linux-kernel - Re: 2.6.19-rc6-rt8: alsa xruns

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Message-Id: <1164749755.15887.54.camel@cmn3.stanford.edu>
Date:	Tue, 28 Nov 2006 13:35:55 -0800
From:	Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	nando@...ma.Stanford.EDU,
	"Linux-Kernel," <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.19-rc6-rt8: alsa xruns

On Tue, 2006-11-28 at 13:04 -0800, Fernando Lopez-Lezcano wrote:
> On Tue, 2006-11-28 at 12:37 -0800, Fernando Lopez-Lezcano wrote:
> > On Tue, 2006-11-28 at 21:09 +0100, Ingo Molnar wrote:
> > > * Fernando Lopez-Lezcano <nando@...ma.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...
> 
> Strange, I rebooted smp and I'm not seeing the very long xruns I was
> seeing before, only short ones as reported above. Here are some traces,
> but nothing that makes sense I think.
> 
> I'll turn off the machine and cold boot it...)

No difference, actually it looks like the regression re-regresses if I
enable the trace... Arghhh.

Toggling /proc/sys/kernel/trace_enabled makes the long xruns reported by
jack come and go. 

-- Fernando


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