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

Jan Depner
2004-07-13T00:54:12Z

Is this problem strictly with reiserfs in 2.6 or is it also a problem
with 2.4. I actually experienced fewer xruns with reiserfs vs ext3 on
2.4 (preempt/ll) but I have no hard numbers to back that up.

Jan

On Mon, 2004-07-12 at 19:17, Lee Revell wrote:
> 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
>
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