Messages in this thread Patch in this message |  | | From | Ivo Sieben <> | Subject | [PATCH] tty: Only wakeup the line discipline idle queue when queue is active | Date | Tue, 18 Dec 2012 15:48:50 +0100 |
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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> ---
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
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