I think on newer x86 chips the ‘cycle’ counter increments at a ~constant rate, rather than changing with variable cpu frequencies. There’s a cpuid flag for this

I think on newer x86 chips the ‘cycle’ counter increments at a ~constant rate, rather than changing with variable cpu frequencies. There’s a cpuid flag for this and I think Linux exposes it in procfs somewhere too. Older chips do have the problem you describe, as well as problems with cycle counts diverging (or never being close) between cores/sockets. It still isn’t exact in the way you describe. The most reasonable thing you can do is regularly calibrate based on an actual clock (whose rate also gets calibrated based on ntp…) to have a cycles<->ns conversion factor.