Very slow KVM in Ubuntu 12.04

Question

I use Ubuntu 12.04 64-bit and KVM, my CPU is Core i5 3.3 GHz and I have 8 GB of DDR3 RAM. I run Windows 7 in KVM and it's extremely slow. My co-worker use Debian on the same PC configuration and can run Windows 7 extremely fast! Where can be my problem?

[guyfawkes@guyfawkes-pc ~/work]$ sudo cat /etc/libvirt/qemu/windows.xml
<!--
WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE 
OVERWRITTEN AND LOST. Changes to this xml configuration should be made using:
  virsh edit windows
or other application using the libvirt API.
-->

<domain type='kvm'>
  <name>windows</name>
  <uuid>5c685175-baea-0ca6-591f-8269d923ffb8</uuid>
  <memory>2097152</memory>
  <currentMemory>2097152</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='localtime'/>
  <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='/var/lib/libvirt/images/windows.img'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='network'>
      <mac address='52:54:00:94:63:91'/>
      <source network='default'/>
      <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='-1' autoport='yes'/>
    <sound model='ich6'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </sound>
    <video>
      <model type='vga' vram='262144' 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>

UPD: I've enabled Intel-VT before installing KVM. I've successfully installed VirtIO drivers, and it gave me a few of performance, but, for example, when I open Firefox in Windows, even mouse moves very slowly, and GUI is very slow too.

Answer 1

For a start, you've got the VM configured to be emulating an IDE bus, which is pretty slow. Try changing it to a SATA bus.

Better yet, install the virtio drivers in Windows 7, and change it to a virtio bus.

NOTE: Windows may complain about the hardware being changed underneath it, and may have difficulty finding the boot disk after it has changed from IDE to SATA or Virtio.

Similarly, you will get improved network performance if you change the NIC type to virtio.

What version of KVM and kernel are you running on ubuntu? And what version of same on debian?

One other thing worth checking is: is your co-worker using a disk-image for the VM, same as you are, or are they using a raw disk partition or an LVM volume or similar? disk-images are very slow compared to partitions or LVM.

Answer 2

You should install VirtIO drivers under Windows. You can download drivers built by Fedora or build your own from source, see the KVM documentation for information.

Answer 3

I also had incredibly slow performance with my virtual HDD.
The following setting on new HDD corrected everything:

• Storage format: raw
• Cache mode: none (not default!)
• I/O mode: native