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* Virtio was chosen to be the main platform for IO virtualization in KVM
* 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
* The idea behind it is to have a common framework for hypervisors for IO virtualization
* More information (although not uptodate) can be found [[Media:KvmForum2007$kvm_pv_drv.pdf|here]]
* The specification can be found here: https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
* 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 virtio-net-pci device for the network devices (or model=virtio for old -net..-net syntax) and if=virtio for disk
** Example
<pre><nowiki>
x86_64-softmmu/qemu-system-x86_64 -boot c -drive file=/images/xpbase.qcow2,if=virtio -m 384 -netdev type=tap,script=/etc/kvm/qemu-ifup,id=net0 -device virtio-net-pci,netdev=net0
</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 :)


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Latest revision as of 10:38, 15 December 2022

Virtio

Paravirtualized drivers for kvm/Linux