6.15-stable review patch. If anyone has any objections, please let me know.
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From: John Stultz jstultz@google.com
[ Upstream commit b7ca5743a2604156d6083b88cefacef983f3a3a6 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 36b34e6884587..d593d6612ba07 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);