> > It's the DMA bandwidth saved, most of the specweb runs on x86 hardware
> > is limited by the DMA throughput of the PCI host controller. In
> > particular some controllers are limited to smaller DMA bursts to
> > work around hardware bugs.
> I'm not sure that's entirely true in this case - the Netfinity
> 8500R is slightly unusual in that it has 3 or 4 PCI buses, and
> there's 4 - 8 gigabit ethernet cards in this beast spread around
> different buses (Troy - are we still just using 4?
My machine is not exactly an 8500r. It's an Intel pre-release
engineering sample (8-way 900MHz PIII) box that is similar to an
8500r... there are some differences when going across the choerency
filter (the bus that ties the two 4-way "halves" of the machine
together). Bill Hartner has a test program that illustrates the
differences-- but more on that later.
I've got 4 PCI busses, two 33 MHz, and two 66MHz, all 64-bit.
I'm configured as follows:
PCI Bus 0 eth1 --- 3 clients
33 MHz eth2 --- Not in use
PCI Bus 1 eth3 --- 2 clients
33 MHz eth4 --- Not in use
PCI Bus 3 eth5 --- 6 clients
66 MHz eth6 --- Not in use
PCI Bus 4 eth7 --- 6 clients
66 MHz eth8 --- Not in use
> ... and what's
> the raw bandwidth of data we're pushing? ... it's not huge).
2900 simultaneous connections, each at ~320 kbps translates to
928000 kbps, which is slightly less than the full bandwidth of a
single e1000. We're spreading that over 4 adapters, and 4 busses.