linux-kernel - [PATCH] cgroup/cpuset: avoid unneeded cpuset

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Date:   Tue, 4 Jul 2023 20:03:52 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <longman@...hat.com>, <tj@...nel.org>, <hannes@...xchg.org>,
        <lizefan.x@...edance.com>
CC:     <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH] cgroup/cpuset: avoid unneeded cpuset_mutex re-lock

cpuset_mutex unlock and lock pair is only needed when transferring tasks
out of empty cpuset. Avoid unneeded cpuset_mutex re-lock when !is_empty
to save cpu cycles.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 kernel/cgroup/cpuset.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 601c40da8e03..e136269c152c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3521,17 +3521,16 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
 	is_empty = cpumask_empty(cs->cpus_allowed) ||
 		   nodes_empty(cs->mems_allowed);
 
-	mutex_unlock(&cpuset_mutex);
-
 	/*
 	 * Move tasks to the nearest ancestor with execution resources,
 	 * This is full cgroup operation which will also call back into
 	 * cpuset. Should be done outside any lock.
 	 */
-	if (is_empty)
+	if (is_empty) {
+		mutex_unlock(&cpuset_mutex);
 		remove_tasks_in_empty_cpuset(cs);
-
-	mutex_lock(&cpuset_mutex);
+		mutex_lock(&cpuset_mutex);
+	}
 }
 
 static void
-- 
2.33.0