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author | Linus Torvalds <torvalds@linux-foundation.org> | 2011-03-22 23:17:32 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-03-22 23:17:32 (GMT) |
commit | f23eb2b2b28547fc70df82dd5049eb39bec5ba12 (patch) | |
tree | 144dce462b34d8a232a06f766786ebfb0235fa87 /drivers/tty/tty_ldisc.c | |
parent | f741a79e982cf56d7584435bad663553ffe6715f (diff) | |
download | linux-f23eb2b2b28547fc70df82dd5049eb39bec5ba12.tar.xz |
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 <jefdriesen@telenet.be>
Acked-by: Greg KH <gregkh@suse.de>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/tty/tty_ldisc.c')
-rw-r--r-- | drivers/tty/tty_ldisc.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 0fc564a..e19e136 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(); |