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It > seems to be Intel PMU specific! Or more accurately, we only observe it on the Intel systems I've checked. The AMD systems record fewer cycle events in mdelay() and thus may not have a chance to skip events. I'll try updating my kernel module to busy wait by looping until jiffies is above a particular value. This would hopefully avoid any CPU-specific idling which would reduce the cycle count on AMD. I'll update this thread with my findings after testing. Thanks again, Stephen