linux-kernel - Re: [PATCH v3 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

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Message-ID: <ZFmEoBoX15FIpyW1@slm.duckdns.org>
Date:   Mon, 8 May 2023 13:24:16 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>,
        Waiman Long <longman@...hat.com>,
        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 v3 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth
 restoration

On Mon, May 08, 2023 at 09:58:48AM +0200, 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!).
> 
> This is v3 of an alternative approach (v2 at [4]) 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 - 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
>  05/06 - Create DL BW alloc, free & check overflow interface for bulk
>          bandwidth allocation/removal - no functional change 
>  06/06 - Fix bandwidth allocation handling for cgroup operation
>          involving multiple tasks
> 
> With respect to the v2 posting [4]
> 
>  1 - rebase on top of Linus' tree as of today (ac9a78681b92)
>  2 - add the 'why' to 5/6 changelog - Peter
>  3 - explicitly say that we need to keep cpuset_mutex a mutex for PI on
>      2/6 - Peter
> 
> This set is also available from
> 
> https://github.com/jlelli/linux.git deadline/rework-cpusets

Applied to cgroup/for-6.5.

Thanks.

-- 
tejun