Lowlatency kernel testing (Re: A feature for -lowlatency kernel?)

[David Henningsson]

On 2011-03-25 05:21, ailo wrote:
> I've been doing some testing on previous kernels together with a few
> people, and the sum of my experience is, just use jack with a program
> you like, try using the lowest latency you can.

Hi ailo,

I see you're the only one that has updated the wiki with info saying 
that lowlatency kernel actually gives you lower latency than the generic 
kernel.

I'm a little curious as of what is causing this. Could you please try 
the following:
- Start the latest generic kernel
- Start your audio programs (jack etc) and verify that the latency is 
still not ok/optimal. Set your latency settings to the latency that you 
are able to achieve successfully with the lowlatency kernel, but gives 
you xruns in the generic kernel.
- Run the following commands:
sudo -s
cd /sys/kernel/debug/tracing
echo 0 > tracing_enabled
echo wakeup_rt > current_tracer
echo 1 > tracing_enabled
- While in that root shell, wait for an xrun, then attach the output of 
the "trace" file here. For the trace file to be of the most use, it 
should contain a latency value of ms (as in milliseconds rather than 
microseconds), and the task should be "jackd".

You can then
echo nop > current_tracer
...to disable the tracer again, as it might take some additional CPU.

Thanks!

-- 
David Henningsson, Canonical Ltd.
http://launchpad.net/~diwic