Commit bd5d7ce9 authored Dec 18, 2012 by Ivo Sieben Committed by Greg Kroah-Hartman Jan 15, 2013

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 <meltedpianoman@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b342dd51

drivers/tty/tty_ldisc.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -64,6 +64,8 @@ static void put_ldisc(struct tty_ldisc *ld)
		return;
		}
		raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);

		if (waitqueue_active(&ld->wq_idle))
		wake_up(&ld->wq_idle);
		}