Initially, I thought this is related to Interrupt Moderation / Coalescing on the network interfaces, but apparently that is not related.
This does correspond to what LatencyMon (from Resplendence) reports as Interrupt to Process latency (with peaks of ~12 milliseconds).
There's no pattern to it that I could find. These bursts keeps happening 5 - 30 seconds apart, with no correlation to other CPU activity.
At the same time neither LatencyMon, nor xperf identifies any DPC or ISR from any driver as taking longer than 250 microseconds (i.e. peak, averages are much lower).
LatencyMon suggests disabling CPU throttling (which I have already done).
Not sure if it's related, but in a user mode app, if I write a simple while loop with a 1 millisecond sleep, from time to time it also wakes up after 12 milliseconds (instead of 1 or 2) - once again corresponding to the peaks shown by LatencyMon.
I've tried removing or disabling most other devices (WiFi, BlueTooth, other USB devices, VirusScan, FireWalls, etc.), but none of it seems to make a difference).
It's almost as if something is disabling interrupts for 12 milliseconds.
Any ideas on finding what might be causing this, or how to fix this would be greatly appreciated.
ps: The problem happens only on some machines.
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