![Tom Fifield](/assets/img/avatar_default.png)
A standard pre-release patch, looking for any obsolete text to remove, and references to newly unsupported releases to remove. Feel free to update the patch if you find other things. Review request: this patch touches many files in a small way. Please try and focus on the small changes, and not the rest of the file ... since many of them do need an edit ;) Change-Id: I383c51acf149bb6553ddfd33cad382f5dd15fe62
172 lines
10 KiB
XML
172 lines
10 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<section xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" xml:id="kvm">
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<?dbhtml stop-chunking?>
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<title>KVM</title>
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<para>KVM is configured as the default hypervisor for Compute.</para>
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<note>
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<para>This document contains several sections about hypervisor selection. If you are reading
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this document linearly, you do not want to load the KVM module before you install
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<systemitem class="service">nova-compute</systemitem>. The <systemitem
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class="service">nova-compute</systemitem> service depends on qemu-kvm, which
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installs <filename>/lib/udev/rules.d/45-qemu-kvm.rules</filename>, which sets the
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correct permissions on the /dev/kvm device node.</para>
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</note>
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<para>To enable KVM explicitly, add the following configuration options to the
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<filename>/etc/nova/nova.conf</filename> file:</para>
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<programlisting language="ini">compute_driver=libvirt.LibvirtDriver
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libvirt_type=kvm</programlisting>
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<para>The KVM hypervisor supports the following virtual machine image formats:</para>
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<itemizedlist>
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<listitem>
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<para>Raw</para>
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</listitem>
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<listitem>
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<para>QEMU Copy-on-write (qcow2)</para>
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</listitem>
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<listitem>
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<para>QED Qemu Enhanced Disk</para>
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</listitem>
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<listitem>
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<para>VMWare virtual machine disk format (vmdk)</para>
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</listitem>
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</itemizedlist>
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<para>This section describes how to enable KVM on your system. For more information, see the
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following distribution-specific documentation:</para>
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<itemizedlist>
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<listitem>
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<para><link
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xlink:href="http://fedoraproject.org/wiki/Getting_started_with_virtualization"
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>Fedora: Getting started with virtualization</link> from the Fedora project
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wiki.</para>
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</listitem>
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<listitem>
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<para><link xlink:href="https://help.ubuntu.com/community/KVM/Installation">Ubuntu:
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KVM/Installation</link> from the Community Ubuntu documentation.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://static.debian-handbook.info/browse/stable/sect.virtualization.html#idp11279352"
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>Debian: Virtualization with KVM</link> from the Debian handbook.</para>
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</listitem>
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<listitem>
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<para><link
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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"
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>Red Hat Enterprise Linux: Installing virtualization packages on an existing Red
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Hat Enterprise Linux system</link> from the <citetitle>Red Hat Enterprise Linux
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Virtualization Host Configuration and Guest Installation
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Guide</citetitle>.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://doc.opensuse.org/documentation/html/openSUSE/opensuse-kvm/cha.kvm.requires.html#sec.kvm.requires.install"
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>openSUSE: Installing KVM</link> from the openSUSE Virtualization with KVM
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manual.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://doc.opensuse.org/products/draft/SLES/SLES-kvm_sd_draft/cha.kvm.requires.html#sec.kvm.requires.install"
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>SLES: Installing KVM</link> from the SUSE Linux Enterprise Server
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Virtualization with KVM manual.</para>
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</listitem>
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</itemizedlist>
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<xi:include href="../../common/section_kvm_enable.xml"/>
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<section xml:id="libvirt-xml-cpu-model">
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<title>Specify the CPU model of KVM guests</title>
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<para>The Compute service enables you to control the guest CPU model that is exposed to KVM
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virtual machines. Use cases include:</para>
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<itemizedlist>
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<listitem>
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<para>To maximize performance of virtual machines by exposing new host CPU features
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to the guest</para>
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</listitem>
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<listitem>
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<para>To ensure a consistent default CPU across all machines, removing reliance of
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variable QEMU defaults</para>
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</listitem>
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</itemizedlist>
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<para>In libvirt, the CPU is specified by providing a base CPU model name (which is a
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shorthand for a set of feature flags), a set of additional feature flags, and the
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topology (sockets/cores/threads). The libvirt KVM driver provides a number of standard
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CPU model names. These models are defined in the
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<filename>/usr/share/libvirt/cpu_map.xml</filename> file. Check this file to
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determine which models are supported by your local installation.</para>
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<para>Two Compute configuration options define which type of CPU model is exposed to the
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hypervisor when using KVM: <literal>libvirt_cpu_mode</literal> and
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<literal>libvirt_cpu_model</literal>.</para>
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<para>The <literal>libvirt_cpu_mode</literal> option can take one of the following values:
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<literal>none</literal>, <literal>host-passthrough</literal>,
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<literal>host-model</literal>, and <literal>custom</literal>.</para>
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<simplesect>
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<title>Host model (default for KVM & QEMU)</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=host-model</literal>, libvirt identifies the CPU model
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in <filename>/usr/share/libvirt/cpu_map.xml</filename> file that most closely
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matches the host, and requests additional CPU flags to complete the match. This
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configuration provides the maximum functionality and performance and maintains good
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reliability and compatibility if the guest is migrated to another host with slightly
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different host CPUs.</para>
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</simplesect>
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<simplesect>
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<title>Host pass through</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=host-passthrough</literal>, libvirt tells KVM to pass
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through the host CPU with no modifications. The difference to host-model, instead of
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just matching feature flags, every last detail of the host CPU is matched. This
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gives absolutely best performance, and can be important to some apps which check low
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level CPU details, but it comes at a cost with respect to migration: the guest can
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only be migrated to an exactly matching host CPU.</para>
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</simplesect>
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<simplesect>
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<title>Custom</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=custom</literal>, you can explicitly specify one of
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the supported named model using the libvirt_cpu_model configuration option. For
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example, to configure the KVM guests to expose Nehalem CPUs, your
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<filename>nova.conf</filename> file should contain:</para>
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<programlisting language="ini">libvirt_cpu_mode=custom
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libvirt_cpu_model=Nehalem</programlisting>
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</simplesect>
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<simplesect>
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<title>None (default for all libvirt-driven hypervisors other than KVM &
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QEMU)</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=none</literal>, libvirt does not specify a CPU model.
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Instead, the hypervisor chooses the default model.</para>
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</simplesect>
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</section>
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<section xml:id="kvm-guest-agent-support">
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<title>Guest agent support</title>
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<para>Use guest agents to enable optional access between compute nodes and guests through a
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socket, using the QMP protocol.</para>
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<para>To enable this feature, you must set <literal>hw_qemu_guest_agent=yes</literal> as a
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metadata parameter on the image you wish to use to create guest-agent-capable instances
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from. You can explicitly disable the feature by setting
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<literal>hw_qemu_guest_agent=no</literal> in the image metadata.</para>
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</section>
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<section xml:id="kvm-performance">
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<title>KVM performance tweaks</title>
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<para>The <link xlink:href="http://www.linux-kvm.org/page/VhostNet">VHostNet</link> kernel
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module improves network performance. To load the kernel module, run the following
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command as root:</para>
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<screen><prompt>#</prompt> <userinput>modprobe vhost_net</userinput></screen>
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</section>
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<section xml:id="kvm-troubleshooting">
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<title>Troubleshoot KVM</title>
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<para>Trying to launch a new virtual machine instance fails with the
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<literal>ERROR</literal>state, and the following error appears in the
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<filename>/var/log/nova/nova-compute.log</filename> file:</para>
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<screen><computeroutput>libvirtError: internal error no supported architecture for os type 'hvm'</computeroutput></screen>
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<para>This message indicates that the KVM kernel modules were not loaded.</para>
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<para>If you cannot start VMs after installation without rebooting, the permissions might
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not be correct. This can happen if you load the KVM module before you install
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<systemitem class="service">nova-compute</systemitem>. To check whether the group is
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set to <systemitem>kvm</systemitem>, run:</para>
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<screen><prompt>#</prompt> <userinput>ls -l /dev/kvm</userinput></screen>
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<para>If it is not set to <systemitem>kvm</systemitem>, run:</para>
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<screen><prompt>#</prompt> <userinput>udevadm trigger</userinput></screen>
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</section>
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</section>
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