Depends on the use case; keep in mind that syscalls are slow, too. If you have an application that does significant computation on lots of data (think a scientific calculation/simulation), having another core on the same socket read ahead from disk to RAM might be much more efficient than pausing computation to read synchronously. Or if you're a file server that is just passing things back to the kernel's network layer, you might not even need to see the contents of RAM yourself.