As a part of cargo crev I was reviewing this crate in version 1.10.1 . All was good, but I have one idea.

It seems like on Windows this crate calls the GetLogicalProcessorInformation twice. Any reason not to start with a buffer of a fix size (eg. 64 entries)? Maybe this initial buffer could be on stack, so it wouldn't really cost anything. On most machines that would cut the number of calls to just 1.