Hardware latency tests, used PC's

EricKeller wrote:

I usually set an lcnc pc up with isolcpus. Unfortunately I couldn't find any interesting interrupts to change affinity for, that seems like it could lead to a big improvement in latency.
 

This is only useful if you are running a Mesa card or similar ethernet card. Then you can use affinity of the NIC IRQ to be the same as the isolated core.

That's what I tried to do, but no joy. I figure you could move userland irqs off of the isolated cpus as well, but I didn't see any good candidates.
Apic is stuck to cpu 0, and that's where my nics both are.

This page may be useful
Find your nic name with ip a (mine ie eno1)
type cat/proc/interrupts and look for the CPU that the NIC is on. In my case here CPU 8
 
Now open linuxcnc and not the core its running on. To do this, open linuxcnc and repeat the test you should see a new thread callrd rtappoapp or similar, Note the CPU the same way, (it should be on an isolated core)
Then use afinity commands to move the  NIC to that CPU

 

It's been a while since I tried to change interrupt affinity, but I don't think I can do anything useful in the case of this particular computer. I forget where I got the idea, do you know of anyone that has improved performance by changing interrupt affinity?


Also, I didn't find anything in /proc/interrupts that starts with rtapp. Checked to see if I was running a preempt kernel, and I am.

Hey Tommy... you have posted a lot regarding computers and latency. I found this listing that dates back to 2022. I'm running Debian Bookworm 12.4, Linuxcnc using a Mesa 7i96s card. I'm currently using a Fujitsu Esprimo D757 DT Intel i5 8 GB RAM. The latency is terrible. I started running a graphic intensive vcarve and received latency errors. I think I'd be better off purchasing another computer. Would the Dell 980 you mentioned be a good option or is there a better choice?

I had those Fujitsu, 4 versions of them, all worked perfectly latency wise, so
-disable hyperthreading
-disable TPM
-disable virtualization
-disable power savings, all
-disable turbo
Not sure what else, it was a few years back, but try those first.
Fujitsu uses very good thermal compound so if the processor has not been removed, it should be OK.