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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 79692f85643fee05ac1f1ed5d6ef08e807a29c55..a3507ed58424f2874e4a6ba99b2b21ba6562f67f 100644 (file)
--- 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);