pytest-benchmark will run your function multiple times between measurements. A round is that set of runs done between measurements. This is quite similar to the builtin timeit module but it’s more robust.

The problem with measuring single runs appears when you have very fast code. To illustrate:

Diagram illustrating issues with measuring very fast code

In other words, a round is a set of runs that are averaged together, those resulting numbers are then used to compute the result tables. The default settings will try to keep the round small enough (so that you get to see variance), but not too small, because then you have the timer calibration issues illustrated above (your test function is faster than or as fast as the resolution of the timer).

By default pytest-benchmark will try to run your function as many times needed to fit a 10 x TIMER_RESOLUTION period. You can fine tune this with the --benchmark-min-time and --benchmark-calibration-precision options.