Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

Lee Revell
2004-07-13T00:17:36Z

On Mon, 2004-07-12 at 19:31, Andrew Morton wrote:
> Lee Revell <rlrevell@joe-job.com> wrote:
> >
> > On Sun, 2004-07-11 at 01:25, Andrew Morton wrote:
> > > What we need to do is to encourage audio testers to use ALSA drivers, to
> > > enable CONFIG_SND_DEBUG in the kernel build and to set
> > > /proc/asound/*/*/xrun_debug and to send us the traces which result from
> > > underruns.
> > >
> >
> > OK, here goes. The following traces result from running JACK overnight
> > like so, on an otherwise idle system. Hardware is a VIA EPIA 6000, with
> > a 600Mhz C3 processor. Kernel is 2.6.7 + volunatary_preempt patch.
> > voluntary_preempt and kernel_preemption are both on.
> >
> > jackd -v --realtime -d alsa --outchannels 2 --rate 48000 --shorts
> > --playback --period 32 --nperiods 2
> >
> > These settings require less than 666 microseconds scheduler latency.
> > The average performance is quite good - 5-20 *microseconds*!
>
> OK, thanks. The problem areas there are the timer-based route cache
> flushing and reiserfs.
>
> We can probably fix the route caceh thing by rescheduling the timer after
> having handled 1000 routes or whatever, although I do wonder if this is a
> thing we really need to bother about - what else was that machine up to?
>

Gnutella client. Forgot about that. I agree, it is not reasonable to
expect low latency with this kind of network traffic happening. I am
impressed it worked as well as it did.

> resierfs: yes, it's a problem. I "fixed" it multiple times in 2.4, but the
> fixes ended up breaking the fs in subtle ways and I eventually gave up.
>

Interesting. There is an overwhelming consensus amongst Linux audio
folks that you should use reiserfs for low latency work. Should I try
ext3?

Lee