From bd5d7ce9afdd0cddc5ab65e20d1134ccad824418 Mon Sep 17 00:00:00 2001 From: Ivo Sieben Date: Tue, 18 Dec 2012 15:48:50 +0100 Subject: tty: Only wakeup the line discipline idle queue when queue is active Before waking up the tty line discipline idle queue first check if the queue is active (non empty). This prevents unnecessary entering the critical section in the wake_up() function and therefore avoid needless scheduling overhead on a PREEMPT_RT system caused by two processes being in the same critical section. Signed-off-by: Ivo Sieben Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldisc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'drivers') diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index c5782294e53..e96d1876bd6 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -64,7 +64,9 @@ static void put_ldisc(struct tty_ldisc *ld) return; } raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); - wake_up(&ld->wq_idle); + + if (waitqueue_active(&ld->wq_idle)) + wake_up(&ld->wq_idle); } /** -- cgit v1.2.3-70-g09d2