Underutilisation of CPU --- am I PCI bus bandwidth limited?

[Don Bowman]

From: lukem.freebsd at cse.unsw.edu.au
> 
 ...
> 
> This is rather confusing, as I cannot tell if the system is 
> IO bound or CPU 
> bound. Certainly I would not have expected the 133/64 PCI bus 
> to be saturated 
> given that peak throughput is around 550Mbit/s with 1024-byte 
> packets. (Such a 
> low figure is not unexpected given there are 2 syscalls per packet).

You may find you have not loaned the em driver enough buffers,
(max_rxd, max_txd).
you may find you want to use device polling, poll on idle, and
play with the polling parameters.
In this config i have achieved ~2Gbps of throughput with these
large packets, so i know it can be done.