cgroup/cpuset: Iterate only if DEADLINE tasks are present

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 <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>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ca195ff8b298b504065c9a4c6905fa9394d80b76..b7168970fff2ec47e415bbcff09703e617ccc58e 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1092,6 +1092,9 @@ 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)))