device polling takes more CPU hits??

Don Bowman don at
Mon Jul 26 13:29:00 PDT 2004

From: Luigi Rizzo [mailto:rizzo at]
> On Mon, Jul 26, 2004 at 01:18:46PM -0700, Kelly Yancey wrote:
> ...
> >   Out of curiousity, what sort of testing did you do to 
> arrive at these
> > settings?  I did some testing a while back with a SmartBits 
> box pumping
> > packets through a FreeBSD 2.8Ghz box configured to route 
> between two em
> > gigabit interfaces; I found that changing the burst_max and 
> each_burst
> > parameters had almost no effect on throughput (maximum 1% 
> difference).
> fast boxes are pci-bus limited, not CPU limited(*) so 
> changing the burst
> size (which basically amortizes some CPU costs) has little if any
> effect.

The PCI-X bus will probably be 64-bit 133MHz in this case,
the limit moves up to the P64H2 hub for large packets,
to the CPU for small packets. Polling becomes quite
critical to prevent livelock.


More information about the freebsd-net mailing list