[Fedora-music-list] Low Latency vs. Real Time Kernel

[Brendan Jones]

On 02/14/2012 08:31 PM, Brian Monroe wrote:
> I've been spending a lot of time on the #opensourcemusicians channel
> talking to Ubuntu Studio users about their kernel and latency times
> they're getting. Seems like most of them are using g a stock kernel with
> the preemptive option enabled and they are getting great latency results
> (2ms)while utilizing the @audio group on their user. I ended up
> compiling my own low latency kernel and I haven't had any issues with it
> yet. If this is what we are missing for the spin I'd be happy to
> maintain packaging for the kernel.  I know ccrma has been behind a few
> kernel releases.

Latency times are really relative things based on many factors. Have you 
been getting better latency times than ta

Currently 3.2.2-1.rt10.1 is in CCRMA testing (which is only one behind 
upstream which I believe Fernando has already started working on)

The patches are taken from here: 
http://www.kernel.org/pub/linux/kernel/projects/rt/

>
> I saw the instructions for adding the real time patch for a tick less
> kernel and from what I can tell it wouldn't be hard to get that rolling
> as well.
>
> I'm not entirely sure what ccrma does differently with their kernels
> compared to other Linux users, and I'm still a bit of a noob so I could
> be off base with this, but I would reason that we should be able to just
> utilize the same settings to archive similar performance enhancements.

That question might be better directed towards CCRMA.

I haven't got that far yet but I would imagine that any kernel shipped 
with a Fedora endorsed spin would have to be generated by the kernel 
team (ie, from the Fedora build system). Having said that, latency times 
achieved using the stock kernels w/threadirqs and our standard jack 
limits.conf are more than sufficient for most users.



> I thought I read that ccrma uses a unique scheduler, but if we could get
> a 2ms latency time without it, the point may be moot.
>

Brendan