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    SubjectRe: [bisected] pty performance problem
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    On Sun, 2009-11-22 at 12:23 +0000, Alan Cox wrote:
    > On Sun, 22 Nov 2009 07:39:26 +0100
    > Ingo Molnar <mingo@elte.hu> 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)
    flush_to_ldisc(&tty->buf.work.work);
    else
    - schedule_delayed_work(&tty->buf.work, 1);
    + schedule_delayed_work(&tty->buf.work, 0);
    }
    EXPORT_SYMBOL(tty_flip_buffer_push);

    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?
    -Mike



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