Slow I/O on NetBSD domU (on Debian dom0)

[Stefano Marinelli <postnet%dragas.dyndns.org@localhost>]

Hi,
I have two Xen servers, the first one running Lenny (so Xen 3.2.1) and the 
second one running Squeeze (Xen 4.0.1).
Both of them are running one or more Debian domUs without any particular issue. 
NetBSD PV domUs, instead (tried with a freshly compiled netbsd-5), seem to 
suffer from some I/O performance issues. Every time I start an intensive I/O 
task (like "tar xjvf pkgsrc.tar.bz2"), the NetBSD domU starts to lag. ssh 
connections take ages to be accepted, and generally every task and every 
command seem to be very very slow. This doesn't happen on Linux and the other 
domUs just run without any particular problem, they can also do intensive  I/O 
tasks without any problem.
Any suggestion?
I've also a NetBSD 5.1 Dom0 (Xen 3.3) with some NetBSD PV domUs and some Debian 
Linux PV domUs. I cannot test it now, but I never noticed something like that.

Thank you,
Stefano