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

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Date:	Tue, 28 Nov 2006 15:22:58 -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 13:35 -0800, Fernando Lopez-Lezcano wrote:
> 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. 

I still get long xruns with the trace on, but it does not look like it
says anything important:

----
preemption latency trace v1.1.5 on 2.6.18-1.0001.3.rt8.fc6.ccrma
--------------------------------------------------------------------
 latency: 4283 us, #8/8, CPU#0 | (M:rt VP:0, KP:0, SP:1 HP:1 #P:2)
    -----------------
    | task: IRQ 18-819 (uid:0 nice:-5 policy:1 rt_prio:70)
    -----------------

                 _------=> CPU#            
                / _-----=> irqs-off        
               | / _----=> need-resched    
               || / _---=> hardirq/softirq 
               ||| / _--=> preempt-depth   
               |||| /                      
               |||||     delay             
   cmd     pid ||||| time  |   caller      
      \   /    |||||   \   |   /           
  <idle>-0     1Dn.3 4270us+: trace_change_sched_cpu (0 1 0)
  <idle>-0     1Dn.3 4273us : deactivate_task <<...>-819> (170 2)
  <idle>-0     1Dn.3 4275us : __activate_task <<...>-819> (170 1)
   <...>-819   1D..2 4278us : thread_return <<idle>-0> (20 170)
   <...>-819   1D..1 4280us+: trace_stop_sched_switched <<...>-819> (29
1)
   <...>-819   1...1 4283us : thread_return (thread_return)


vim:ft=help
----

I wonder if it is something that starts happening after some uptime.
I'll try rebooting again. 

-- Fernando


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