Commit 3afb1b39 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman

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: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ee0bab83
...@@ -231,6 +231,8 @@ static void n_tty_write_wakeup(struct tty_struct *tty) ...@@ -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) 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 * Check the remaining room for the input canonicalization
* mode. We don't want to throttle the driver if we're in * 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) ...@@ -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) 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 /* If there is enough space in the read buffer now, let the
* low-level driver know. We use chars_in_buffer() to * low-level driver know. We use chars_in_buffer() to
* check the buffer, as it now knows about canonical mode. * check the buffer, as it now knows about canonical mode.
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment