linuxaudio.org

On Thu, 14 Feb 2013 12:06:06 -0500, Gene Heskett wrote:
> On Thursday 14 February 2013 11:54:38 John Murphy did opine:

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>

> > On Wed, 13 Feb 2013 21:12:57 -0800, Len Ovens wrote:

> > > On Wed, February 13, 2013 8:59 pm, John Murphy wrote:

> > > > Well I just tried an Xubuntu 13.04 'daily' build and, similarly to

> > > > Ubuntu, I got a login prompt without X running and installed

> > > > nvidia-310-dev, which works OK. It takes ages, compared to Studio,

> > > > to boot from Grub to login though, so there's some magic under the

> > > > hood of the Studio version I think.

> > >

> > > Ubuntustudio took xubuntu as it's start at 11.10 and probably hasn't

> > > merged in any new stuff xubuntu has since then. So there may just be

> > > less stuff in Studio.

> >

> > It certainly makes for a very slick distro and one I'll probably use

> > until KDE5, if not forever!

> >

> > Tried one more time with the low-latency 3.8.0.6 kernel, but no go.

> > As soon as I rebooted after installing Generic, nvidia-310-dev was

> > up and running, which is great. Means I'll be able to compare the

> > performance of the two kernel types, which could be useful.

> >

> > Thanks.

>

> John, in my experience, you are shooting yourself about kneecap high by

> running the nvidia driver. It gets part of its performance by locking out

> the interrupts, for extended periods of time.  For an app that needs true

> real time, such as linuxcnc, a 5 microsecond base thread jitter in its

> timing, has been logged as creating latency jitters in the 200 millisecond

> range.  Even for the more forgiving servomotor stuff its not good, and its

> totally intolerable for steppers which need a steady heartbeat to move at

> more than creep speeds.

Thanks for that Gene. Really interesting. I tried searching the net

for anything which would provide more information, and about all I could

quickly find was where older Linux kernels used 'edge detection' for

interrupts as opposed to 'level detection'. I see LinuxCNC still uses

either 2.4 or 2.6 kernels, which are the ones mentioned in the article.

Maybe things have improved with all the fine work which has gone into

the kernel since then. In Linus I trust. ;)
> The nouveau driver gained some support for the 3d stuff recently, and it

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> should be checked out to see if it makes the xruns and such worse or

> better.  As a final check to see if the video is an xrun causer, try the

> vesa driver, there have been times when I was forced to use it on my

> machine tool (cnc machinery) controllers.  Poor display of course, but the

> machine worked great.

It will be easy enough to compare as the low-latency kernel can't

work as is with the Nvidia driver, so I'll be able to switch between

Generic + Nvidia and low-latency + Nouveau. I may have already used

the Vesa driver. I was limited to 640x480 at one stage. :)
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