The following commit has been merged into the sched/core branch of tip:
Commit-ID: b7ca5743a2604156d6083b88cefacef983f3a3a6
Gitweb: https://git.kernel.org/tip/b7ca5743a2604156d6083b88cefacef983f3a3a6
Author: John Stultz <jstultz@google.com>
AuthorDate: Tue, 29 Apr 2025 08:07:26 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 30 Apr 2025 14:45:41 +02:00
sched/core: Tweak wait_task_inactive() to force dequeue sched_delayed tasks
It was reported that in 6.12, smpboot_create_threads() was
taking much longer then in 6.6.
I narrowed down the call path to:
smpboot_create_threads()
-> kthread_create_on_cpu()
-> kthread_bind()
-> __kthread_bind_mask()
->wait_task_inactive()
Where in wait_task_inactive() we were regularly hitting the
queued case, which sets a 1 tick timeout, which when called
multiple times in a row, accumulates quickly into a long
delay.
I noticed disabling the DELAY_DEQUEUE sched feature recovered
the performance, and it seems the newly create tasks are usually
sched_delayed and left on the runqueue.
So in wait_task_inactive() when we see the task
p->se.sched_delayed, manually dequeue the sched_delayed task
with DEQUEUE_DELAYED, so we don't have to constantly wait a
tick.
Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
Reported-by: peter-yc.chang@mediatek.com
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lkml.kernel.org/r/20250429150736.3778580-1-jstultz@google.com
---
kernel/sched/core.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 79692f8..a3507ed 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2283,6 +2283,12 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
* just go back and repeat.
*/
rq = task_rq_lock(p, &rf);
+ /*
+ * If task is sched_delayed, force dequeue it, to avoid always
+ * hitting the tick timeout in the queued case
+ */
+ if (p->se.sched_delayed)
+ dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
trace_sched_wait_task(p);
running = task_on_cpu(rq, p);
queued = task_on_rq_queued(p);