HP dc5100 Latency Spikes

Hi guys,

Though I am not new to cnc, I am trying to take the leap from Mach3. Prior to installing the live disk with Linuxcnc 2.6 and Debian, I had no prior experience with Linux whatsoever and am finding the learning curve pretty steep.

The thing is that I have Debian and Linuxcnc 2.6 installed in an HP dc5100 pentium 4 dual core pc, with 3.2Ghz processor and 2Gb ram. I have seen published specs saying the onboard graphics card is an Nvidia, though I am not 100% sure whether that is the case. I have disabled hyperthreading in the BIOS and have turned off all power management options as far as I could.

I have also done the isolcpus=1 thing.

When I run the latency test with six websites open, ten instances of glxgears and moving windows about, both the servo thread and the base thread show a jitter of about 6,000 - 8,000 ns. After a while, and without doing anything, the base thread jumps to 21,000 - 23,000 ns (though the servo thread stays at about 8,000 ns). If I open a Youtube video, both the base thread and servo thread jump to 50,000 - 51,000 ns.

That leads me to suspect the graphics card, but the jump in the base thread from 8k to 23k, I am not sure about. Any ideas?

By the way, as I read here the Matrox graphics cards might solve some latency issues, I bought a Matrox G550 on eBay, soon to arrive. When it does, do I just drop it in a pci slot, plug my montor to it and off I go, or do I have to run any scripts for the system to disconnect from the on board graphics and take the G550 into account instead?

Thanks in advance guys,

Fito

Hi Andy,

Thanks for your reply. No, there doesn't seem to be any periodicity to it at all - or predictability. I just had my first spike after about 16 minutes (went from 11k to 33k), when logging in to reply to you.

I intend running a highly modified BF20 milling machine on steppers and in real life this machine will live in my garage next to the mill and won't be connected to the internet, so I am not sure whether I should not include internet surfing, Youtube, etc. when testing latency. Maybe I should run a more "real life" test and report back. The unpredictability of these spikes still concerns me though...

What else should I try?

Update: I just ran a latency test without any websites open, just five instances of glxgears running. When I moved the latency test window about the screen quickly, the base thread jitter jumped from 7k to 20k, which seems to point to the graphics.

I later reset the test and left it alone (didn't touch anything) and the base thread jumped from 7k to 14k after about five minutes (some power management process?). The servo thread always stays put at about 7k.

I then tried to repeat the last test and the base thread went from 7k to 9k after seven minutes and from there to 17k after 8:30 minutes.

Help please!

Well, that's great news Andy, thanks.

One more thing: when the Matrox graphics card arrives, do I just slot it in, plug in the monitor and go, or is there anything else I need to do for the system to now take the new crad into account and forget about the onboard one?

Thanks again.