Re: [LAU] Hardware latency of firewire controller - Linux-audio-user

18 Apr 2008

Ismael Valladolid Torres wrote:
...
  Thanks a lot for the kind support!

 On Thu, Apr 17, 2008 at 11:52 AM, Pieter Palmers &lt;pieterp(a)joow.be&gt; wrote:
   IRQ sharing is not a good thing, so avoid it as
you can. Again the "32" is
 not easy to interpret correctly. Read the following page to understand it:
 http://www.reric.net/linux/pci_latency.html  
 Being the only device reporting a PCI latency value does mean that the
 firewire controller is the only one doing bus mastering in that system
 setup? 
no, because most of your devices are PCI-express, and the pci-express 
bus doesn't have the latency concept. However from a "programming" point 
of view pci-express is backwards compatible to PCI, hence they report a 
value (of 0), although it doesn't mean anything.

...

   Can you please provide the following
information:
  1) the output of the attached script (python listirqinfo.py)
  2) the full output of lspci -v
  3) the jack command line used (if you use qjackctl you can run the
 following command in a terminal to get the last command line used: "cat
 ~/.jackdrc"  
 marcel@ubuntu:~$ cat ~/.jackdrc
 /usr/bin/jackd -R -p128 -dfreebob -r44100 -p512 -n3 -D

 Check out attached files for the rest of the info. Again, thanks a lot!

There is one problem with your setup: all interrupts run RT at priority 
50. However, jack defaults to a priority of 20. This causes two 
problems: first of all the 1394 interrupts don't have higher priority 
than other interrupts, hence can be delayed too long. Second: jack has 
lower priority than all interrupts, hence can be delayed too long. The 
main problem usually is the graphic card.

Can you check whether the following helps:

1) change the IRQ priority (possibly as root):
chrt -f -p 99 `pidof "IRQ-11"`

2) run jackd with the following command line (not as root):
/usr/bin/jackd -R -P70 -p128 -dfreebob -r44100 -p512 -n3

This should improve the situation. If so, please configure Rui's rtirq 
script as described in: 
http://freebob.sourceforge.net/index.php/IRQ_Threading_and_Priorities

you might even want to set the RTIRQ_RESET_ALL option to 1 in the config 
file described on that page.

Greets,

Pieter