On 16.04.2012 13:01, Stefan Pietsch wrote: > On 12.04.2012 09:42, Hans-Kristian Bakke wrote: >> Hi >> >> For some reason I am not able to get good network performance using >> virtio/vhost-net on Debian KVM host (perhaps also valid for Ubuntu >> hosts then). >> 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. > > [......] > >> I have tried: >> ---------------- >> - Replacing Debian Wheezy with Debian Squeeze (stable, kernel >> 2.6.32-xx) - even worse results >> - 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 >> - ...in addition to exchanging Debian with Fedora 17 alpha, Proxmox >> 1.9 and 2.0 and ESXi 5 which all have expected network performance >> using virtio. >> >> So, I am at a loss here. I does not seem to be kernel config related >> (as using Fedoras config on Debian kernel source didn't do anything >> good) so I think it must be either a kernel patch that red hat kernel >> based distros uses to make virtio/vhost much more efficient or perhaps >> something with Debians qemu-version, bridging or something. Hans-Kristian submitted a bugreport to Debian BTS about this, http://bugs.debian.org/668594 . In this case it turns out to be a problem with particular qemu-kvm userspace binary build, maybe the toolchain used, maybe something else - I don't yet know. This is not the first time this version is mentioned as being slow (slower) with network transfers, here's another bugreport which I merely ignored till now -- see http://bugs.debian.org/665046 . I'm working on this, or trying to anyway. > I have made some tests with a Debian Squeeze KVM host running with the > Linux Kernel 2.6.39 from backports and the Kernel version 2.6.32-11-pve > from Proxmox. > > (http://download.proxmox.com/debian/dists/squeeze/pve/binary-amd64/pve-kernel-2.6.32-11-pve_2.6.32-66_amd64.deb) These are very different. Note that 2.6.32 does not have vhost-net support which is used by Hans-Kristian and speeds up network operations dramatically. > Network performance between two virtual machines on the same host is > significantly slower with the Debian kernel: > > 2.6.39-bpo.2-amd64 : 1.31 Gbits/sec > 2.6.32-11-pve : 2.20 Gbits/sec Please try current debian kernel. There were a few issues with that 2.6.32 backport, but I don't know the details and don't know if these affects qemu/kvm in any way or not. And again, if you really want good networking speeds, you should use vhost-net which is is not supported by 2.6.32 kernel. > iperf tests between a virtual machine and the KVM host connected to the > same local bridge interface showed similar results. > > Are there other people who can confirm this? Thanks, /mjt -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
