[netperf-talk] Confusing result of the throughput in wireless network with different UDP packet length.

[Andrew Gallatin]

Peng Wang wrote:

> The benchmark platform I use contains two buffalo wireless g router. One
> router is the sender, and one is the receiver. The operating system in
> them is Linux with 2.4.7 version kernel.
>
> The result of the benchmark confuses me. From the following figure we
> can see that the throughput is highest when the UDP packet size is about
> 20k bytes which is much bigger than the MTU. I guess it is because of
> the buffer in the system, but I am not quite sure. Do you see it before?
> Could you explain it?

I'm not at all familiar with performance characteristics of
wireless networks, but on fast (10GbE) wired networks I
sometimes see similar behavior when the host has expensive
system calls.   The larger the message size, then the more data
is written on the socket using a single system call.

So, a few questions:

1) Does a test via a 100Mb or 1Gb connection between the routers show
   the same characteristic?   How about a local (loopback) test
   from a machine to itself?

2) Have you measured the system call overhead using something like
   lmbench?

Drew