Comment by romka2

I would agree with this sentence if "optimizing" were replaced with "making marketing claims". Optimization is the process of finding the fastest implementation. In the case of ListDir each successive version is faster than the last on a benchmark with warm IO caches, therefore it'll be faster on the same benchmark with cold IO caches (this is not a general claim; I'm talking specifically about ListDir). Benchmarking with warm IO caches is easier (invalidating caches is generally very difficult) and yields more reliable and more actionable results, hence it's better to benchmark with hot caches. It has nothing to do with the average vs worst case.