Found it! The service is called “Diagnostic Policy Service”.
The Diagnostic Policy Service enables problem detection, troubleshooting and resolution for Windows components. If this service is stopped, diagnostics will no longer function.
If you stop it voilà! No more spikes 
Anyway, as always, do it at your own risk. I have not investigated what issues could cause disabling the service. If you don’t know how to stop a service please google it or ask chatgpt.
Enjoy lower latencies!
Thanks for the additional info! I will probably look at using Process Lasso to suspend this task when Cubase is running. There may be ways to manage the impact via priorities or affinities as well.
Thanks @itsmeuy !
Disabling ‘‘Diagnostic Policy Service’’ removes that ntoskrnl.exe DPC spike indeed!
Thank you for the deep research and post! Excellent work! This makes Windows 11 very good for music production and DPC free!
Does anyone know if this is specific to Windows diagnostics only? Or does it prevent Cubase from doing its thing or error logging if it has a crash?
I do not see “Diagnostic Policy Service enables” in Process Lasso. I see it in Services. Please let me know if or where you find it in Porcess Lasso. Thanks!
Haven’t looked at this yet but will report on my finding. It may require some scripting support, don’t know.
Thank you so much, I use standalone apps when practicing and Cubase for recording, so will turn it off and take any consequences, given it’s two weeks since the last post and nobodies come back with any issues it seems really good
I’ve made a Steinberg account just to say this:
THANK YOU SO MUCH.
I have been struggling with this exact issue for days now and I was so close to giving up on it. 600-1000us spike pretty much every 15min.
I tried creating traces with WPR but I could not isolate the problem.
Disabling “Diagnostic Policy Service” fixed it.
Again: Thank you.
Created account just to say thanks!
Have no idea what cubase is, or anything else related to this forum, but I have been trying to diagnose my dpc latency spikes that I only knew existed due to noticing audio pops while using Microsoft Flight Simulator. Tried every fix I could find online, but after stopping the “Diagnostic Policy Service” and setting it to “manual” instead of automatic start has completely stopped my ntoskrnl.exe related dpc spikes.
The nvidia kernel is still causing spikes to around 700-800 uS occasionally, but this is still much better than the spikes I had before.
So thanks very much. Hours of research, nothing worked except this simple fix.
You have landed in the place where people make music.
I really don’t like the idea of disabling “Diagnostic Policy Service”. This is an important service for windows in general. Probably I could try to do that in my AHK script temporarily which starts Cubase acrually.
I tried it already manually bit the effect was an (massively) decrrased DPC latency for ntoskrnl but a recognizable big increase Value for interrupt to process latency. Do, this “fix” comes for a price,
But I am still pretty sure tjat these 15-minutes spikee come from a background service which has this feature hard coded anywhere. I explored literally all background processes in tasl manager but nothing changed. Even different GPUs (Intel or Grorce) did not make any difference.
