[PlanetCCRMA] rt kernel problems

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Sat Apr 6 13:02:08 PDT 2013

On 04/06/2013 12:01 PM, Bengt Månsson wrote:
> Hi folks,
> Again I have to call out for some advice.
> Here is what I've done:
> - Installed fresh from f18 xfce live dvd (simple partitioning with ext4)
> - Installed repos for ccrma and rpmfusion
> - updated everything except kernel (which is now 3.6.10)
> (when I tried that in one go it didn't work at all. I started fresh
> again and updated in pieces; first everything except kernel and xorg,
> then xorg).
> - removed pulsaudio

(I have not found a need to do that...)

> - added a /etc/modprobe.d/local.conf to fix the ordering of sound devices

(It is usually best to refer to the card by name instead of number and 
then the ordering does not matter - ie: use hw:NAME instead of hw:0, you 
can find the name between [] in the output of "cat /proc/asound/cards").

> - used realTimeConfigQuickScan and follow advice
> - run alsamixer to set the volumes
> - otherwise I think I kept everything default
> With this system, I can start (in order) qjackctl, jackd, qsynth and
> rosegarden.
> I can play some simple stored music. With a processor load of 5%
> (according to qjackctl) I can get a latency around 10 ms without
> problems with xrun (just).

Did you try starting the kernel with the "threadirqs" boot option? And 
running rtirq with that? It is supposed to give you better latency 
performance (that option was part of the rt patch and has since migrated 
to the mainline kernel).

What soundcard do you have?

> Not impressed. I would like to run more stuff with less latency, so I
> try to install the rt kernel (3.8.4) and rtirq.
> This configuration starts, but it's completely useless. I start qjackctl
> and jackd and it looks ok. I start qsynth and try to start rosegarden.
> The latter never starts and the machine start to behave very strange in
> many ways. Windows can be moved but the app inside is not responding.
> Windows turning white. When i try commands in the terminal some can work
> but other say "Input/output error" or "read-only file system". Only way
> to restart is power-off the hard way.

Ah, that all points to a really really bad problem, most likely you are 
managing to trigger some internal kernel bug. Do you see anything at 
that point in the output of "dmesg" or in /var/log/messages? Something 
like a BUG or OOPS followed by a dump of the internal state? If that is 
the case we should report that to the rt kernel developers...

> I have started again with the stock 3.6.10 kernel and the machine is
> working again, but without the performance I would like to see.

You could also try to update the non-rt kernel from Fedora, I think the 
current one is up to 3.8.x as well. I don't use it so I don't know if 
that will improve performance...

-- Fernando

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