Consider a faster clock

[ahacking]

Consider use of clock_gettime(CLOCK_MONOTONIC_COARSE, &ns) which may provide a lower overhead clock vs gettimeofday().

This Stack overflow answer provides some indicative cycle counts:

gettimeofday (us) => 42 cycles

clock_gettime (ns) => 9 cycles
(CLOCK_MONOTONIC_COARSE)

The use of CLOCK_MONOTONIC_COARSE is supported on Linux and FreeBSD, but is an extension to POSIX from what I can tell with 1ms resolution and uses the VDSO library to avoid kernel calls.

Given the extension only needs millisecond resolution it doesn't diminish the accuracy using the faster coarse grained clock.

So a portability #ifndef will undoubtedly be required to fall back to CLOCK_MONOTIC on systems that don't define the coarse clock.