[Soekris] Net 4801 performance

[Stuart Henderson]

On 2006/09/06 09:40, Stefano & Alberto wrote:
> 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 

Polling on FreeBSD should do something similar. I think there's
an option tucked away somewhere in m0n0wall to enable this.
It's not on by default because it can increase network latency,
but that's probably better than the alternative here.

> 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...

I read http://www.larwe.com/technical/geode_linux.html
(paragraph starting "The second attack method" at the bottom)
which talked about using different VSA code which helped
with interrupt latency for audio - though it looks like
they use soundblaster emulation which is done in VSA, so it
might not help at all for normal PCI devices.

Obviously we can't swap VSAs with those from Award BIOS
devices as easily as described though. And I guess if it
were that simple it would have been done long ago...

(aiui, VSA is system code loaded by the BIOS before
devices are initialized, running all the time on the cpu
at higher priority than kernel code, handling system
management tasks, including device emulation, I guess
power management, PCI bus access, etc: some embedded
systems designer familiar with Geode architecture may
be able to fill in more details).

Something interesting came up recently, OLPC ("one laptop
per child" aka $100 laptop) are using Geode systems, and
though some of the device emulation (VESA/souundblaster)
won't be available, there is some talk of other parts of
VSA becoming open-source:

http://mailman.laptop.org/pipermail/devel-boards/2006-August/000001.html

Reading more about OLPC/linuxbios I found this in a mailing
list post: "there is basically no PCI system in the Geode GX.
All PCI configuration space registers are emulated by VSA.
It is possible to have a heavily modified driver to access
the MSR register space than the emulated PCI space but it
requires a lot of work".

No simple improvements, but I think this goes some way towards
explaining things a bit better.

> And, since i need the board to handle high throughput traffic, is there 
> a better board than net4801?

There are faster SBC but there are always trade-offs...