For the past few months I’ve been suffering with noticeably slow network speeds on my battered Thinkpad. It’s running almost 24/7 as an rtorrent slave, so the crappy performance wasn’t really a big deal, and that’s why I didn’t chase it very much. I don’t really care if I seed the Ubuntu 8.04.1 ISOs at 2kbps or 20, since I’m only doing it to help out.
Yesterday I noticed this bug report for Ubuntu, which rather tersely mentions network speeds on the 2.6.2? kernel. Apparently, if the comments are correct, one of the sysctl.conf options is set in a way that can interfere with performance.
Mind you that laptop is running Arch, and the network port is nothing spectacular anyway, but installing procps (which owns the sysctl framework) and adding this line to /etc/sysctl.conf
net.ipv4.tcp_window_scaling = 0
doubled the download and upload speeds in rtorrent. Of course, they were rather paltry to start with, so doubling them isn’t that spectacular, but at least I’m getting total download speeds in the 50-60kbps range, when they were barely peaking at 12kbps before.
I can’t guarantee it’s a winner for every system, but I’ve added it to two Arch systems and an Ubuntu one, and it doesn’t seem to hurt anything. First thing, do no harm. 
Jeez… I gotta keep tabs on this one, too.
It didn’t double my rtorrent speeds, it quadrupled them. Thanks!