[PATCH 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present

From: Qais Yousef
Date: Sun Aug 20 2023 - 11:25:09 EST


From: Juri Lelli <juri.lelli@xxxxxxxxxx>

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@xxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@xxxxxxxxxxx/
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
(cherry picked from commit c0f78fd5edcf29b2822ac165f9248a6c165e8554)
Signed-off-by: Qais Yousef (Google) <qyousef@xxxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 5f57829bb986..eca07ff71656 100644
--- 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)))
--
2.34.1