On 13.04.2012 13:46, Hans-Kristian Bakke wrote: > Package: qemu-kvm > Version: 1.0+dfsg-9 > Severity: normal > > I cannot get optimal network througput on KVM guest using Debian Wheezy (and > stable) as KVM host. > It is not horribly bad, just not good compared to relevant alternatives. > > I have tried Ubuntu Server 11.10, Proxmox 1.9, Proxmox 2.0 and Fedora 17 > Alpha as 1:1 replacement for the Debian KVM host using the same guests (just > preserving the LVM volumes between installs) and they all manage about 20 > gbit/s guest to guest using a simple iperf test, while Debian only manages > about 2.3 gbit/s with high CPU usage. The CPU usage is generally much higher > on all guest network activity on Debian and are in some cases not able to > even saturate a gigabit link (when coming from other subnet) without maxing a > CPU core where the other KVM hosts barely breaks a sweat. > > Disc IO is very good and the guests feels snappy so it doesn't seem like > there is something really wrong, just something suboptimal with the > networking. > The issue follows only the host OS as the guests have been the same in all > comparisons (Debian Wheezy) > > > To reproduce: > ------------ > Install Debian Wheezy in guests (minimal with SSH and ntp) > Install iperf via apt-get > Configure network > > Run test: > guest1: iperf -s > guest2: iperf -c <iperf-server> -i 2 -t 33333 > > My results: > ---------------------------- > - Guest to guest performance via local bridge: ~2.3 gbit/s, very high CPU > usage on vhost-$PID and kvm process on host > - Physical server to guest on same subnet: ~940 mbit/s but with very high CPU > usage on vhost-$PID and kvm process on host > - Physical server to guest via router: ~850 mbit/s with very high CPU usage > on vhost-$PID and kvm process on host (why is routed traffic slower than > switched on the guest??) > - Physical server to kvm host via router (just to verify that the router is > not the issue): ~940 mbit/s with almost no CPU usage > > Expected results after comparison with other KVM hosts everything else the > same: > ------------------------- > - Guest to guest performance via local bridge: ~20 gbit/s, high CPU usage > - Physical server to guest on same subnet: ~940 mbit/s with low CPU usage on > vhost-$PID and a bit higher on kvm process on host > - Physical server to guest via router: ~940 mbit/s with low CPU usage on > vhost-$PID and a bit higher on kvm process on host > - Physical server to kvm host via router (just to verify that the router is > not the issue): ~940 mbit/s with almost no CPU usage (the same as my current > results) > > Compare results with other OSes on same machine (guest to guest via bridge): > Ubuntu Server 11.10 (virtualization host): ~19 gbit > Proxmox VE 2.0: ~20 gbit/s > Fedora 17 alpha: ~20 gbit/s
Which versions of qemu[-kvm] are used on these? Did you try older versions of qemu-kvm from snapshot.debian.org? It really looks like qemu-kvm-specific, not kernel-specific, and qemu-kvm in Debian is very close to upstream 1.0.1 version, so I'm not sure where to look at. I've another bugreport at hand claiming that vhost-net, but this time with macvtap not bridge, has a speed regression between 1.0+dfsg-8 and 1.0+dfsg-9 (bridge mode unaffected). 1.0+dfsg-9 is the (debian) revision where I added a 1.0.1 diff (I didn't re-upload the new source). Maybe this is related somehow - please try -8 release too, for comparison. Unfortunately I can't help here at all, as I don't reach any speeds comparable with what you have, and mine don't change much. But I haven't tried installing any other OS (from a list you mentioned too), -- I don't like to repartition my only hdd to do so. > I have tried: > ---------------- > - Replacing Debian Wheezy with Debian Squeeze (stable, kernel 2.6.32-xx) - > even worse results This kernel does not support vhost-net, it was 2.6.35 or .38 addition. > - Replacing kernel 3.2.0-2-amd64 with vanilla kernel 3.4-rc2 and config based > on Debians included config - no apparent change > - Extracted the kernel-config file from Fedora 17 alphas kernel and used this > to compile a new kernel based on Debian Wheezys kernel source - slightly > worse > > results > - Installing Proxmox VE 2.0 kernel in Debian. Results are the same > - ...in addition to exchanging Debian with Ubuntu Server 11.10, Fedora 17 > alpha, Proxmox 1.9 and 2.0 and ESXi 5 which all have expected network > performance using virtio. > > > Please optimize KVM/vhost in Debian so it performs like the other > alternatives. With pleasure, but I need some help ;) Thank you! /mjt -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
