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Re: Very slow network performance with KVM using virtio and tap.



Robert, following http://www.howtoforge.com/virtualization-with-kvm-on-a-debian-squeeze-server
i reach to the conclusion that using kvm network config is "troublesome".
I ended using "--network=bridge:br0 " on startup the vm, with qemu .

Anyway, from another squeeze (my work computer), installed Virtual machine manager and never
looked back. virsh never worked right for me .

Regards.

Pablo Sánchez

PS: http://www.techotopia.com/index.php/Creating_Xen_and_KVM_RHEL_5_Virtual_Machines_from_the_Command-line_%28virt-install_and_virsh%29
was also helpful


I have tried a KVM setup 2 different ways.  The first was using a straight bridge without using tap at all.  The WinXP VM is using the latest known version of the virtio drivers.  The bridge is on a gigabit nic. 

The second setup was using a bridge containing a tap0 interface and using the tap0 interface in the KVM config. 


I have tested network speeds from the host with other machines in the network using iperf.  Bridge interface to other machine on the network is fast with with speeds you would expect from using 1G nics.  Using the same iperf tests, I get about 1/100 of the speed when using the bridge or tap0 interfaces with the virtio nic.  WinXP shows the virtio nic as being 1 Gbps device.

I am including some of my config below.  Anyone have suggestions on how to get greater than 1MBs transfer rates when using KVM in a bridged setup?



####interfaces####
iface br0 inet static
        address 192.168.0.155
        network 192.168.0.0
        netmask 255.255.255.0
        broadcast 192.168.0.255
#        gateway 192.168.0.1
        bridge_ports eth3 tap0
        bridge_stp off
        bridge_maxwait 0
        bridge_fd 0
        pre-up /usr/sbin/tunctl -u libvirt-qemu -t tap0
        pre-up ifconfig tap0 up
        post-down ifconfig tap0
####interfaces####


###libvirt xml file###
<domain type='kvm'>
  <name>WINXPVM</name>
  <uuid>f1340442-6088-11e0-a43a-001b214871e8</uuid>
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc-0.12'>hvm</type>
    <boot dev='cdrom'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/kvm/WINXP/WINXP.img'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' unit='0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/kvm/iso/WINXP-PRO-SP3-VIRTIO.iso'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='ethernet'>
      <mac address='de:ad:be:ef:9a:9e'/>
      <target dev='tap0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='tablet' bus='usb'/>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='29005' autoport='no' keymap='en-us'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

###libvirt xml file###



    
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