[maxhou]

Yes they do.

A read() syscall takes longer than a getpid() syscall because read() has more work to do, it actually does a data copy of len bytes, which takes some time (and will be faster/slower if data is cache hot)

What we call the "syscall overhead" is what happens before and after the actual data copy, switching between user and kernel mode.

You make that overhead negligible by calling read() with a large size.