On 12/18/2012 03:48 PM, Ivo Sieben wrote: > 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@xxxxxxxxx> > --- > > 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); Looks good, but I would prefer the layer to provide us with wake_up_if_active... -- js suse labs -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
