <longman@redhat.com>, 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
Message-ID: <20230404200909.krwq36nx36ktm2sh@airbuntu>
References: <20230329125558.255239-1-juri.lelli@redhat.com>
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In-Reply-To: <20230329125558.255239-1-juri.lelli@redhat.com>
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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

Thanks a lot Juri!

I picked up the updated series and applied them to a 5.10 kernel and tested the
issue is fixed. Replied with my reviewed-and-tested-bys to some of the patches
already.

I haven't looked much at Dietmar's patches and while they were part of the
test, but there are no dl tasks on the system so I felt hesitant to say
I tested that part.


Cheers

--
Qais Yousef