syscall cost freebsd vs linux ?

today i was comparing the performance of some netmap-related code
on FreeBSD and Linux (RELENG_9 vs 3.2) and i was surprised to see that
our system calls are significantly slower.
On comparable hardware (i7-2600k vs E5-1650) the syscall
getppid() takes about 95ns on FreeBSD and 38ns on linux.

(i make sure not to use gettimeofday(), which in linux is through vdso,
and getpid(), which is cached by glibc).

Any idea on why there is this difference and whether/how
we can reduce it ?

cheers
luigi