[LAU] Too many xruns

[Kevin Cosgrove]

On 7 September 2012 at 10:17, Joakim Hernberg <jbh at alchemy.lu> wrote:

> On Thu, 06 Sep 2012 10:02:11 -0700
> Kevin Cosgrove <kevinc at cosgroves.us> wrote:
> 
> > 
> > On 6 September 2012 at 8:43, Kevin Cosgrove <kevinc at cosgroves.us>
> > wrote:
> > 
> > > > >> cat /proc/interrupts
> > > > >
> > > > > Xrunning system says:
> > > > >
> > > > >        CPU0   CPU1   CPU2   CPU3   CPU4   CPU5   CPU6   CPU7
> > > > > 16:    56322  0      0      0      0      0      0      0   
> > > > > IO-APIC-fasteoi   ahci, ehci_hcd:usb1, firewire_ohci,
> > > > > snd_ice1712, nvidia
> > > > 
> > > > That would give me xruns too.
> > > 
> > > OK.  I see it now.  I've never had to fight the interrupt problem
> > > before.
> > > 
> > > > (if you can) See if you can set IRQ in the bios for that slot
> > > > to something else if there is only one.
> > > 
> > > I'll look at the manual for my MB and see what I can do.
> > 
> > I did a search for "irq" on this website
> > 
> > http://www.manualowl.com/m/Asus/P8Z68-DELUXE%2FGEN3/Manual/263040?page=91
> > 
> > and found a page (2-14) that lists the (non-alterable???) IRQ 
> > assignments for my motherboard.  The good news is that one of
> > the legacy PCI slots has less stuff on the IRQ.  The bad news
> > is that one of the PCI slots has lots of stuff on that IRQ.
> > 
> > Looking at IRQ 16 above, my nVidia shows up.  It's PCiE x16,
> > and my motherboard seems to have 3 of those slots, with one slot
> > being on a different IRQ.  I suspect moving the video card might
> > help, right?
> > 
> > Basically, my strategy would be to disable drivers I don't use.
> > For instance, I don't have any firewire gear.  Next, I'd move
> > anything I could to a slot using a different IRQ than the one
> > I want to reserve for the Delta 1010.  Seem like a good plan?
> 
> FWIW, I have a similar system with an Asus P8Z68-V PRO GEN3 + Intel
> i7-2600k CPU,

That is VERY similar, and gives me hope.

> I have an rme multiface PCI card in a slot that gives it
> IRQ 18 all to itself.  The only irq priority manipulation I do is to
> run chrt -f -p 98 `pgrep irq/18-snd_hdsp` from /etc/rc.local.
> 
> I also have the system running with the default ondemand governor.

Nice.  Again, the IRQ isolation theme.

> I don't use an external NVIDIA card as the built in HD3000 GPU works
> a treat for low latency audio even with a full KDE install with
> compositing kwin.  If I did use a NVIDIA card I would most likely use
> the nouveau driver that lately has become very good for low latency
> audio.

The nouveau driver didn't do so well with my dual monitors.  Ardour 
is _great_ with the mixer window on one monitor and the editor window 
on the other.

> Kernel is 3.4.9-rt17.  Running cyclictest -m -Sp99 -i100 -d0 shows me
> kernel scheduling latencies of well under 0.1ms no matter how hard i
> push the system, and that is with the ondemand governor...

Nice.

> All in all very pleased with this system, and I think you will be
> too if you move the soundcard to another slot,  having less stuff on it.
> 
> Another tip, if you have to use a slot that shares IRQs, then you have
> to raise the priority of all the soft interrupt threads that share
> the IRQ with the soundcard, otherwise you will get a lot of xruns.

More with the IRQ isolation and prioritization theme.  I haven't had 
time to play with that.  But, it's next on my list after I get done 
with a recording project using the other system.

Thanks!!

--
Kevin