From 3afb1b394a49d1237c9c0af8e8b724ddfe5b94ba Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Tue, 23 Jul 2013 08:47:30 -0400 Subject: [PATCH] n_tty: Special case pty flow control The pty driver forces ldisc flow control on, regardless of available receive buffer space, so the writer can be woken whenever unthrottle is called. However, this 'forced throttle' has performance consequences, as multiple atomic operations are necessary to unthrottle and perform the write wakeup for every input line (in canonical mode). Instead, short-circuit the unthrottle if the tty is a pty and perform the write wakeup directly. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_tty.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 0e3efc1..59eb444 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -231,6 +231,8 @@ static void n_tty_write_wakeup(struct tty_struct *tty) static inline void n_tty_check_throttle(struct tty_struct *tty) { + if (tty->driver->type == TTY_DRIVER_TYPE_PTY) + return; /* * Check the remaining room for the input canonicalization * mode. We don't want to throttle the driver if we're in @@ -250,6 +252,18 @@ static inline void n_tty_check_throttle(struct tty_struct *tty) static inline void n_tty_check_unthrottle(struct tty_struct *tty) { + if (tty->driver->type == TTY_DRIVER_TYPE_PTY && + tty->link->ldisc->ops->write_wakeup == n_tty_write_wakeup) { + if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE) + return; + if (!tty->count) + return; + n_tty_set_room(tty); + n_tty_write_wakeup(tty->link); + wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT); + return; + } + /* If there is enough space in the read buffer now, let the * low-level driver know. We use chars_in_buffer() to * check the buffer, as it now knows about canonical mode. -- 2.7.4