[gentoo-amd64] Unexpected side effect of GCC 4

[Peter Humphrey <prh@gotadsl.co.uk>]

I have a firewall between my ADSL modem and my local network (running 
Gentoo, naturally), and I use it as an rsync server for portage on the 
network. Specifically, the firewall runs emerge --sync in a cron job every 
morning before I get up, then I synchronise my laptop and desktop systems 
from that at my convenience.

The rsync phase of update over the local network has been extremely slow; I 
couldn't get traffic flowing faster than about 30 - 40 kBps on average, and 
the hub showed tremendous numbers of collisions. I did manage to speed it 
up a bit by changing the /usr/portage partition on the server to reiserfs, 
but that improvement seemed to go away again. Meanwhile, other traffic over 
the network went at full speed, about 270 kBps, with only the occasional 
collision.

Now that I've finally managed to build a full system using GCC 4.1.1 on the 
workstation, I find its rsync traffic has leapt to full speed with no 
collisions to speak of. I'm not complaining, mind, but this is a puzzle. As 
far as I know I haven't changed anything else - certainly the firewall box 
has been running continuously throughout.

The speeds I mention are as shown by gkrellm (a very useful utility). The 
network drivers are a module on the workstation (tg3) and built-in on the 
firewall (8139too). The CFLAGS are "-O2 -march=k8 -pipe" on the firewall 
and the set offered by Duncan recently on the workstation.

Any ideas, anyone?

-- 
Rgds
Peter
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