Patch "cgroup/cpuset: Iterate only if DEADLINE tasks are present" has been added to the 6.4-stable tree

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This is a note to let you know that I've just added the patch titled

    cgroup/cpuset: Iterate only if DEADLINE tasks are present

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cgroup-cpuset-iterate-only-if-deadline-tasks-are-present.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From stable-owner@xxxxxxxxxxxxxxx Tue Aug 22 00:20:47 2023
From: Qais Yousef <qyousef@xxxxxxxxxxx>
Date: Mon, 21 Aug 2023 23:19:54 +0100
Subject: cgroup/cpuset: Iterate only if DEADLINE tasks are present
To: stable@xxxxxxxxxxxxxxx
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>, Waiman Long <longman@xxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Dietmar Eggemann <dietmar.eggemann@xxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Vincent Guittot <vincent.guittot@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Hao Luo <haoluo@xxxxxxxxxx>, John Stultz <jstultz@xxxxxxxxxx>, cgroups@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Qais Yousef <qyousef@xxxxxxxxxxx>
Message-ID: <20230821221956.698117-5-qyousef@xxxxxxxxxxx>

From: Juri Lelli <juri.lelli@xxxxxxxxxx>

commit c0f78fd5edcf29b2822ac165f9248a6c165e8554 upstream.

update_tasks_root_domain currently iterates over all tasks even if no
DEADLINE task is present on the cpuset/root domain for which bandwidth
accounting is being rebuilt. This has been reported to introduce 10+ ms
delays on suspend-resume operations.

Skip the costly iteration for cpusets that don't contain DEADLINE tasks.

Reported-by: Qais Yousef (Google) <qyousef@xxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@xxxxxxxxxxx/
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Qais Yousef (Google) <qyousef@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/cgroup/cpuset.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1092,6 +1092,9 @@ static void dl_update_tasks_root_domain(
 	struct css_task_iter it;
 	struct task_struct *task;
 
+	if (cs->nr_deadline_tasks == 0)
+		return;
+
 	css_task_iter_start(&cs->css, 0, &it);
 
 	while ((task = css_task_iter_next(&it)))


Patches currently in stable-queue which might be from stable-owner@xxxxxxxxxxxxxxx are

queue-6.4/cgroup-cpuset-free-dl-bw-in-case-can_attach-fails.patch
queue-6.4/sched-cpuset-keep-track-of-sched_deadline-task-in-cpusets.patch
queue-6.4/cgroup-cpuset-rename-functions-dealing-with-deadline-accounting.patch
queue-6.4/cgroup-cpuset-iterate-only-if-deadline-tasks-are-present.patch
queue-6.4/sched-cpuset-bring-back-cpuset_mutex.patch
queue-6.4/sched-deadline-create-dl-bw-alloc-free-check-overflow-interface.patch



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