Bad jitter on Debian Wheezy, but was OK on Ubuntu 10.04

So I've been running LinuxCNC 2.5.0 on Ubuntu 10.04 for many years until last week when the hard drive on the PC failed. I replaced the HDD and proceeded to install the current version of LinuxCNC 2.7 on Debian Wheezy from the live CD. The install went fine without any issues. Running the latency test I got a shock with Base period jitter numbers of about 3,000,000 ns and that was with only the latency test running.

This is the same computer that was running LinuxCNC 2.5 on Ubuntu, just with a new HDD. So I went to the previous version archive and downloaded 2.5.0 on Ubuntu, installed that on the computer, leaving the wheezy version intact. Again, install went fine and I started the latency test. With 5 windows of GLX gears open, and then opening multiple programs, the max base period jitter was about 17,000 ns. Not great but not bad.

So my question is why is Wheezy so bad when Ubuntu is good and is there anything I can do about it.

Thanks,

John B.

Which kernel are you using in the Wheezy install?

(uname -a will tell you)

I can't see how it could be the wrong one, but sometimes the installer will "update" to the wrong kernel during installattion. So, what latency do you get if you boot in Live-CD mode?

I'll have to check those things out. I'll report back once I find out. I'm busy for work today, so might not get to it til tomorrow.

I had to go out of town for work, but was able to check it out today. The uname -a got the following:

Linux LinuxCNC1 3.4.9-rtai-686-pae #1 SMP PREEMPT Debian 3.4.55-4linuxcnc i686 GNU/Linux

I must admit that I had not tested the latency using the liveCD, assuming it would be OK since the PC was already running a linux version before. I. didn't have time to try the live CD just now but will give it a go tonight and report back.

Thanks

That looks like the right kernel, so I am not sure what the problem is.

Were you previously running the SMI patch by any chance?