From f23eb2b2b28547fc70df82dd5049eb39bec5ba12 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 22 Mar 2011 16:17:32 -0700 Subject: tty: stop using "delayed_work" in the tty layer Using delayed-work for tty flip buffers ends up causing us to wait for the next tick to complete some actions. That's usually not all that noticeable, but for certain latency-critical workloads it ends up being totally unacceptable. As an extreme case of this, passing a token back-and-forth over a pty will take two ticks per iteration, so even just a thousand iterations will take 8 seconds assuming a common 250Hz configuration. Avoiding the whole delayed work issue brings that ping-pong test-case down to 0.009s on my machine. In more practical terms, this latency has been a performance problem for things like dive computer simulators (simulating the serial interface using the ptys) and for other environments (Alan mentions a CP/M emulator). Reported-by: Jef Driesen Acked-by: Greg KH Acked-by: Alan Cox Signed-off-by: Linus Torvalds --- drivers/tty/tty_ldisc.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'drivers/tty/tty_ldisc.c') diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 0fc564a97706..e19e13647116 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -529,7 +529,7 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old) static int tty_ldisc_halt(struct tty_struct *tty) { clear_bit(TTY_LDISC, &tty->flags); - return cancel_delayed_work_sync(&tty->buf.work); + return cancel_work_sync(&tty->buf.work); } /** @@ -542,7 +542,7 @@ static void tty_ldisc_flush_works(struct tty_struct *tty) { flush_work_sync(&tty->hangup_work); flush_work_sync(&tty->SAK_work); - flush_delayed_work_sync(&tty->buf.work); + flush_work_sync(&tty->buf.work); } /** @@ -722,9 +722,9 @@ enable: /* Restart the work queue in case no characters kick it off. Safe if already running */ if (work) - schedule_delayed_work(&tty->buf.work, 1); + schedule_work(&tty->buf.work); if (o_work) - schedule_delayed_work(&o_tty->buf.work, 1); + schedule_work(&o_tty->buf.work); mutex_unlock(&tty->ldisc_mutex); tty_unlock(); return retval; @@ -830,12 +830,12 @@ void tty_ldisc_hangup(struct tty_struct *tty) /* * this is like tty_ldisc_halt, but we need to give up - * the BTM before calling cancel_delayed_work_sync, - * which may need to wait for another function taking the BTM + * the BTM before calling cancel_work_sync, which may + * need to wait for another function taking the BTM */ clear_bit(TTY_LDISC, &tty->flags); tty_unlock(); - cancel_delayed_work_sync(&tty->buf.work); + cancel_work_sync(&tty->buf.work); mutex_unlock(&tty->ldisc_mutex); tty_lock(); -- cgit v1.2.3