Question

I’m reading the source code of libevent,and when it needs to call epoll_create,it uses
syscall insteaded.

int epoll_create(int size)
{
     return (syscall(__NR_epoll_create, size));
}

Will the latter case give a perfomance improvement?

Answer 1

What you’re seeing is pretty much expected. If you poke around the kernel you’ll see most references to epoll_create() are down in the arch directory, meaning they are very much architecture dependent. As such it’s pretty standard that it can’t be invoked directly from userspace.

As for efficiency, take a look man syscall.

As it states in there:

Often the glibc wrapper function is quite thin, doing little work other than
copying arguments to the right registers before invoking the system call, and
then setting errno appropriately after the system call has returned.

So no, typically there’s no big performance hit by this implementation.