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From:   Juri Lelli <juri.lelli@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Qais Yousef <qyousef@layalina.io>,
        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>
Cc:     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>,
        Juri Lelli <juri.lelli@redhat.com>
Subject: [PATCH 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration
Date:   Wed, 29 Mar 2023 14:55:52 +0200
Message-Id: <20230329125558.255239-1-juri.lelli@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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(-)

-- 
2.39.2