AFAICT that is a command line answer, which is not really what I want, since it may be OS dependent, and I want to get this inside my timing code. I have ended up with code like this (My tsc_tick_count is a class which reads and stores TSC; its default constructor saves "now).
static double measureTSCtick() {
// Use C++ "steady_clock" since cppreference.com recommends against
// using hrtime. Busy wait for 100ms based on the std::chrono clock
// and time that with rdtsc.
auto start = std::chrono::steady_clock::now();
tsc_tick_count startTick;
auto end = start + std::chrono::milliseconds(100);
while (std::chrono::steady_clock::now() < end) { }
auto elapsed = tsc_tick_count::now() - startTick;
// We should maybe read the actual end time here, but this seems
// to work OK without that. (And, if we're worried about
// our thread being stolen for a while, that could happen between the
// rdtsc and reading this clock too...)
double tickTime = 100.e-3 / elapsed.getValue();
return tickTime;
}
which works but takes 1/10s rather than a few us which one might expect this to take at worst.
