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SubjectRe: [bisected] pty performance problem
On Sun, 2009-11-22 at 12:23 +0000, Alan Cox wrote:
> On Sun, 22 Nov 2009 07:39:26 +0100
> Ingo Molnar <> wrote:
> >
> > (Cc:-ed Alan and Linus - mail repeated below. eot.)
> I saw it and replied already. The kernel now queues the work for the pty
> as it does normal tty devices. If the CPU load is that low and nothing
> else is happening it makes me wonder what the scheduler thinks it is
> doing ?

Hm. Looks to me like it's doing what it was told to do.

diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
index 66fa4e1..92a0864 100644
--- a/drivers/char/tty_buffer.c
+++ b/drivers/char/tty_buffer.c
@@ -495,7 +495,7 @@ void tty_flip_buffer_push(struct tty_struct *tty)
if (tty->low_latency)
- schedule_delayed_work(&tty->, 1);
+ schedule_delayed_work(&tty->, 0);

Telling it to execute now made test proggy happy.. and likely broke tons
of things that need a delay there. So, what's wrong with delaying, when
that's what the customer asked for? /me must be missing something. It
could know that no delay is needed?

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