2023-07-04 12:13:05

by Miaohe Lin

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 <[email protected]>
---
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

2023-07-05 03:45:50

by Waiman Long

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 <[email protected]>
> ---
> 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 <[email protected]>

2023-07-10 20:45:31

by Tejun Heo

Subject: Re: [PATCH] cgroup/cpuset: avoid unneeded cpuset_mutex re-lock

On Tue, Jul 04, 2023 at 08:03:52PM +0800, 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 <[email protected]>

Applied to cgroup/for-6.6.

Thanks.

--
tejun