If you use "pmtmr" try to reboot with kernel option "clock=tsc".
That's dangerous advice - when the system choses not to use
TSC it often has a reason.
On my Opteron AMD system i normally can route 400 kpps, but with
timesource "pmtmr" i could only route around 83 kpps. (I found the timer
to be the issue by using oprofile).
Unless you're using packet sniffing or any other application
that requests time stamps on a socket then the timer shouldn't
make much difference. Incoming packets are only time stamped
when someone asks for the timestamps.
-Andi