// 100µs is enough to amortize the overhead and provide sufficient
	// dynamic load balancing.
	grain := uint64(0)
	if b.previousN > 0 && b.previousDuration > 0 {
		grain = 1e5 * uint64(b.previousN) / uint64(b.previousDuration)
	}
	if grain < 1 {
		grain = 1
	}
	// We expect the inner loop and function call to take at least 10ns,
	// so do not do more than 100µs/10ns=1e4 iterations.