[LAU] linux-rt & presonus 1818VSL

[Fero Kiraly]

I say hallo for Harry ! ;)

F:  I have some troubles - read xruns - with this setup:
H:  There's a lot more to removing Xruns from a system than just the kernel
and JACK settings (although they are very important :)
F: actually I know  realTimeConfigQuickScan, so my output looks:

*[paum at bookes ~]$ realTimeConfigQuickScan *
*== GUI-enabled checks ==*
*Checking if you are root... no - good*
*Checking filesystem 'noatime' parameter... 3.6.11 kernel - good*
*(relatime is default since 2.6.30)*
*Checking CPU Governors... CPU 0: 'performance' CPU 1: 'performance' CPU 2:
'performance' CPU 3: 'performance'  - good*
*Checking swappiness... 10 - good*
*Checking for resource-intensive background processes... none found - good*
*Checking checking sysctl inotify max_user_watches... >= 524288 - good*
*Checking access to the high precision event timer... readable - good*
*Checking access to the real-time clock... readable - good*
*Checking whether you're in the 'audio' group... yes - good*
*Checking for multiple 'audio' groups... no - good*
*Checking the ability to prioritize processes with chrt... yes - good*
*Checking kernel support for high resolution timers... found - good*
*Kernel with Real-Time Preemption... not found - not good*
*Kernel without real-time capabilities found*
*For more information, see
http://wiki.linuxmusicians.com/doku.php?id=system_configuration#installing_a_real-time_kernel
*
*Checking if kernel system timer is set to 1000 hz... found - good*
*Checking kernel support for tickless timer... found - good*
*== Other checks ==*
*Checking filesystem types... ok.*
*ok.*
*** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.*
*   Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.*
*[paum at bookes ~]$ *


and I dont understand two things:

*Kernel with Real-Time Preemption... not found - not good*
*Kernel without real-time capabilities found*
*BUT*
*[paum at bookes ~]$ uname -a*
*Linux bookes 3.6.11-rt33-1-rt #1 SMP PREEMPT RT Sun Apr 28 12:18:40 CEST
2013 x86_64 GNU/Linux*
*[paum at bookes ~]$ *

and the second, how to:
 ** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
   Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.
??

H: Known things that need to be done:
       -Interrupt requests of your hardware must be prioritized (rtirq
script helps here)
F: my system says:
      rtirq.service               loaded active exited    Realtime IRQ
thread system tuning

H:      -Interrupt thread handlers (on RT kernel) must be prioritized
F:       how to ?


H:      -Thread priorities must be checked for JACK itself
F:      How to ?



H:  Some other things to look into are:
       -CPU scaling (causes Xruns here, although others say it works fine)

       -WiFi (must be disabled here: "iwconfig wlan0 txpower off", not just
disconnected)
       -Graphics chip drivers (I'm using a standard xf86-video driver for
my ATI HD2400XT)

F:  CPU scaling seems good:
     *Checking CPU Governors... CPU 0: 'performance' CPU 1: 'performance'
CPU 2: 'performance' CPU 3: 'performance'  - good*

     WiFi - thats pity, because I often use my phone as controller
(TouchOSC)
     Graphics - Nvidia - I am using noveau driver

H:  That's a good start anyway: If I find some time, I'll write a quick
post on tuning an Arch system for maximum low-lat RT performance.
F:  appreciated ;)

F: My aim is to get as low latency as possible.
H :Please specify... How low is low :D I've achieved 0.3ms at 96kHz,
running a CPU stress test on each core without Xruns, so I'm pretty happy
with that... since the hardware (Echo Indigo DJ PCMCIA) can't handle any
lower!

F: oh, great !. it could be an ideal for me. I use various acoustic
instruments for live playing, so yes I am talking about less than 4ms


F: but none of them was without xruns when running:
        pd - plugins - ardour

H:  PD is a bit of a xrun hog on my machine here: not bashing PD, I
probably don't have it set up with ideally. But perhaps try running eg
Ardour on its own for testing purposes? Or another simple app which isn't
as dependent on the "patch" that's loaded..?

HTH, -Harry
fero
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