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

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16 Feb 2024 15:16 - 16 Feb 2024 15:34 #293511 by zmrdko
Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430) was created by zmrdko
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
Last edit: 16 Feb 2024 15:34 by zmrdko.

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16 Feb 2024 16:04 #293514 by mozmck
Replied by mozmck on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
Try the rt_setup script from this post and see if it helps.

forum.linuxcnc.org/38-general-linuxcnc-q...nity?start=10#293049
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16 Feb 2024 16:49 #293523 by tommylight
Replied by tommylight on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
Try removing the graphic card, see if that gets rid of spikes.
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16 Feb 2024 17:12 #293527 by rodw
Replied by rodw on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
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.

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16 Feb 2024 20:10 - 16 Feb 2024 20:10 #293541 by zmrdko
Replied by zmrdko on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)

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:
 
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Last edit: 16 Feb 2024 20:10 by zmrdko.

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16 Feb 2024 20:14 #293543 by zmrdko
Replied by zmrdko on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
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?

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16 Feb 2024 21:02 #293544 by tommylight
Replied by tommylight on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
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.

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16 Feb 2024 21:16 #293546 by Mecanix
Replied by Mecanix on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)

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...
 

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16 Feb 2024 22:54 #293549 by zmrdko
Replied by zmrdko on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
well, this is so much better:
 
 
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16 Feb 2024 23:41 #293554 by tommylight
Replied by tommylight on topic Latency spikes on Dell Optiplex 7060 (i5 8500/32GB Ram, Radeon R5 430)
That looks very good, even for software stepping with parallel port.
Move on to making chips! :)

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