[LAU] Too many xruns

[Jeremy Jongepier]

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.

> 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).

>      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.

>      "uname -r" reports "3.5.5-2.fc17.x86_64" but I don't have
>      threaded IRQs.
>
> Any ideas on how to improve my IRQs?  They are not alterable in the BIOS.
>
> Thanks....
>

Check if your kernel is preemtible (at least, I think that might be a 
probable cause) or install a kernel that is preemtible (there's no 
real-time kernel available for FC17?). But like I said, I'm no expert on 
the different preemption models so I could be completely wrong. 
Hopefully someone with more knowledge on this matter chimes in.

Best,

Jeremy

> --
> Kevin
>
>
>
>
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