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?

Short answer = use the built in graphics
Long answer = most AMD cards work with open source drivers that come with Linux, i have several RX580/8GB and had RX6700XT, RX6800XT, RX6900XT and all worked fine, but none of them work with proprietary AMD drivers as the Real Time kernel does not like the proprietary drivers.
I did say "most", some older ones will not work no matter what.
And in general NVIDIA is worse, with open source and proprietary drivers.
Very old Matrox cards were good, but those were AGP, not PCI-E.

zmrdko wrote:

Is there any hack how to tackle with radeons?

GRUB_CMDLINE_LINUX_DEFAULT="quiet isolcpus=4,5 radeon.dpm=0"
GRUB_CMDLINE_LINUX_DEFAULT="quiet isolcpus=4,5 amdgpu.dpm=0"

Not sure which works...
 

well, this is so much better:
 
 

That looks very good, even for software stepping with parallel port.
Move on to making chips!