On 11/23/2013 07:23 PM, One Thousand Gnomes wrote:
On Fri, 22 Nov 2013 10:59:24 -0500
Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote:
Only wakeup the _waiting_ reader, polls and/or writer(s).
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
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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