Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)

Hi folks.

I am running linuxcnc 2.9.2 on debian bookworm (kernel 6.1.0-18-rt-amd64) on DELL Optiplex 7060  (i5 8500/32GB Ram, Radeon R5 430)
and I am getting nasty latency spikes (300 us), while alt-tabbing or basically moving windows. If I dont touch anything, latency is consistent around 0 for minutes.
Once I start resizing latency-plot window or launch firefox I get latency spikes.
Do I have issue with video driver? lspci -vv says Kernel driver: radeon, Kernel modules: radeon, amdgpu.
I tried different servo threads - from 125000 to 1000000ns.

is there a way to exactly trace, what caused the spike?

(grub config is isolcpus (tried 2,3,4,5 or 4,5 or even 5 only) idle=poll processor.max_cstate=0 intel_idle.max_cstate=0
everything is turned off in bios (there are c states explicitly)

could it be M2 ssd disk?

Please help!
Thanks

Try the rt_setup script from this post and see if it helps.

forum.linuxcnc.org/38-general-linuxcnc-q...nity?start=10#293049

Try removing the graphic card, see if that gets rid of spikes.

I am with Tommy. It sounds video card related. Remove the Radeon card and use the onboard video
as far as isolcpus go on 6 cores, I don't know what is correct, I think that script is the best option as i think it queries the system to decide which cores to isolate.

rodw wrote:

I am with Tommy. It sounds video card related. Remove the Radeon card and use the onboard video
as far as isolcpus go on 6 cores, I don't know what is correct, I think that script is the best option as i think it queries the system to decide which cores to isolate.
 

I removed Radeon card and spikes went away, even though the latency triangle is more obese now:
 

The situation is same on both Optiplexes: 7060 and 5050, since they both have radeon graphic cards. I would guess it's caused by some kind of power saving feature.
Is there any hack how to tackle with radeons?
Or should I get some older radeon? Or is there any verified gpu that works fine?