Q - nVidia 8400GS Video Card + nouveau

Hi !

I'm going to install LinuxCNC (for 3-axis CNC milling cutter) on DELL Optiplex GX620 (Pentium D930 3GHz dual-core CPU, 2GB RAM, GMA950 video), which still have parallel port, is very compact and quiet.

Video performance seem to be a big issue with these kind of PCs, so I'm going to add PCI-E low-profile nVidia GeForce 8400GS video card with nouveau open source video driver.
Full size PCI-E video cards can't be installed on this PC, only low profile.

Any suggestion(s) regarding possible problems and performance issues is very welcome.
Thanks in advance !

I have installed 8400GS, this DELL requires low-profile PCI-E cards, so choice is very small.
And now I have problem with nouveau - screen is flickering (once in several seconds).
This is nouveau problem for sure, with Win everything works fine.

Anyone have any clue how o solve this?
What is situation now with newest nVidia proprietary drivers - do they still cause latency problems?

Normally linuxcnc does not require great video performance
The onboard GMA950 video may be perfectly adequate

I have fixed flicker issue with nouveau:
added boot parameter to grub2 - drm_kms_helper.poll=0

However, latency parameters are not so good (on Dell Optiplex 760, Intel Dual CPU E2200 @ 2.2GHz, 2GB RAM, SpeedStep disabled, low power mode disabled).

nouveau (nVidia 8400 GS PCI-E)
servo thread 1ms / max jitter 45404 ns
base thread 25ms / max jitter 18068 ns

Intel GMA
servo thread 1ms / max jitter 46187 ns
base thread 25ms / max jitter 18660 ns

nouveau performance is really disappointing.
I have latest installation of LinuxCNC /Debian Wheezy DVD from this site.

Anyone have any idea what could be done next to improve real-time performance?

What is max safe pulse rate for this jitter value?

This site and the wikis etc are littered with warnings to avoid nvidia video cards.
That warning goes double, for trying to use them with proprietary drivers.
If you think your latency is bad now, install the nvidia-glx package

I have installed 8400GS, this DELL requires low-profile PCI-E cards, so choice is very small.

There are lots of low profile PCI-e video cards about, New Egg alone, lists 309 different ones.

I personally have had success with older Matrox cards, with just enough RAM to take the load off the processor.
This for instance, cheap enough to put in the spares box if it does not work or just put back on Ebay.
www.ebay.co.uk/itm/Matrox-P650-PCI-E-Low...b:g:JJQAAOSwjVVVyxKg

There are no guarantees and a lot is trial and error, so no point spending a lot on components.
The computer / video card / kernel combination has a lot of variables

This is nouveau problem for sure, with Win everything works fine.

nouveau is not really the culprit here, it works perfectly well with other nvidia cards.
Some nvidia cards are just even crappier than others, they all work well with windows, that is what they were made for.

My advice, don't get hung up on either the computer or video card, if you can't get decent latency, try another one.

regards