From: Steven Rostedt Date: Mon, 18 Mar 2013 15:12:49 -0400 Subject: [PATCH 113/351] sched/workqueue: Only wake up idle workers if not blocked on sleeping spin lock Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=eb80c24da74db0be170d2e19868ad5eb355a27b0 In -rt, most spin_locks() turn into mutexes. One of these spin_lock conversions is performed on the workqueue gcwq->lock. When the idle worker is worken, the first thing it will do is grab that same lock and it too will block, possibly jumping into the same code, but because nr_running would already be decremented it prevents an infinite loop. But this is still a waste of CPU cycles, and it doesn't follow the method of mainline, as new workers should only be woken when a worker thread is truly going to sleep, and not just blocked on a spin_lock(). Check the saved_state too before waking up new workers. Signed-off-by: Steven Rostedt Signed-off-by: Sebastian Andrzej Siewior --- kernel/sched/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b375f10ca8f8..54f22c835740 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3544,8 +3544,10 @@ static void __sched notrace __schedule(bool preempt) * If a worker went to sleep, notify and ask workqueue * whether it wants to wake up a task to maintain * concurrency. + * Only call wake up if prev isn't blocked on a sleeping + * spin lock. */ - if (prev->flags & PF_WQ_WORKER) { + if (prev->flags & PF_WQ_WORKER && !prev->saved_state) { struct task_struct *to_wakeup; to_wakeup = wq_worker_sleeping(prev);