device polling takes more CPU hits??

[Kelly Yancey]

On Mon, 26 Jul 2004, Don Bowman wrote:

> From: Luigi Rizzo [mailto:rizzo at icir.org]
> > 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.
>

  Sorry, I should be been more clear.  Polling certainly stopped livelock
under extreme load, however I never found much difference whether the
burst size was small or large.  I was wondering if it was just the nature
of my test and if in other environments the burst_max and each_burst knobs
have a greater affect.

  Kelly

--
Kelly Yancey  -  kbyanc@{posi.net,FreeBSD.org}  -  kelly at nttmcl.com
FreeBSD, The Power To Serve: http://www.freebsd.org/