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

[Andrew Morton]

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?

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.