[LAD] PCI MIDI jitter - comparison Ubuntu (bad) and Suse (might be ok)

[Ralf Mardorf]

On Sun, 2010-07-11 at 17:21 +0200, Arnout Engelen wrote:
> On Sun, Jul 11, 2010 at 04:53:14PM +0200, Ralf Mardorf wrote:
> > today I compared a default Ubuntu Studio with and without the
> > proprietary NVIDIA driver. 
> 
> OK, so the proprietary driver seems to yield better 'worst latency' values 
> compared to nouveau. That's kind of odd, anything X-related would have a much
> lower priority than the MIDI threads.
> 
> > Note that for Ubuntu Studio 2 tests failed because of time out errors
> 
> What exactly timed out?

There was a time out message by the alsa-midi-latency-test. It started
and than it asked, if there still is a connection, while there still was
a connection.

> 
> > even the tests that were passed with success are significantly less good, 
> > than the tests with openSUSE, were I set up audio myself.
> > 
> > What might be the difference between Ubuntu and Suse?
>  
> > ------------------------------------------------------------------------
> > Ubuntu Studio 10.04 amd64
> > 2 x Terratec EWX 24/96 (2 single cards, but 1 virtual card)
> > Frequency scaling ?
> > ------------------------------------------------------------------------
> > spinymouse at ubuntu:~$ uname -a
> > Linux ubuntu 2.6.32-23-preempt #37-Ubuntu SMP PREEMPT Fri Jun 11
> > 10:19:07 UTC 2010 x86_64 GNU/Linux
> > spinymouse at ubuntu:~$ envy24control
> > 0xcf00, irq 20, Master Clock int 44100
>  
> > ------------------------------------------------------------------------
> > openSUSE 11.2 amd64
> > 2 x Terratec EWX 24/96 (2 single cards, but 1 virtual card)
> > Frequency scaling performance
> > ------------------------------------------------------------------------
> > spinymouse11.2 at suse11-2:~> uname -a
> > Linux suse11-2 2.6.31.6-rt19 #1 SMP PREEMPT RT Wed Nov 18 16:59:26 CET
> > 2009 x86_64 x86_64 x86_64 GNU/Linux
> 
> 2 differences jump out: 
> 
> - the frequency scaling is set to 'performance' on your suse install and to 
>   '?' on your ubuntu install.

Yes, I assume that an audio distro won't start with ondemand by default,
I'll run hwinfo to see the scaling next time. For Ubuntu Studio there
are a lot of issues that are nwe to me, no xorg.conf, no menu.lst etc..

> - The kernel options for your suse install has the options 'SMP PREEMPT RT', 
>   while your ubuntu install has the options 'SMP PREEMPT'. In other words, it
>   looks like your ubuntu kernel has 'normal' preemption, but not the -rt 
>   patch.

I didn't noticed that, you're right. The Suse kernel is self build, the
Ubuntu Studio kernel is from the repositories.

> The latter looks like a good candidate for explaining the difference. Could 
> you test with the kernel from the linux-image-2.6.31-10-rt package instead of 
> the kernel from the linux-image-2.6.32-21-preempt package which you seem to be
> using now?

Thank you, a good idea, before I'll build a kernel by myself, it would
take around 50 minutes, I'll install this kernel from the repository.

To be continued.

Ralf

> 
> 
> Kind regards,
> 
> Arnout