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tty: Only wakeup the line discipline idle queue when queue is active

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ivo Sieben 2012-12-18 15:48:50 +01:00 committed by Greg Kroah-Hartman
parent b342dd512f
commit bd5d7ce9af
1 changed files with 3 additions and 1 deletions
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4
drivers/tty/tty_ldisc.c
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@ -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);
}
/**