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

[Jan Depner]

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 at 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
> 
> 
> 
> 
>