7i80 and 7i77

what does uname -a print?

PCW wrote:

what does uname -a print?

Linux cnc 3.2.0-4-rt-686-pae #1 SMP PREEMPT RT Debian 3.2.68-1+deb7u3 i686 GNU/Linux

Yes, but also when I now boot with the RTAI kernel its the same bad latency as if I boot with RT_PREEMPT so the installation of RT_PREEMPT seem to have made the other worse too.
So it would be interesting to know what the installation of RT did to make the RTAI be just as bad.

Its not only the price but more the size and how smooth this little box fit right back on a lcd screen.

I doubt that installing the Preemt-RT kernel can affect anything when running the RTAI kernel
its more likely something else global that you changed (grub settings BIOS settings etc)

At this point to make sure, I would boot from the live wheezy image,
and run the latency test for a few hours while running glxgears, videos etc.

If you cannot get the latency < 75 or so uSec with the wheezy RTAI image
it really looks like that motherboard is not usable for linuxcnc

Nope, yesterday I reinstalled everything (formated the drive) and I only did these steps after updating to linuxcnc 2.7 and tried the latency after every step.

sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get install linux-image-rt-686-pae.

Here it was still ok

sudo apt-key adv --keyserver hkp://keys.gnupg.net --recv-key 8f374fef
Added new source deb linuxcnc.org/ jessie base 2.7-uspace
sudo apt-get update
sudo apt-get install linuxcnc-uspace.

After this it was as bad as I stated before and it doesnt matter which kernel I boot.

Strange, maybe you lost some grub settings with the new kernel
?

When you say the stock install was OK, what was the latency after an hour or so of videos?

PCW wrote:

Strange, maybe you lost some grub settings with the new kernel
?

When you say the stock install was OK, what was the latency after an hour or so of videos?

Reinstalled the stock install again to try it from there and after a Grub tweak (isolcpus=1 acpi_irq_nobalance noirqbalance)
I got a maximum of 24000ns after youtubing an hour, mostly about 10000ns, before that I got 200000ns spikes.
I also tried this with the RT PREEMT with no succes.

So it seem the computer is fit for LinuxCNC with the stock install and this is even with default settings in BIOS.

What could it be that messes it up??

Are there any other kernels or some other workaround I could try?

another PC?

You could try an up-to-date Preempt-RT kernel (4.1.5 is the latest I think)

Here's a script that works on Ubuntu 14.04, might work on Wheezy

cd ~
sudo apt-get update
sudo apt-get install build-essential bin86 kernel-package libqt4-dev libncurses5
-dev pkg-config
mkdir rtlinux
cd rtlinux
wget ftp://ftp.kernel.org/pub/linux/kernel/v4.x/linux-4.1.5.tar.xz
wget www.kernel.org/pub/linux/kernel/projects...h-4.1.5-rt5.patch.gz
tar -xpf linux-4.1.5.tar.xz
gunzip patch-4.1.5-rt5.patch.gz
cp patch-4.1.5-rt5.patch linux-4.1.5
cd linux-4.1.5
cat patch-4.1.5-rt5.patch | patch -p1
make xconfig
make
sudo make modules_install
sudo make install


Note that isolcpus will typically make Preempt-RT latency worse, idle=poll may help