> On Mon, Nov 5, 2012 at 12:51 PM, Dietmar Maurer > <diet...@proxmox.com> wrote: > > 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? > > Which exact QEMU are you using: qemu or qemu-kvm? Distro package or > from source? Any patches applied?
qemu-kvm 1.2, compile from source (no patches) I would also try with latest qemu, but seem qemu site is down? > Was performance better in previous versions? We observed the problem only with version 1.2. > Is the network path you are downloading across reasonably idle so that you > get reproducible results between runs? Sure. Using vhost=on drops performance from 100MB/s to 15MB/s.
