[Soekris] Net 4801 performance

[Stefano & Alberto]

Stuart Henderson wrote:
> These are _low-power_ boxes, not quick boxes. PCI throughput seems
> particularly low compared to a standard PC (most of the cpu time
> will be spent in interrupt processing). 
I have tested a net4801 with different OS (PicoDebian Linux, Voyage 
Linux, M0n0wall BSD) and gathered throughput performance with all of 
these. The best result i've come up with is with PicoDebian Linux, 
kernel 2.6.17.7, with wich i've achieved 55Mbit/s measured with the 
"iperf" tool. Using an older kernel (2.6.15) i could achieve up to 
30Mbit/s, and the reason of this is that with the 2.6.17 kernels they 
have changed the network drivers for NatSemi (National Semiconductor), 
supporting NAPI in order to generate less interrupts 
(http://lwn.net/Articles/30107/ ). In fact it appeared that under heavy 
loads of network traffic, the cpu goes to 99% usage due to interrupt 
handling. Such information can be seen through the "top" tool, in 
particular looking at the hi%(hardware interrupts) and si%(software 
interrupts).

I have performed the same measurements with an old 486 PC (should be the 
same architecture as Soekris' Geode, right?) with NatSemi PCI cards, and 
i've measured around 85Mbit/s... does anyone know why there's this big 
difference? I expected the Soekris board to have similar performance as 
a PC with similar processor...
And, since i need the board to handle high throughput traffic, is there 
a better board than net4801? Or should i move to a different 
architecture (Mipsel, Arm....)?
Thanks in advance