• C library, bindings
• Stable API
• Multiple hypervisors
• Host management

<domain type='kvm'>
  <name>fedora</name>
  <uuid>63840878-0deb-4095-97e6-fc444d9bc9fa</uuid>
  <memory unit='KiB'>1048576</memory>
  <vcpu>2</vcpu>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk/>
    <interface/>
    <hostdev/>
    <graphics/>
  </devices>
</domain>

• binary translation
• replace non-virtualizable instructions with trap
• whenever a privileged instruction is executed => trap & emulate

• Hypervisor exposes a set of APIs to guest OS
• Requires changes in guest OS

• eliminate need for CPU paravirtualization
• Intel VT-x (vmx) or AMD-V (svm)
• Enable in BIOS
• requirements for many hypervisors, e.g. KVM

• CONFIG_KVM{_INTEL,_AMD}
• QEMU to emulate I/O

<domain type='kvm'>
  <name>fedora</name>
  <uuid>63840878-0deb-4095-97e6-fc444d9bc9fa</uuid>
  ...
</domain>

• Don't emulate HW, just directly pass data between domain and hypervisor
• Defines set of APIs
• Requires guest OS drivers: Linux >= 2.6.25, Windows >= Vista
• Host drivers in hypervisor

<domain type='kvm'>
  <name>fedora</name>
  <uuid>63840878-0deb-4095-97e6-fc444d9bc9fa</uuid>
  <devices>
    <disk type='file' device='disk'>
      <target dev='vda' bus='virtio'/>
    </disk>
    <interface type='network'>
      <model type='virtio'/>
    </interface>
    <memballoon model='virtio'/>
  </devices>
</domain>

• Emulate real GPU with the help of the host GPU
• Pass OpenGL® commands from guest onto host GPU
• Use virglrenderer to render on the host GPU

• What the format of domain configuration?
  • XML
• How do you enable HW assisted virtualization?
  • BIOS, KVM module, <domain type='kvm'/>
• How do you enable VIRTIO?
  • Pass correct value to model, type, bus, etc. attributes

• Resource limitation, accounting, isolation
• Can be used for prioritization
• Set of controller groups: cpuset, blkio, memory, etc.
• Forms a hierarchical tree, PIDs placed anywhere / into leaves

• Completely Fair Scheduling, O(log N)
• Overhead, jitter

• vCPU pinning
• memory pinning
• emulator pinning

<domain type='kvm'>
  <name>fedora</name>
  <vcpu placement='static'>4</vcpu>
  <numatune>
    <memory mode='strict' nodeset='0-3'/>
    <memnode cellid='0' mode='strict' nodeset='0'/>
  </numatune>
  <cputune>
    <vcpupin vcpu="0" cpuset="1-4,^2"/>
    <emulatorpin cpuset="1-3"/>
    <iothreadpin iothread="1" cpuset="5,6"/>
  </cputune>
</domain>

• Multiple layers of cache: guest OS, QEMU, host OS
• If possible, trust host and avoid caching in QEMU

<disk type='file' device='disk'>
  <driver name='qemu' type='qcow2' cache='none' io='native'/>
  <source file='/path/to/my_disk.qcow2'/>
  <target dev='vda' bus='virtio'/>
</disk>

Visit talk Qemu Disk I/O: Which performs better, Native or Threads?

• I/O schedulers
• prealloc storage
• pass partition

• Bare metal performance
• Not shared

• Able to create multiple VF on the fly
• Share PCI device

<interface type='hostdev' managed='yes'>
  <mac address='52:54:00:6d:90:02'/>
  <source>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
  </source>
</interface>

• Giving more resources than have
• KSM, <nosharepages/>

• Tool living in libvirt repository

# virt-host-validate
  QEMU: Checking for hardware virtualization              : PASS
  QEMU: Checking if device /dev/kvm exists                : PASS
  ...
  QEMU: Checking for device assignment IOMMU support      : PASS
  QEMU: Checking if IOMMU is enabled by kernel            : PASS
   LXC: Checking for Linux >= 2.6.26                      : PASS
   LXC: Checking for namespace ipc                        : PASS
   LXC: Checking for namespace mnt                        : PASS
  ...

• http://libvirt.org/formatdomain.html
• Red Hat Enterprise Linux Virtualization tuning
• libvirt-users@redhat.com

• Use HW assisted virtualization
• Select virtio
• Pin