[LAU] Ubuntu Hard real time kernel (2.6.24-21) poor performance.

[Pieter Palmers]

John Tomlinson wrote:
> After a number of years of making successful music recordings using a
> combination of rosegarden and ardour on my Ubuntu Dapper Drake system,
> and my home grown real-time kernels, I thought it was time to upgrade to
> Hardy Heron and use the proper real time kernel that the experts had
> built. What a disappointment!
> 
> I have an internal pci sound blaster live card (emu10k1 chip set) and a
> M-audio audiophile USB sound module.
> 
> On my dapper installation, which happened to have 2.6.22.1 real time
> patched kernel (the default ubuntu kernel was 2.6.15), I could get
> latencies as low as 1.5ms (32 frames/period) on the sound blaster and
> 2.7ms ( 64 frames/period) on the USB Audiophile with very few xruns; so
> few xruns that I used to wonder why people posted to mailing
> lists/forums about the problem.
> 
> With the stock Ubuntu 2.6.24-21rt kernel the sound blaster gives xruns
> every few seconds with no load (no recording and no playing back) at
> 23ms latency (512 frames/period) and the Audiophile struggles at 43ms
> ( 1024 frames/period); I am getting xruns every 10-20 seconds. Infact
> the rt kernel gives little, if any, improvement over the generic kernel.

I cannot really help you here, but I can confirm that there are quite 
some FFADO users reporting xruns on the more recent ubuntu releases 
(Hardy and Intrepid), even with RT kernels. Personally I run Gutsy and 
even with the 2.6.22-15-generic kernel it hardly ever gives me xruns.

Good to know that it might be a kernel scheduling issue, and not 
something in my code.

Greets,

Pieter