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

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Message-Id: <20230508075854.17215-1-juri.lelli@redhat.com>
Date:   Mon,  8 May 2023 09:58:48 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>,
        Waiman Long <longman@...hat.com>, 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>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: [PATCH v3 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

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

Best,
Juri

1 - https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
2 - RFC https://lore.kernel.org/lkml/20230315121812.206079-1-juri.lelli@redhat.com/
3 - v1  https://lore.kernel.org/lkml/20230329125558.255239-1-juri.lelli@redhat.com/
4 - v2  https://lore.kernel.org/lkml/20230503072228.115707-1-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  | 244 ++++++++++++++++++++++++++--------------
 kernel/sched/core.c     |  41 +++----
 kernel/sched/deadline.c |  67 ++++++++---
 kernel/sched/sched.h    |   2 +-
 7 files changed, 246 insertions(+), 128 deletions(-)

-- 
2.40.1