Re: 2.6.19-rc6-rt8: alsa xruns

[Fernando Lopez-Lezcano <nando@ccrma.Stanford.EDU>]

On Tue, 2006-11-28 at 21:09 +0100, Ingo Molnar wrote:
> * Fernando Lopez-Lezcano <nando@ccrma.Stanford.EDU> wrote:
> 
> > Hi, I'm trying out the latest -rt patch and getting alsa xruns when 
> > using jackd and jack clients. This is a sample from the output of 
> > qjackctl / jackd (jack 0.102.25, qjackctl 0.2.21):
> 
> > (            japa-4096 |#0): new 17 us maximum-latency wakeup.
> > (         beagled-3412 |#1): new 19 us maximum-latency wakeup.
> > (          IRQ 18-1081 |#1): new 26 us maximum-latency wakeup.
> > (             snd-4040 |#1): new 1107 us maximum-latency wakeup.
> > (            japa-4096 |#0): new 1445 us maximum-latency wakeup.
> > (            japa-4096 |#0): new 2110 us maximum-latency wakeup.
> > (        qjackctl-4038 |#1): new 2328 us maximum-latency wakeup.
> > (            japa-4096 |#0): new 2548 us maximum-latency wakeup.
> > (          IRQ 18-1081 |#0): new 10291 us maximum-latency wakeup.
> 
> hm, lets fix this. Could you enable tracing (on the yum rpm) via:
> 
> 	echo 1 > /proc/sys/kernel/trace_enabled
> 
> does /proc/latency_trace have any meaningful events included for such a 
> long delay? If not then it would be nice to rebuild the kernel with 
> CONFIG_LATENCY_TRACING - and in any case my previous suggestion holds 
> too: booting with maxcpus=1 to reproduce the latencies will give easier 
> to interpret latency traces. 

Sorry, it looks like it is an smp issue. Booting with maxcpus=1 reduces
the xrun reports significantly (only three so far but very short, in the
range of 0.029 to 0.041 ms). The long ones seem to have gone away, so
far...

> (but if it's SMP-only then no problem, the 
> latency traces are still valuable)

-- Fernando