Re: [bisected] pty performance problem
From: Alan Cox
Date: Mon Nov 23 2009 - 08:32:44 EST
> > 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.
Alan
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