Function monotonic_ns 

pub fn monotonic_ns() -> u64

Nanoseconds on the host’s CLOCK_MONOTONIC, what clock_gettime gives a process in any language.

Unlike Instant, which has no portable epoch, this is comparable between processes on one host, so two nodes can put their samples on one timeline without exchanging anything. It counts from boot, does not step with the wall clock, and 0 means the call failed, which on Linux it does not.