[AusNOG] Tech Q: Looking for Cheapest 10G Switches for Hobby Lan.

[Mark Smith]

On Sun, 18 Jul 2010 19:50:22 +1000
Narelle <narellec at gmail.com> wrote:

> On Sat, Jul 17, 2010 at 10:20 AM, Mark Smith
> <nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
> > Want to make their head explode? In some experimentation a while back, I
> > measured latency of packet processing of an old Netgear FA312 100Mbps
> > NIC in a P3 450Mhz, verses an Intel 1Gbps PCIe in a Q6600 quad core. The
> > Netgear had lower latency, and IIRC, significantly lower latency. Of
> > course, all those measurements were in microseconds, and therefore
> > probably irrelevant to actual gaming, but I don't think they actually
> > care. The length of the cable was measurable too at that scale. (If you
> > get pictures of a fight breaking out at a LAN party over old 100Mbps
> > NICs, and who's sitting closest to the switch, send them to me
> > please :-) )
> 
> How did you measure this?
> 

You could probably do it using conventional IP pings, I was doing it
while testing an implementation of the Ethernet v2.0 Configuration
Testing Protocol I wrote for the Linux kernel, which basically provides
ethernet layer ping, so didn't have the overheads of IP packet
processing or firewalling. I ran a tcpdump on the interface in question,
and then compared the in and out timestamps. I think it was also
measuring the effects of the CPU instruction case. IIRC, with a fast
packet rate, the first in/out difference was around 40 microseconds,
then would drop to between 4 and 8 microseconds. My guess at the time
was that the fast packet rate was keeping the protocol code in the
instruction cache. I didn't investigate further. Measuring in/out time
differences at the source interface, subtracting in/out latency on the
destination interface, indicated cable and/or switch latency.

> In all of this discussion (great btw) the actual software architecture
> hasn't really been mentioned. IME that's usually where all the
> bottlenecks come from, rarely the LAN...
> 
> 
> -- 
> 
> 
> Narelle
> narellec at gmail.com