Need some assistance understanding my Latency Test result

Sray69 wrote:

So I ran latency-histogram --nobase again to see if I get that message. My message says "Note: Using POSIX non-realtime".

Good catch! So what do I need to do to install a realtime kernel? Will this mess up the Windows OS that is loaded on it? I don't want to mess that up as that is my wife's remote computer for work.

According to the 'uname -a' output you showed earlier, you are already running a realtime kernel. The question is, why isn't latency-histogram/latency-test picking that up?

How are you running linuxcnc: Are you running a live CD/USB? If so, which image? Or did you install it to the disk? If so, how?

(The things tommylight wrote was assuming you were actually running a functioning realtime system already. Since that's not the case, no need to switch out RAM sticks and such.)

I was running LinuxCNC in Live mode from USB.

No the computer I have been working on, still does not show POSIX realtime.

However, as mentioned in my last post I have a different computer that I can repurpose for the LinuxCNC if I have to that DOES say "Using POSIX realtime" using the same USB Live. You can see the test results of that computer in my previous post. If those numbers look good then at least I know I have a computer that will work for LinuxCNC.

But if we can get the test to work correctly and get the original computer to work that would be preferred because it will take a lot of work to move around/setup/repurpose my computers.

How are you running linuxcnc: Are you running a live CD/USB? If so, which image?

I am running Live USB. What is the easiest way to find out what image I am running? Can I do it from inside the Live OS or do I have to find it another way.

According to the 'uname -a' output you showed earlier, you are already running a realtime kernel. The question is, why isn't latency-histogram/latency-test picking that up?

Well and why does my other computer pick it up correctly but not this one (from the same USB Live image)?

I guess I will format the USB tonight and install the latest version and see if that changes anything.

The version I am using is one that I downloaded 9-12 months ago. Not sure if there is a newer version out since then.

In the mean time can anyone tell me how the numbers look on my other computer? Will that work as is or does it need some extra work as well?

Sray69 wrote:

According to the 'uname -a' output you showed earlier, you are already running a realtime kernel. The question is, why isn't latency-histogram/latency-test picking that up?

Well and why does my other computer pick it up correctly but not this one (from the same USB Live image)?

That is truly weird and above my paygrade I'm afraid. Yes, I think it's a good idea to download a current image and try again.

As to your other computer: 100 µs of latency is borderline okay for a Mesa system, I think (mine is just north of 80 µs). But you need to make sure it doesn't get worse even if you run the latency-histogram for a longer period of time while stressing the computer: open a few browser windows with, say, a YouTube video and some heavy news site, start a few glxgear windows (use the button in the histogram window), and then switch between the windows a bit and see what happens with the latency.

Thanks for the suggestions. I will work on it.

I downloaded the latest version from linuxcnc.org/downloads/.

LinuxCNC 2.8.2 Debian 10 Buster PREEMPT-RT ISO

I ran the Live from USB. I then ran latency-histogram and it says "Note: Using POSIX non-realtime"

I did notice that on this computer I am getting this type of message when the histogram is running:

"msg=can't use non-numeric floating-point value as operand of "*" (variance=-2116125128)"

Where on my other computer that runs in realtime mode does not show this message. Could this be part of the reason it is not running in realtime mode?