Virtio: Difference between revisions

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= Paravirtualized drivers for kvm/Linux =
* Virtio was chosen to be the main platform for IO virtualization in KVM
* The idea behind it is to have a common framework for hypervisors for IO virtualization
* More information (although not uptodate) can be found in kvm [http://kvm.qumranet.com/kvmwiki/KvmForum2007?action=[[AttachFile]]&do=get&target=kvm_pv_drv.pdf pv driver]
* At the moment network/block/balloon devices are suported for kvm
* The host implementation is in userspace - qemu, so no driver is needed in the host.
 
= How to use Virtio =
* Get kvm version >= 60
* Get Linux kernel with virtio drivers for the guest
** Get Kernel >= 2.6.25 and activate (modules should also work, but take care of initramdisk)
*** CONFIG_VIRTIO_PCI=y (Virtualization -> PCI driver for virtio devices)
*** CONFIG_VIRTIO_BALLOON=y (Virtualization -> Virtio balloon driver)
*** CONFIG_VIRTIO_BLK=y (Device Drivers -> Block ->  Virtio block driver)
*** CONFIG_VIRTIO_NET=y  (Device Drivers -> Network device support -> Virtio network driver)
*** CONFIG_VIRTIO=y  (automatically selected)
*** CONFIG_VIRTIO_RING=y (automatically selected)
*** you can safely disable SATA/SCSI and also all other nic drivers if you only use VIRTIO (disk/nic)
* As an alternative one can use a standard guest kernel for the guest > 2.6.18 and make use sync backward compatibility option
** Backport and instructions can be found in [http://www.kernel.org/pub/scm/virt/kvm/kvm-guest-drivers-linux.git kvm-guest-drivers-linux.git]
* Use model=virtio for the network devices and if=virtio for disk
** Example
<pre><nowiki>
qemu/x86_64-softmmu/qemu-system-x86_64 -boot c -drive file=/images/xpbase.qcow2,if=virtio,boot=on -m 384 -net nic,model=virtio -net tap,script=/etc/kvm/qemu-ifup
</nowiki></pre>
* -hd[ab] for disk won't work, use -drive
* Disk will show up as /dev/vd[a-z][1-9], if you migrate you need to change "root=" in Lilo/GRUB config
* At the moment the kernel modules are automatically loaded in the guest but the interface should be started manually (dhclient/ifconfig)
* Currently performance is much better when using a host kernel configured with CONFIG_HIGH_RES_TIMERS. Another option is use HPET/RTC and -clock= qemu option.
* Expected performance
** Performance varies from host to host, kernel to kernel
** On my laptop I measured 1.1Gbps rx throughput using 2.6.23, 850Mbps tx.
** Ping latency is 300-500 usec
* Enjoy, more to come :)
 
__NOTOC__

Revision as of 13:09, 2 December 2008

Paravirtualized drivers for kvm/Linux

  • Virtio was chosen to be the main platform for IO virtualization in KVM
  • The idea behind it is to have a common framework for hypervisors for IO virtualization
  • More information (although not uptodate) can be found in kvm AttachFile&do=get&target=kvm_pv_drv.pdf pv driver
  • At the moment network/block/balloon devices are suported for kvm
  • The host implementation is in userspace - qemu, so no driver is needed in the host.

How to use Virtio

  • Get kvm version >= 60
  • Get Linux kernel with virtio drivers for the guest
    • Get Kernel >= 2.6.25 and activate (modules should also work, but take care of initramdisk)
      • CONFIG_VIRTIO_PCI=y (Virtualization -> PCI driver for virtio devices)
      • CONFIG_VIRTIO_BALLOON=y (Virtualization -> Virtio balloon driver)
      • CONFIG_VIRTIO_BLK=y (Device Drivers -> Block -> Virtio block driver)
      • CONFIG_VIRTIO_NET=y (Device Drivers -> Network device support -> Virtio network driver)
      • CONFIG_VIRTIO=y (automatically selected)
      • CONFIG_VIRTIO_RING=y (automatically selected)
      • you can safely disable SATA/SCSI and also all other nic drivers if you only use VIRTIO (disk/nic)
  • As an alternative one can use a standard guest kernel for the guest > 2.6.18 and make use sync backward compatibility option
  • Use model=virtio for the network devices and if=virtio for disk
    • Example
qemu/x86_64-softmmu/qemu-system-x86_64 -boot c -drive file=/images/xpbase.qcow2,if=virtio,boot=on -m 384 -net nic,model=virtio -net tap,script=/etc/kvm/qemu-ifup
  • -hd[ab] for disk won't work, use -drive
  • Disk will show up as /dev/vd[a-z][1-9], if you migrate you need to change "root=" in Lilo/GRUB config
  • At the moment the kernel modules are automatically loaded in the guest but the interface should be started manually (dhclient/ifconfig)
  • Currently performance is much better when using a host kernel configured with CONFIG_HIGH_RES_TIMERS. Another option is use HPET/RTC and -clock= qemu option.
  • Expected performance
    • Performance varies from host to host, kernel to kernel
    • On my laptop I measured 1.1Gbps rx throughput using 2.6.23, 850Mbps tx.
    • Ping latency is 300-500 usec
  • Enjoy, more to come :)


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