cgroup/cpuset: Iterate only if DEADLINE tasks are present

commit c0f78fd5edcf29b2822ac165f9248a6c165e8554 upstream.

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 (Google) <qyousef@layalina.io>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index fa8684c790a9e009682499dd12cb9dda0a55c8de..6c69e715b05a8b0a1d88f72463609c25169d8ec5 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -937,6 +937,9 @@ 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)))