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

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Date:   Wed, 29 Mar 2023 10:34:57 -0400
From:   Waiman Long <longman@...hat.com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>
Cc:     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 3/29/23 08:55, 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
>
> Best,
> Juri
>
> 1 - https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
> 2 - https://lore.kernel.org/lkml/20230315121812.206079-1-juri.lelli@redhat.com/
>
> Dietmar Eggemann (2):
>    sched/deadline: Create DL BW alloc, free & check overflow interface
>    cgroup/cpuset: Free DL BW in case can_attach() fails
>
> Juri Lelli (4):
>    cgroup/cpuset: Rename functions dealing with DEADLINE accounting
>    sched/cpuset: Bring back cpuset_mutex
>    sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
>    cgroup/cpuset: Iterate only if DEADLINE tasks are present
>
>   include/linux/cpuset.h  |  12 ++-
>   include/linux/sched.h   |   4 +-
>   kernel/cgroup/cgroup.c  |   4 +
>   kernel/cgroup/cpuset.c  | 232 ++++++++++++++++++++++++++--------------
>   kernel/sched/core.c     |  41 ++++---
>   kernel/sched/deadline.c |  67 +++++++++---
>   kernel/sched/sched.h    |   2 +-
>   7 files changed, 240 insertions(+), 122 deletions(-)

Other than some minor issues that I have talked in earlier emails, the 
patch series looks good to me.

You can add my ack once the issues are fixed.

Acked-by: Waiman Long <longman@...hat.com>