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Wed, 15 Mar 2023 05:19:03 -0700 (PDT) Received: from localhost.localdomain.com ([2a00:23c6:4a21:6f01:ac73:9611:643a:5397]) by smtp.gmail.com with ESMTPSA id f11-20020ac8014b000000b003bd21323c80sm3672595qtg.11.2023.03.15.05.19.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Mar 2023 05:19:03 -0700 (PDT) From: Juri Lelli To: Peter Zijlstra , Ingo Molnar , Qais Yousef , Waiman Long , Tejun Heo , Zefan Li , Johannes Weiner , Hao Luo Cc: Dietmar Eggemann , Steven Rostedt , 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 , Wei Wang , Rick Yiu , Quentin Perret , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sudeep Holla , Juri Lelli Subject: [RFC PATCH 0/3] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration Date: Wed, 15 Mar 2023 12:18:09 +0000 Message-Id: <20230315121812.206079-1-juri.lelli@redhat.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1760439404873026802?= X-GMAIL-MSGID: =?utf-8?q?1760439404873026802?= 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 I instead would propose we 1 - 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) 2 - Keep track of the number of DEADLINE tasks belonging to each cpuset 3 - 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 This set is also available from https://github.com/jlelli/linux.git deadline/rework-cpusets Feedback is more than welcome. Best, Juri 1 - https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/ Juri Lelli (3): 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 ++- kernel/cgroup/cgroup.c | 4 + kernel/cgroup/cpuset.c | 175 +++++++++++++++++++++++------------------ kernel/sched/core.c | 32 ++++++-- 4 files changed, 137 insertions(+), 86 deletions(-)