From:   Waiman Long <longman@redhat.com>
To:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shuah Khan <shuah@kernel.org>
Cc:     cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Waiman Long <longman@redhat.com>
Subject: [PATCH 1/5] cgroup/cpuset: Skip task update if hotplug doesn't affect current cpuset
Date:   Mon,  6 Mar 2023 15:08:45 -0500
Message-Id: <20230306200849.376804-2-longman@redhat.com>
In-Reply-To: <20230306200849.376804-1-longman@redhat.com>
References: <20230306200849.376804-1-longman@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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If a hotplug event doesn't affect the current cpuset, there is no point
to call hotplug_update_tasks() or hotplug_update_tasks_legacy(). So
just skip it.

Signed-off-by: Waiman Long <longman@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 636f1c682ac0..a801abad3bac 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3508,6 +3508,8 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 update_tasks:
 	cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
 	mems_updated = !nodes_equal(new_mems, cs->effective_mems);
+	if (!cpus_updated && !mems_updated)
+		goto unlock;	/* Hotplug doesn't affect this cpuset */
 
 	if (mems_updated)
 		check_insane_mems_config(&new_mems);
@@ -3519,6 +3521,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 		hotplug_update_tasks_legacy(cs, &new_cpus, &new_mems,
 					    cpus_updated, mems_updated);
 
+unlock:
 	percpu_up_write(&cpuset_rwsem);
 }
 
-- 
2.31.1