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 <meltedpiano...@gmail.com> --- Remark: This patch has kind of a long history... I first tried to prevent the critical section in the wakeup() function itself by a change in the scheduler. But after review remarks from Oleg Nesterov it turned out that using the waitqueue_active() was a much nicer way to prevent it. See also https://lkml.org/lkml/2012/10/25/159 drivers/tty/tty_ldisc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index c578229..e96d187 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); } /** -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
