massive performance drop after a while when using virtio nics

Fabian Deutsch
2008-08-23T19:22:00Z

Hey.

When running a guest in the following setup, I observ a "massive"
performance decrease after a couple of gigabytes of transfrerred data.

other guests keep running fine (no regressions) and nothing unusual is
observed on the host.

fedora 8 host, kvm-72 (user and module)

fedora 9 guest, all updates.
nic 0, vtio:
subnet a
samba listening

nic 1, vtio:
subnet b
iscsi initiator running

samba shares a mount point, pointing to an iscsi target.

now pulling/pushing about 80GB over samba results in a drop from about
60/70Mbit to about 1/2Mbit of troughput.

The problem is reproducible.
The problem is solved after a reboot of the guest. Just restarting
networking doesn't help.
Guest's dmesg doesn't say anything about problems. No errors in
ifconfig.

Has someone observed something similar?

Greetings
- fabian