[LAU] Ubuntu-Studio 13.04 Nvidia drivers?

[Gene Heskett]

On Thursday 14 February 2013 13:35:26 Ralf Mardorf did opine:

> On Thu, 2013-02-14 at 12:06 -0500, Gene Heskett wrote:
> > 5 microsecond base thread jitter in its timing
> 
> I agree that the nvidia driver could cause issues, but 5 ms jitter? This
> perhaps is an issue for the RTAI, but I guess not for the audio RT
> kernels.
> 
Possibly not.  What I am pointing out is that unlike all the fussing about 
it, xruns and all, and invoking all sorts of black magic speels to control 
it, working virtually blind, on LAU/LAD, we were forced to write test 
utilities that quantified the results in an easy to understand format.  The 
net result being that we have a pretty good idea of the causes of the 
failures when the figures do blow up.

Certain motherboards are pure junk, and a few are truly outstanding given 
their relatively meager specs on the box they ship in.  The intel Atom dual 
core boards being a case in point.  The now almost out of the pipeline 
D525MW board, with a gig of ram and onboard intel video being an excellent 
example, turning in results consistently under 7 microseconds for a 
base_thread jitter when running the base IO thread at a 25 microsecond 
repeat rate.  The parent servo_thread, running every millisecond, has 
similar performance on this board.  Testwise while carving metal, I have 
run the servo_thread at 2 kilohertz with even better results, and I intend 
to raise that a kilohertz at a time until I run out of cpu because it seems 
to reduce the detected noise in a quadrature encoded spindle speed control 
as it goes up, effectively reducing the quantization errors in such a 
software only servo control.

This motherboard, an ASUS M2N_SLI Deluxe is relatively poor despite a quad 
core phenom running at 2.1 ghz with 4G of dram.

It is currently reporting the 1ms servo thread as having 15 microseconds of 
timing jitter, and nearly 45 microseconds of jitter for a 25 microsecond IO 
thread, and the machine is quite obviously 'pegged out'.

This base thread is probably not of interest to you audio people, but many 
motherboards will have far worse servo_thread timing dependabilities simply 
because the context switch takes too much time.  This is of course on an 
RTAI patched kernel, but we are about to move to the xenomi patchset, as 
its easier to do, is all user-space, and actually working at least as well 
as the RTAI patches.


Cheers, Gene
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