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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
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| * The host implementation is in userspace - qemu, so no driver is needed in the host.
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| == How to use Virtio ==
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| * Get kvm version >= 60
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| * Get Linux kernel with virtio drivers for the guest
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| ** Get Kernel >= 2.6.25 and activate (modules should also work, but take care of initramdisk)
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| *** CONFIG_VIRTIO_PCI=y (Virtualization -> PCI driver for virtio devices)
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| *** CONFIG_VIRTIO_BALLOON=y (Virtualization -> Virtio balloon driver)
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| *** CONFIG_VIRTIO_BLK=y (Device Drivers -> Block -> Virtio block driver)
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| *** CONFIG_VIRTIO_NET=y (Device Drivers -> Network device support -> Virtio network driver)
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| *** CONFIG_VIRTIO=y (automatically selected)
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| *** CONFIG_VIRTIO_RING=y (automatically selected)
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| *** you can safely disable SATA/SCSI and also all other nic drivers if you only use VIRTIO (disk/nic)
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| * As an alternative one can use a standard guest kernel for the guest > 2.6.18 and make use sync backward compatibility option
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| ** 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]
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| * Use model=virtio for the network devices and if=virtio for disk
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| ** Example
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| <pre><nowiki>
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| 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
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| </nowiki></pre>
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| * -hd[ab] for disk won't work, use -drive
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| * Disk will show up as /dev/vd[a-z][1-9], if you migrate you need to change "root=" in Lilo/GRUB config
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| * At the moment the kernel modules are automatically loaded in the guest but the interface should be started manually (dhclient/ifconfig)
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| * 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.
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| * Expected performance
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| ** Performance varies from host to host, kernel to kernel
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| ** On my laptop I measured 1.1Gbps rx throughput using 2.6.23, 850Mbps tx.
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| ** Ping latency is 300-500 usec
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| * Enjoy, more to come :)
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| __NOTOC__ | | __NOTOC__ |