Installing LinuxCNC 2.9 or Master on Linux Mint 21

  Soo. After beeing forced  to change lcd controller, some extra space was freed in my panel pc controller, so buttuns and status leds moved to proper position. And goodbay ugly add on box..  

@tommylight thanks! I've got it running on an Optiplex 7040, but had some latency issues.
I'm a bit surprised that all these low latency kernel debs have their clock set at 250 Hz instead of 1000 Hz, After compiling one with the clock set at 1000 Hz It seems to do a bit better, latency was first 90000ns, now 58000ns. Still not great, but acceptable with mesa I think. I might gonna look into unlocking bios options, I've done that before with a laptop which had great results.

royka wrote:

@tommylight thanks! I've got it running on an Optiplex 7040, but had some latency issues.
I'm a bit surprised that all these low latency kernel debs have their clock set at 250 Hz instead of 1000 Hz, After compiling one with the clock set at 1000 Hz It seems to do a bit better, latency was first 90000ns, now 58000ns. Still not great, but acceptable with mesa I think. I might gonna look into unlocking bios options, I've done that before with a laptop which had great results.

Can you share that kernel to test it?

Ismacr63 wrote:

Can you share that kernel to test it?
 

Sure, I did however disable some AMD graphics drivers, so if you need these I could eventually compile a new one. It's actually pretty easy to do it yourself if you want to. As reference I used this page:  github.com/Jiseoup/preempt-rt/blob/main/README.md

With this kernel somehow I had to manually edit grub
uploadify.net/6bdcf22b29f8effc/Linux-ker....5-rt14-amd64.tar.gz

Here the debs of kernel 6.2 rc3 with rt patch and CONFIG_HZ_1000=y
uploadify.net/e9ff67b98f170eb3/kernel-6.2rc3.tar.gz

Update: After adding a RAM module to let it operate dual channel, I've been testing it for a few hours with youtube and 15 tabs open, installing various stuff, a max jitter of 40 us. I'm satisfied. While with another pc there was a huge improvement after removing a RAM module.
So you could try with a second ram module, that seems to work best if you've 2 of the same, however at the moment I'm testing with 2 different brands which work well. 

Since the rt patched kernels from Debian has PREEMPT_DYNAMIC=y in its config, shouldn't we use preempt=full as bootarg parameter?
I'm testing it now and got a max jitter of 30us instead of 40us, could be a coincident but I could not get it higher yet. I'm curious if others would see an improvement too.

royka wrote:

Since the rt patched kernels from Debian has PREEMPT_DYNAMIC=y in its config, shouldn't we use preempt=full as bootarg parameter?
I'm testing it now and got a max jitter of 30us instead of 40us, could be a coincident but I could not get it higher yet. I'm curious if others would see an improvement too.

I have tried your latest kernel 6.2 rc3 and I have managed to lower 15us.

How can I test PREEMPT_DYNAMIC=y?

"PREEMPT_DYNAMIC=y" is an option you could set before you compile which is also set at that kernel, From what I understand it means that you then need to add the boot parameter preempt=full to get the lowest latency, but I could not find a lot info about that.

The easy way to test without a permanent change is when you're in grub @ boot, press "E". Then you could add preempt=full in probably the second last line, in front of "quiet splash". Then press CTRL + X to boot. After a reboot that setting is gone.

if you type uname -v is PREEMPT_DYNAMIC still reported after you install the linux-image-rt and reboot?

 I had a feeling it showed preempt_rt on a reboot.

It showed preempt_rt indeed.
I couldn't find anywhere that it should show preempt_dynamic otherwise, but it seems logically that it should. I was searching about that config option and found that boot parameter, tried that and it showed a latency of 10us less than before with whatever I tried.
But perhaps the higher latency before that boot parameter was an incident.