FreeBSD 7.1-RC1 rl0 watchdog timeout with custom kernel

[Gennady Kudryashoff]

 From Lowell Gilbert <freebsd-questions-local at be-well.ilk.org>:

> > rl0: link state changed to UP
> > rl0: watchdog timeout
> > rl0: watchdog timeout
> >
> > Any mistake?
> 
> The rl driver supports some really terrible hardware, so I'm far from
> convinced that your custom kernel is causing the problems.  Perhaps you
> could check by switching back to a GENERIC kernel for a while.

It works well with GENERIC when I'm simply serfing the net or
fetching ports.
How can I test my network adapter under heavy load?