openstack-manuals/doc/config-reference/compute/section_hypervisor_kvm.xml
Andreas Jaeger 4418c9962a Remove sudo usage from config reference
Remove sudo usage and adjust prompts as needed.

Change-Id: Ia1df06230203f7c8393b7f369c3dc396d8143799
2014-03-10 20:12:45 +01:00

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" xml:id="kvm">
<?dbhtml stop-chunking?>
<title>KVM</title>
<para>KVM is configured as the default hypervisor for Compute.</para>
<note>
<para>This document contains several sections about hypervisor selection. If you are reading
this document linearly, you do not want to load the KVM module before you install
<systemitem class="service">nova-compute</systemitem>. The <systemitem
class="service">nova-compute</systemitem> service depends on qemu-kvm, which
installs <filename>/lib/udev/rules.d/45-qemu-kvm.rules</filename>, which sets the
correct permissions on the /dev/kvm device node.</para>
</note>
<para>To enable KVM explicitly, add the following configuration options to the
<filename>/etc/nova/nova.conf</filename> file:</para>
<programlisting language="ini">compute_driver=libvirt.LibvirtDriver
libvirt_type=kvm</programlisting>
<para>The KVM hypervisor supports the following virtual machine image formats:</para>
<itemizedlist>
<listitem>
<para>Raw</para>
</listitem>
<listitem>
<para>QEMU Copy-on-write (qcow2)</para>
</listitem>
<listitem>
<para>QED Qemu Enhanced Disk</para>
</listitem>
<listitem>
<para>VMWare virtual machine disk format (vmdk)</para>
</listitem>
</itemizedlist>
<para>This section describes how to enable KVM on your system. For more information, see the
following distribution-specific documentation:</para>
<itemizedlist>
<listitem>
<para><link
xlink:href="http://fedoraproject.org/wiki/Getting_started_with_virtualization"
>Fedora: Getting started with virtualization</link> from the Fedora project
wiki.</para>
</listitem>
<listitem>
<para><link xlink:href="https://help.ubuntu.com/community/KVM/Installation">Ubuntu:
KVM/Installation</link> from the Community Ubuntu documentation.</para>
</listitem>
<listitem>
<para><link
xlink:href="http://static.debian-handbook.info/browse/stable/sect.virtualization.html#idp11279352"
>Debian: Virtualization with KVM</link> from the Debian handbook.</para>
</listitem>
<listitem>
<para><link
xlink:href="http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/sect-Virtualization_Host_Configuration_and_Guest_Installation_Guide-Host_Installation-Installing_KVM_packages_on_an_existing_Red_Hat_Enterprise_Linux_system.html"
>Red Hat Enterprise Linux: Installing virtualization packages on an existing Red
Hat Enterprise Linux system</link> from the <citetitle>Red Hat Enterprise Linux
Virtualization Host Configuration and Guest Installation
Guide</citetitle>.</para>
</listitem>
<listitem>
<para><link
xlink:href="http://doc.opensuse.org/documentation/html/openSUSE/opensuse-kvm/cha.kvm.requires.html#sec.kvm.requires.install"
>openSUSE: Installing KVM</link> from the openSUSE Virtualization with KVM
manual.</para>
</listitem>
<listitem>
<para><link
xlink:href="http://doc.opensuse.org/products/draft/SLES/SLES-kvm_sd_draft/cha.kvm.requires.html#sec.kvm.requires.install"
>SLES: Installing KVM</link> from the SUSE Linux Enterprise Server
Virtualization with KVM manual.</para>
</listitem>
</itemizedlist>
<xi:include href="../../common/section_kvm_enable.xml"/>
<section xml:id="libvirt-xml-cpu-model">
<title>Specify the CPU model of KVM guests</title>
<para>The Compute service enables you to control the guest CPU model that is exposed to KVM
virtual machines. Use cases include:</para>
<itemizedlist>
<listitem>
<para>To maximize performance of virtual machines by exposing new host CPU features
to the guest</para>
</listitem>
<listitem>
<para>To ensure a consistent default CPU across all machines, removing reliance of
variable QEMU defaults</para>
</listitem>
</itemizedlist>
<para>In libvirt, the CPU is specified by providing a base CPU model name (which is a
shorthand for a set of feature flags), a set of additional feature flags, and the
topology (sockets/cores/threads). The libvirt KVM driver provides a number of standard
CPU model names. These models are defined in the
<filename>/usr/share/libvirt/cpu_map.xml</filename> file. Check this file to
determine which models are supported by your local installation.</para>
<para>Two Compute configuration options define which type of CPU model is exposed to the
hypervisor when using KVM: <literal>libvirt_cpu_mode</literal> and
<literal>libvirt_cpu_model</literal>.</para>
<para>The <literal>libvirt_cpu_mode</literal> option can take one of the following values:
<literal>none</literal>, <literal>host-passthrough</literal>,
<literal>host-model</literal>, and <literal>custom</literal>.</para>
<simplesect>
<title>Host model (default for KVM &amp; QEMU)</title>
<para>If your <filename>nova.conf</filename> file contains
<literal>libvirt_cpu_mode=host-model</literal>, libvirt identifies the CPU model
in <filename>/usr/share/libvirt/cpu_map.xml</filename> file that most closely
matches the host, and requests additional CPU flags to complete the match. This
configuration provides the maximum functionality and performance and maintains good
reliability and compatibility if the guest is migrated to another host with slightly
different host CPUs.</para>
</simplesect>
<simplesect>
<title>Host pass through</title>
<para>If your <filename>nova.conf</filename> file contains
<literal>libvirt_cpu_mode=host-passthrough</literal>, libvirt tells KVM to pass
through the host CPU with no modifications. The difference to host-model, instead of
just matching feature flags, every last detail of the host CPU is matched. This
gives absolutely best performance, and can be important to some apps which check low
level CPU details, but it comes at a cost with respect to migration: the guest can
only be migrated to an exactly matching host CPU.</para>
</simplesect>
<simplesect>
<title>Custom</title>
<para>If your <filename>nova.conf</filename> file contains
<literal>libvirt_cpu_mode=custom</literal>, you can explicitly specify one of
the supported named model using the libvirt_cpu_model configuration option. For
example, to configure the KVM guests to expose Nehalem CPUs, your
<filename>nova.conf</filename> file should contain:</para>
<programlisting language="ini">libvirt_cpu_mode=custom
libvirt_cpu_model=Nehalem</programlisting>
</simplesect>
<simplesect>
<title>None (default for all libvirt-driven hypervisors other than KVM &amp;
QEMU)</title>
<para>If your <filename>nova.conf</filename> file contains
<literal>libvirt_cpu_mode=none</literal>, libvirt does not specify a CPU model.
Instead, the hypervisor chooses the default model. This setting is equivalent to the
Compute service behavior prior to the Folsom release.</para>
</simplesect>
</section>
<section xml:id="kvm-guest-agent-support">
<title>Guest agent support</title>
<para>With the Havana release, support for guest agents was added, allowing optional access
between compute nods and guests through a socket, using the qmp protocol.</para>
<para>To enable this feature, you must set <literal>hw_qemu_guest_agent=yes</literal> as a
metadata parameter on the image you wish to use to create guest-agent-capable instances
from. You can explicitly disable the feature by setting
<literal>hw_qemu_guest_agent=no</literal> in the image metadata.</para>
</section>
<section xml:id="kvm-performance">
<title>KVM performance tweaks</title>
<para>The <link xlink:href="http://www.linux-kvm.org/page/VhostNet">VHostNet</link> kernel
module improves network performance. To load the kernel module, run the following
command as root:</para>
<screen><prompt>#</prompt> <userinput>modprobe vhost_net</userinput></screen>
</section>
<section xml:id="kvm-troubleshooting">
<title>Troubleshoot KVM</title>
<para>Trying to launch a new virtual machine instance fails with the
<literal>ERROR</literal>state, and the following error appears in the
<filename>/var/log/nova/nova-compute.log</filename> file:</para>
<screen><computeroutput>libvirtError: internal error no supported architecture for os type 'hvm'</computeroutput></screen>
<para>This message indicates that the KVM kernel modules were not loaded.</para>
<para>If you cannot start VMs after installation without rebooting, the permissions might
not be correct. This can happen if you load the KVM module before you install
<systemitem class="service">nova-compute</systemitem>. To check whether the group is
set to <systemitem>kvm</systemitem>, run:</para>
<screen><prompt>#</prompt> <userinput>ls -l /dev/kvm</userinput></screen>
<para>If it is not set to <systemitem>kvm</systemitem>, run:</para>
<screen><prompt>#</prompt> <userinput>udevadm trigger</userinput></screen>
</section>
</section>