Network performance with vhost=on is extremely bad if a guest uses multiple cores:
HOST kernel: RHEL 2.6.32-279.11.1.el6 KVM 1.2.0 GuestOS: Debian Squeeze (amd64 or 686), CentOS 6.2 Test with something like (install Debian Squeeze first): ./x86_64-softmmu/qemu-system-x86_64 -smp sockets=1,cores=2 -m 512 -hda debian-squeeze-netinst.raw -netdev type=tap,id=net0,ifname=tap111i0,vhost=on -device virtio-net-pci,netdev=net0,id=net0 Downloading a larger file with wget inside the guest will show the problem. Speed drops from 100MB/s to 15MB/s. Can someone reproduce that bug? Any ideas how to fix that? - Dietmar
