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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>,
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        Hao Luo <haoluo@google.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
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        Vincent Guittot <vincent.guittot@linaro.org>,
        Wei Wang <wvw@google.com>, Rick Yiu <rickyiu@google.com>,
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        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 6/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present
Date:   Wed, 29 Mar 2023 14:55:58 +0200
Message-Id: <20230329125558.255239-7-juri.lelli@redhat.com>
In-Reply-To: <20230329125558.255239-1-juri.lelli@redhat.com>
References: <20230329125558.255239-1-juri.lelli@redhat.com>
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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 <qyousef@layalina.io>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 kernel/cgroup/cpuset.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index f8ebec66da51..05c0a1255218 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)))
-- 
2.39.2