Autotest really slow to detect updates when sharing codebase with VM

Ok I have my dev environment setup like so:

Local machine (OS X) has the codebase and shares via NFS.
VM (Ubuntu) runs the app, has everything setup and mounts the codebase
from the NFS share on the Mac.

I use SSH to run stuff like autotest etc. on my VM and everything
works fine.

However autotest is slow to detect file changes, I just did a couple
of tests:

- saving file in textmate, time for autotest to detect change: 12s,
5s, 8s, 8s
- touching file: 15s, 3s, 6s

It used to be almost instantaneous when I wasn't sharing code like
this, does anyone know of anything I can do to improve the time it
takes autotest to pickup the changes?

Well I changed my shares to use samba and it's a lot better now, dunno
if there is some sort of timeout with NFS that I needed to tweak. It
was very annoying and made autotest pretty pointless.