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SubjectRe: [bisected] pty performance problem

* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> > > So you'd prefer to detect devices that are byte based or message based
> > > by what method ?
> >
> > I'd not delay the worklet by default - i.e. i'd do Mike's patch.
>
> Certainly stuff like pty should not delay
> >
> > Havent tested all effects of it though - do you have any estimation
> > about negative effects from such a change? We do have hard numbers
> > (latencies in the millisecs range) from the opposite direction and those
> > numbers arent pretty.
>
> On a PC I'm not too worried - we might burn a bit more CPU and Arjan
> might even manage to measure it somewhere. There is the theoretical bad
> case where we end up at 100% CPU because the irq, wake, process one char,
> irq wake, process one char sequence fits the CPU so we don't sleep.
>
> Embedded might be more of a concern, the old behaviour comes from 386/486
> days with low CPU power.
>
> USB doesn't worry me - USB devices generally have their own buffering
> algorithm and use a timer so that they batch data efficiently into USB
> buffers.
>
> The drivers/serial layer is often run with low latency set anyway so that
> seems to be ok for the most part.
>
> Give it a go, send the patch to the maintainer, try it in -next and see
> if anyone screams.

(Doh, i should have Cc:-ed Greg first time around - fixed that.)

Ingo


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