From KVM
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= Paravirtualized drivers for kvm/Linux =
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t'''est123'''
* Virtio was chosen to be the main platform for IO virtualization in KVM
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* The idea behind it is to have a common framework for hypervisors for IO virtualization
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* 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]
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* 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__
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Revision as of 12:43, 2 December 2008

test123