Messages in this thread | | | Date | Sat, 23 Nov 2013 21:29:17 -0500 | From | Peter Hurley <> | Subject | Re: [PATCH tty-next 6/7] n_tty: Only perform wakeups for waiters |
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On 11/23/2013 07:23 PM, One Thousand Gnomes wrote: > On Fri, 22 Nov 2013 10:59:24 -0500 > Peter Hurley <peter@hurleysoftware.com> wrote: > >> Only wakeup the _waiting_ reader, polls and/or writer(s). >> >> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> >> --- >> drivers/tty/n_tty.c | 18 ++++++++++++------ >> 1 file changed, 12 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c >> index 8f2356e..aae28a6 100644 >> --- a/drivers/tty/n_tty.c >> +++ b/drivers/tty/n_tty.c >> @@ -275,7 +275,8 @@ static void n_tty_check_unthrottle(struct tty_struct *tty) >> return; >> n_tty_set_room(tty); >> n_tty_write_wakeup(tty->link); >> - wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT); >> + if (waitqueue_active(&tty->link->write_wait)) >> + wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT); > > Does this actually microbenchmark faster ?
Getting on and off the write_wait queue is actually pretty expensive for the "other" pty (the writer), and the unnecessary wakeup from the reader doesn't help.
The other chunks are gratuitous.
Regards, Peter Hurley
PS - This came up because there is some worst-case behavior that I'm looking into fixing. When the userspace reader is very far behind (say because it's reading char-by-char), it doesn't make sense to keep restarting the input processing worker.
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