Ubuntu Studio Project Lead

Brian David beejunk at gmail.com
Fri Jun 11 05:57:51 BST 2010

On Wed, Jun 9, 2010 at 1:24 AM, Alessio Igor Bogani <abogani at ubuntu.com>wrote:

> Hi Brian,
> 2010/6/8 Brian David <beejunk at gmail.com>:
> [..]
> > On a final note, a long running issue for me is how often a quality rt
> > kernel is left out of the releases.  On my system, at least, the RT
> kernel
> > is the only one that gives good enough performance.  The vanilla and
> preempt
> > kernels produce far too many x-runs.  I seem to have no problems with the
> > 2.6.31 RT kernel, but it would be awfully nice to have a 32 version.
> Could you evaluate and compare those results with -lowlatency kernel
> available on https://launchpad.net/~abogani/+archive/ppa/+packages<https://launchpad.net/%7Eabogani/+archive/ppa/+packages>
> ,
> please?
> Thank you very much.
> Ciao,
> Alessio
I spent a bit of time with the kernels in your PPA, with these JACK
settings:  48khz sample rate, 512 frame, 3 buffers, 32 msec latency.  All in
all, fairly light settings.  Also, here's a quick rundown of my hardware, if
it's helpful:

MacBook, first generation
Intel core2duo 2.0 ghz processor (not capable of running 64bit)
PreSonus Firepod firewire audio interface

With the -lowlatency kernel, performance was moderate.  Running Hyrdrogen
through a few JACKRack effects for a little while didn't produce any x-runs
(except on the program start-up, which is probably to be expected.)
However, I opened some fairly complicated mixing sessions in Ardour, which
pushed the DSP to around 40%, and I started getting x-runx every minute or
so.  This is better than the vanilla kernel, but not quite good enough for
my needs.

I tried out the -realtime kernel, and it worked like a charm.  Ran a very
complicated Ardour session (upwards of 80% DSP) and had not a single x-run
after 30 minutes.

I do notice that the kernel page Scott referenced did say to only use the
-realtime kernel if the other ones do not work.  Is there something I should
know about this kernel if I plan to use it extensively?  As in, it's not
going to kill my computer or anything, right?

-Brian David
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