mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-07-06 18:05:45 +00:00
486a86eb18
Describe the new cgroups layout, how to customize placement of guests and what virsh commands are used to access the parameters. Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
286 lines
9.2 KiB
XML
286 lines
9.2 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|
<body>
|
|
<h1>Control Groups Resource Management</h1>
|
|
|
|
<ul id="toc"></ul>
|
|
|
|
<p>
|
|
The QEMU and LXC drivers make use of the Linux "Control Groups" facility
|
|
for applying resource management to their virtual machines and containers.
|
|
</p>
|
|
|
|
<h2><a name="requiredControllers">Required controllers</a></h2>
|
|
|
|
<p>
|
|
The control groups filesystem supports multiple "controllers". By default
|
|
the init system (such as systemd) should mount all controllers compiled
|
|
into the kernel at <code>/sys/fs/cgroup/$CONTROLLER-NAME</code>. Libvirt
|
|
will never attempt to mount any controllers itself, merely detect where
|
|
they are mounted.
|
|
</p>
|
|
|
|
<p>
|
|
The QEMU driver is capable of using the <code>cpuset</code>,
|
|
<code>cpu</code>, <code>memory</code>, <code>blkio</code> and
|
|
<code>devices</code> controllers. None of them are compulsory.
|
|
If any controller is not mounted, the resource management APIs
|
|
which use it will cease to operate. It is possible to explicitly
|
|
turn off use of a controller, even when mounted, via the
|
|
<code>/etc/libvirt/qemu.conf</code> configuration file.
|
|
</p>
|
|
|
|
<p>
|
|
The LXC driver is capable of using the <code>cpuset</code>,
|
|
<code>cpu</code>, <code>cpuset</code>, <code>freezer</code>,
|
|
<code>memory</code>, <code>blkio</code> and <code>devices</code>
|
|
controllers. The <code>cpuset</code>, <code>devices</code>
|
|
and <code>memory</code> controllers are compulsory. Without
|
|
them mounted, no containers can be started. If any of the
|
|
other controllers are not mounted, the resource management APIs
|
|
which use them will cease to operate.
|
|
</p>
|
|
|
|
<h2><a name="currentLayout">Current cgroups layout</a></h2>
|
|
|
|
<p>
|
|
As of libvirt 1.0.5 or later, the cgroups layout created by libvirt has been
|
|
simplified, in order to facilitate the setup of resource control policies by
|
|
administrators / management applications. The layout is based on the concepts of
|
|
"partitions" and "consumers". Each virtual machine or container is a consumer,
|
|
and has a corresponding cgroup named <code>$VMNAME.libvirt-{qemu,lxc}</code>.
|
|
Each consumer is associated with exactly one partition, which also have a
|
|
corresponding cgroup usually named <code>$PARTNAME.partition</code>. The
|
|
exceptions to this naming rule are the three top level default partitions,
|
|
named <code>/system</code> (for system services), <code>/user</code> (for
|
|
user login sessions) and <code>/machine</code> (for virtual machines and
|
|
containers). By default every consumer will of course be associated with
|
|
the <code>/machine</code> partition. This leads to a hierarchy that looks
|
|
like
|
|
</p>
|
|
|
|
<pre>
|
|
$ROOT
|
|
|
|
|
+- system
|
|
| |
|
|
| +- libvirtd.service
|
|
|
|
|
+- machine
|
|
|
|
|
+- vm1.libvirt-qemu
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- vm2.libvirt-qemu
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- vm3.libvirt-qemu
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- container1.libvirt-lxc
|
|
|
|
|
+- container2.libvirt-lxc
|
|
|
|
|
+- container3.libvirt-lxc
|
|
</pre>
|
|
|
|
<p>
|
|
The default cgroups layout ensures that, when there is contention for
|
|
CPU time, it is shared equally between system services, user sessions
|
|
and virtual machines / containers. This prevents virtual machines from
|
|
locking the administrator out of the host, or impacting execution of
|
|
system services. Conversely, when there is no contention from
|
|
system services / user sessions, it is possible for virtual machines
|
|
to fully utilize the host CPUs.
|
|
</p>
|
|
|
|
<h2><a name="customPartiton">Using custom partitions</a></h2>
|
|
|
|
<p>
|
|
If there is a need to apply resource constraints to groups of
|
|
virtual machines or containers, then the single default
|
|
partition <code>/machine</code> may not be sufficiently
|
|
flexible. The administrator may wish to sub-divide the
|
|
default partition, for example into "testing" and "production"
|
|
partitions, and then assign each guest to a specific
|
|
sub-partition. This is achieved via a small element addition
|
|
to the guest domain XML config, just below the main <code>domain</code>
|
|
element
|
|
</p>
|
|
|
|
<pre>
|
|
...
|
|
<resource>
|
|
<partition>/machine/production</partition>
|
|
</resource>
|
|
...
|
|
</pre>
|
|
|
|
<p>
|
|
Libvirt will not auto-create the cgroups directory to back
|
|
this partition. In the future, libvirt / virsh will provide
|
|
APIs / commands to create custom partitions, but currently
|
|
this is left as an exercise for the administrator. For
|
|
example, given the XML config above, the admin would need
|
|
to create a cgroup named '/machine/production.partition'
|
|
</p>
|
|
|
|
<pre>
|
|
# cd /sys/fs/cgroup
|
|
# for i in blkio cpu,cpuacct cpuset devices freezer memory net_cls perf_event
|
|
do
|
|
mkdir $i/machine/production.partition
|
|
done
|
|
# for i in cpuset.cpus cpuset.mems
|
|
do
|
|
cat cpuset/machine/$i > cpuset/machine/production.partition/$i
|
|
done
|
|
</pre>
|
|
|
|
<p>
|
|
<strong>Note:</strong> the cgroups directory created as a ".partition"
|
|
suffix, but the XML config does not require this suffix.
|
|
</p>
|
|
|
|
<p>
|
|
<strong>Note:</strong> the ability to place guests in custom
|
|
partitions is only available with libvirt >= 1.0.5, using
|
|
the new cgroup layout. The legacy cgroups layout described
|
|
later did not support customization per guest.
|
|
</p>
|
|
|
|
<h2><a name="resourceAPIs">Resource management APIs/commands</a></h2>
|
|
|
|
<p>
|
|
Since libvirt aims to provide an API which is portable across
|
|
hypervisors, the concept of cgroups is not exposed directly
|
|
in the API or XML configuration. It is considered to be an
|
|
internal implementation detail. Instead libvirt provides a
|
|
set of APIs for applying resource controls, which are then
|
|
mapped to corresponding cgroup tunables
|
|
</p>
|
|
|
|
<h3>Scheduler tuning</h3>
|
|
|
|
<p>
|
|
Parameters from the "cpu" controller are exposed via the
|
|
<code>schedinfo</code> command in virsh.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh schedinfo demo
|
|
Scheduler : posix
|
|
cpu_shares : 1024
|
|
vcpu_period : 100000
|
|
vcpu_quota : -1
|
|
emulator_period: 100000
|
|
emulator_quota : -1</pre>
|
|
|
|
|
|
<h3>Block I/O tuning</h3>
|
|
|
|
<p>
|
|
Parameters from the "blkio" controller are exposed via the
|
|
<code>bkliotune</code> command in virsh.
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
# virsh blkiotune demo
|
|
weight : 500
|
|
device_weight : </pre>
|
|
|
|
<h3>Memory tuning</h3>
|
|
|
|
<p>
|
|
Parameters from the "memory" controller are exposed via the
|
|
<code>memtune</code> command in virsh.
|
|
</p>
|
|
|
|
<pre>
|
|
# virsh memtune demo
|
|
hard_limit : 580192
|
|
soft_limit : unlimited
|
|
swap_hard_limit: unlimited
|
|
</pre>
|
|
|
|
<h3>Network tuning</h3>
|
|
|
|
<p>
|
|
The <code>net_cls</code> is not currently used. Instead traffic
|
|
filter policies are set directly against individual virtual
|
|
network interfaces.
|
|
</p>
|
|
|
|
<h2><a name="legacyLayout">Legacy cgroups layout</a></h2>
|
|
|
|
<p>
|
|
Prior to libvirt 1.0.5, the cgroups layout created by libvirt was different
|
|
from that described above, and did not allow for administrator customization.
|
|
Libvirt used a fixed, 3-level hierarchy <code>libvirt/{qemu,lxc}/$VMNAME</code>
|
|
which was rooted at the point in the hierarchy where libvirtd itself was
|
|
located. So if libvirtd was placed at <code>/system/libvirtd.service</code>
|
|
by systemd, the groups for each virtual machine / container would be located
|
|
at <code>/system/libvirtd.service/libvirt/{qemu,lxc}/$VMNAME</code>. In addition
|
|
to this, the QEMU drivers further child groups for each vCPU thread and the
|
|
emulator thread(s). This leads to a hierarchy that looked like
|
|
</p>
|
|
|
|
|
|
<pre>
|
|
$ROOT
|
|
|
|
|
+- system
|
|
|
|
|
+- libvirtd.service
|
|
|
|
|
+- libvirt
|
|
|
|
|
+- qemu
|
|
| |
|
|
| +- vm1
|
|
| | |
|
|
| | +- emulator
|
|
| | +- vcpu0
|
|
| | +- vcpu1
|
|
| |
|
|
| +- vm2
|
|
| | |
|
|
| | +- emulator
|
|
| | +- vcpu0
|
|
| | +- vcpu1
|
|
| |
|
|
| +- vm3
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- lxc
|
|
|
|
|
+- container1
|
|
|
|
|
+- container2
|
|
|
|
|
+- container3
|
|
</pre>
|
|
|
|
<p>
|
|
Although current releases are much improved, historically the use of deep
|
|
hierarchies has had a significant negative impact on the kernel scalability.
|
|
The legacy libvirt cgroups layout highlighted these problems, to the detriment
|
|
of the performance of virtual machines and containers.
|
|
</p>
|
|
</body>
|
|
</html>
|