I did benchmarks on OS X (10.5) between asynchronous IO, mmap, stdio, and normal unix open/read (disabling caching) — it all came down to about the same after I

I did benchmarks on OS X (10.5) between asynchronous IO, mmap, stdio, and normal unix open/read (disabling caching) — it all came down to about the same after I had fiddled with page size, prefetch size, etc. to optimize each. This of course depends on your OS (and version). My advice would be to pick API based on “semantics” (or need for portability). If you need to read through a file, use the API intended for that because mmap will not be optimized for that access pattern, but stdio will.