linux-kernel - Re: [bisected] pty performance problem

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Message-ID: <20091123120409.GA32009@elte.hu>
Date:	Mon, 23 Nov 2009 13:04:09 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Mike Galbraith <efault@....de>, Robert Swan <swan.r.l@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [bisected] pty performance problem


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

> > > Another possibility is to do
> > > 
> > > 	if (tty->low_latency)
> > > 		schedule_delayed_work(&tty->buf.work, 0);
> > > 	else
> > > 		schedule_delayed_work(&tty->buf.work, 1);
> > 
> > Flaggery for low latency is kind of lame though - especially if it 
> > defaults to off in most drivers as you say.
> 
> 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.

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.

	Ingo
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