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Message-ID: <974a48a8-7402-6303-10e8-9d5fe475bb42@redhat.com>
Date: Tue, 4 Jul 2023 23:10:01 -0400
From: Waiman Long <longman@...hat.com>
To: Miaohe Lin <linmiaohe@...wei.com>, tj@...nel.org,
hannes@...xchg.org, lizefan.x@...edance.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup/cpuset: avoid unneeded cpuset_mutex re-lock
On 7/4/23 08:03, Miaohe Lin wrote:
> 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
Reviewed-by: Waiman Long <longman@...hat.com>
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