[linux-audio-user] Which kernel for low latency and kernel 2.6.1-mm# problems

Steve Harris S.W.Harris at ecs.soton.ac.uk
Wed Jan 21 06:15:11 EST 2004

On Wed, Jan 21, 2004 at 03:01:19 -0800, Andrew Morton wrote:
> > I just wanted to elaborate abit; -R in the argument line indicates that jack 
> > should be running SCHED_FIFO, and since there are no specific settings for 
> > period-size and number of periods, jack is probably defaulting to 2-periods 
> > and 1024 samples period size. 2.4 works rather reliably with period-sizes 
> > quite a bit smaller than that. I think 256 is commonly used, with good 
> > hardware+drivers I suppose you could go even lower.
> I don't know what these numbers mean...
> What does this transalate to in interval-in-milliseconds, and after how
> many milliseconds delay will an underrun occur?

The default sampe rate is 48kHz, so 1024 samples/block gives 21ms between
interupts. Jack easts a bit of that, but you'd have ~20ms before an
underrun occured.

> And what else is happening on the system at the time?

The original poster would have to anwer that. Jack itsself is just messing
with SYSV SHM and occasioanly touching fifos.

As someone else said, jack runs reliably on most 2.4+ll+o(1)sched systems
with 5ms (256 sample) interupt fequencies and usually lower.

- Steve

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