[LAU] Too many xruns

[Kevin Cosgrove]

On 11 October 2012 at 9:07, Jeremy Jongepier <jeremy at autostatic.com> wrote:

> On 10/11/2012 08:33 AM, Kevin Cosgrove wrote:
> >
> >> More information on tweaking your setup:
> >> http://wiki.linuxmusicians.com/doku.php?id=system_configuration
> >
> > I've been trying to reduce my xrun troubles.  I'm down from > 10
> > xruns per second to something more like 10 xruns per minute.  Still
> > not good, but better.
> >
> > I used the realTimeConfigQuickScan.pl script to diagnose things.
> >
> > https://code.google.com/p/realtimeconfigquickscan/
> >
> > I'm down to three things reported as "not good" now.
> >
> > 1.  Checking checking sysctl inotify max_user_watches... < 524288 - not good
> >      increase max_user_watches by adding 'fs.inotify.max_user_watches = 524288'
> >      to /etc/sysctl.conf and rebooting
> >      For more information, see
> >      http://wiki.linuxmusicians.com/doku.php?id=system_configuration#sysctl.conf
> >
> >      Looking at the link there's a comment, "...it remains very
> >      unclear ... if adjusting this value actually does anything at
> >      all."  So, I haven't altered this.  Does anyone have
> >      experience saying that this helped them?
> >
> 
> Hello Kevin,
> 
> I've added this comment after having asked the exact same question at my 
> LAC2011 workshop. Nobody in the audience could acknowledge that changing 
> the inotify setting helped anything.

Nice to know.

> > 2.  chrt: failed to set pid 0's policy: Operation not permitted
> >      Checking the ability to prioritize processes with chrt... no - not good
> >      Could not assign a 80 rtprio value. Set up limits.conf.
> >      For more information, see
> >      http://wiki.linuxmusicians.com/doku.php?id=system_configuration#limits.conf
> >
> >      I did make the changes outlined at the above link.  I still
> >      get the above report.  I'm going to guess that I need some
> >      real-time support from the kernel to make this work.  Which
> >      brings me to
> >
> > 3.  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
> >
> >      First I looked at this link:
> >      http://wiki.linuxmusicians.com/doku.php?id=system_configuration#the_kernel
> >      Specifically, I looked at the threadirqs kernel option.
> >
> > grep -e CONFIG_IRQ_FORCED_THREADING=y -e CONFIG_PREEMPT=y /boot/config-`uname -r`
> >      produces "CONFIG_IRQ_FORCED_THREADING=y" and I think that's good.
> >
> 
> No it's not, unless it also outputs CONFIG_PREEMPT=y. if it doesn't than 
> your kernel isn't preemtible and in that case I doubt if threadirqs or 
> even chrt works (no expert on this).

A comment at the above link says, "If [the grep command]
returns CONFIG_IRQ_FORCED_THREADING=y and CONFIG_PREEMPT=y
then your kernel is using IRQ threading and you don't have
to proceed with the following steps. If it only returns
CONFIG_IRQ_FORCED_THREADING=y you can add the threadirqs boot
option as described..."  My grep was in the 2nd case, with
only CONFIG_IRQ_FORCED_THREADING set to "y", so I proceeded
with the rest of the "threadirqs" instructions related to grub.
That didn't seem to work.

> >      I altered my /boot/grub2/grub.cfg file to include
> >      "threadirqs" on the stanza for my kernel, like so, but
> >      without all the line breaks.
> >
> >      linux   /boot/vmlinuz-3.5.5-2.fc17.x86_64
> >      root=UUID=77edf07a-a49b-48dd-82c8-2f9e5c8691b7 ro nomodeset
> >      rd.md=0 rd.lvm=0 rd.dm=0 SYSFONT=True  KEYTABLE=us rd.luks=0
> >      LANG=en_US.UTF-8 rhgb quiet threadirqs nouveau.modeset=0
> >      rd.driver.blacklist=nouveau
> >
> 
> Slightly OT, but wow, that's a whole lot of kernel options ;) I only use 
> two or three.

I left all of that in there from Fedora's installation of the kernel.

> Check if your kernel is preemtible (at least, I think that might be a 
> probable cause) or install a kernel that is preemtible

# CONFIG_PREEMPT_RCU is not set
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

> (there's no real-time kernel available for FC17?).

CCRMA has kernel-rt-3.4.11-1.rt19.2.fc17.ccrma.x86_64 but it
doesn't play nicely with my nVidia card and X config.  I changed
the X config to use the nouveau driver, which got it to boot to
level 5 at least.  But the geometry is not good and that driver
ignores my 2nd display.  I found A LOT of potentially useful
information with a websearch for enabling an nVidia driver with a
CCRMA kernel.  Sorting that out is a possibility.

Thanks....

--
Kevin