Network problems with VIA chipset and Athlon XP

[Michael Stein]

>  The system setup is as follows: A beowulf cluster composed of 16 nodes and 
> one master machine connected to a 3Com (3C17203) 24 Port 100Mbit ethernet 
> switch. The nodes are all identical and use an Asus A7V266-EX motherboard 
> (VIA KT266), Athlon XP 1800+ CPU, 1.5GB of PC2100 DDR RAM, a 40GB Seagate IDE 
> disk, Accton EN-1216 10/100 NIC (Tulip) and ATI Rage XL AGP graphics card. 

I'd guess it's the VIA KT266 chipset.

I have 3 machines with AMD Athlon 2100+ XP and ASUS A7V266-E motherboards.
I recently replaced each Netgear tulip NIC with a Intel Intel PRO/1000 T
Desktop adapter PWLA8390T.

The best I've seen these machines do between identical machines is 153
Mbps.  One of these A7V266-E machines to/from a 1 Ghz P3 on a ASUS CUSL2-C
with the same NIC can do:

A7V266-E to CUSL2-C		384 Mbit/second
CUSL2-C to A7V266-E		153 Mbit/second

It isn't the NICs because one of these same Intel GB NICs in a dual AMD
TYAN S2462 machine (1U) can do 700 to 800 Mbps either way even though
these are only 32 bit PCI cards.  (And the NICs were only $48).

There are some comments on what might be the problem at:
http://www.cicese.mx/~mirsev/Linux/VIA/VIA-latency-linux.html
"PCI latency" patch for Linux (for KT266A chipset only)

When I tried the patch it didn't help my bandwidth problem and I haven't
had anymore time to look into this.  The people using those three machines
think the increase from 90 Mbps to 150 Mbps is great.  That really makes
me wonder what they would think of 800 to 900 Mbps (or perhaps they
have some other bottleneck which would hide more performance?).

If you find out more, please let me know.