linux-kernel - [PATCH 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present

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Message-Id: <20230821221956.698117-5-qyousef@layalina.io>
Date:   Mon, 21 Aug 2023 23:19:54 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     stable@...r.kernel.org
Cc:     Juri Lelli <juri.lelli@...hat.com>,
        Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...nel.org>, Hao Luo <haoluo@...gle.com>,
        John Stultz <jstultz@...gle.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, Qais Yousef <qyousef@...alina.io>
Subject: [PATCH 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present

From: Juri Lelli <juri.lelli@...hat.com>

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@...alina.io>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
Reviewed-by: Waiman Long <longman@...hat.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
(cherry picked from commit c0f78fd5edcf29b2822ac165f9248a6c165e8554)
Signed-off-by: Qais Yousef (Google) <qyousef@...alina.io>
---
 kernel/cgroup/cpuset.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ca195ff8b298..b7168970fff2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1092,6 +1092,9 @@ static void dl_update_tasks_root_domain(struct cpuset *cs)
 	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)))
-- 
2.34.1