it's quite likely slower than need be
because of the wretched TCP_NODELAY
(or whatever it is on your system) not being
set by default.
set it on so as not to delay and it's typically much faster.

term% diff /sys/src/cmd/unix/u9fs/u9fs.c .
33a34
> #	include	<netinet/tcp.h>
1247a1249
> #ifdef SO_KEEPALIVE
1248a1251,1254
> #endif
> #ifdef TCP_NODELAY
> 	setsockopt(0, IPPROTO_TCP, TCP_NODELAY, (char*)&on, sizeof(on));
> #endif

i also ifdef'd SO_KEEPALIVE because some systems haven't got it.

i changed the old (2nd edition) version of u9fs to
emulate file server permissions and permission checking
more precisely, which is to say that it must have been
missing something, but i haven't had the need for that
this time.  you might find you need to adjust it though.
i haven't got that source or i'd hand it on.