mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-11-03 20:01:16 +00:00
42b5e496a7
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Erik Skultety <eskultet@redhat.com>
365 lines
12 KiB
ReStructuredText
365 lines
12 KiB
ReStructuredText
==================================
|
|
Control Groups Resource Management
|
|
==================================
|
|
|
|
.. contents::
|
|
|
|
The QEMU and LXC drivers make use of the Linux "Control Groups" facility for
|
|
applying resource management to their virtual machines and containers.
|
|
|
|
Required controllers
|
|
--------------------
|
|
|
|
The control groups filesystem supports multiple "controllers". By default the
|
|
init system (such as systemd) should mount all controllers compiled into the
|
|
kernel at ``/sys/fs/cgroup/$CONTROLLER-NAME``. Libvirt will never attempt to
|
|
mount any controllers itself, merely detect where they are mounted.
|
|
|
|
The QEMU driver is capable of using the ``cpuset``, ``cpu``, ``cpuacct``,
|
|
``memory``, ``blkio`` and ``devices`` 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 ``/etc/libvirt/qemu.conf`` configuration file.
|
|
|
|
The LXC driver is capable of using the ``cpuset``, ``cpu``, ``cpuacct``,
|
|
``freezer``, ``memory``, ``blkio`` and ``devices`` controllers. The ``cpuacct``,
|
|
``devices`` and ``memory`` 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.
|
|
|
|
Current cgroups layout
|
|
----------------------
|
|
|
|
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 new layout is based on the
|
|
concepts of "partitions" and "consumers". A "consumer" is a cgroup which holds
|
|
the processes for a single virtual machine or container. A "partition" is a
|
|
cgroup which does not contain any processes, but can have resource controls
|
|
applied. A "partition" will have zero or more child directories which may be
|
|
either "consumer" or "partition".
|
|
|
|
As of libvirt 1.1.1 or later, the cgroups layout will have some slight
|
|
differences when running on a host with systemd 205 or later. The overall tree
|
|
structure is the same, but there are some differences in the naming conventions
|
|
for the cgroup directories. Thus the following docs split in two, one describing
|
|
systemd hosts and the other non-systemd hosts.
|
|
|
|
Systemd cgroups integration
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
On hosts which use systemd, each consumer maps to a systemd scope unit, while
|
|
partitions map to a system slice unit.
|
|
|
|
Systemd scope naming
|
|
^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The systemd convention is for the scope name of virtual machines / containers to
|
|
be of the general format ``machine-$NAME.scope``. Libvirt forms the ``$NAME``
|
|
part of this by concatenating the driver type with the id and truncated name of
|
|
the guest, and then escaping any systemd reserved characters. So for a guest
|
|
``demo`` running under the ``lxc`` driver, we get a ``$NAME`` of
|
|
``lxc-12345-demo`` which when escaped is ``lxc\x2d12345\x2ddemo``. So the
|
|
complete scope name is ``machine-lxc\x2d12345\x2ddemo.scope``. The scope names
|
|
map directly to the cgroup directory names.
|
|
|
|
Systemd slice naming
|
|
^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The systemd convention for slice naming is that a slice should include the name
|
|
of all of its parents prepended on its own name. So for a libvirt partition
|
|
``/machine/engineering/testing``, the slice name will be
|
|
``machine-engineering-testing.slice``. Again the slice names map directly to the
|
|
cgroup directory names. Systemd creates three top level slices by default,
|
|
``system.slice`` ``user.slice`` and ``machine.slice``. All virtual machines or
|
|
containers created by libvirt will be associated with ``machine.slice`` by
|
|
default.
|
|
|
|
Systemd cgroup layout
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Given this, a possible systemd cgroups layout involving 3 qemu guests, 3 lxc
|
|
containers and 3 custom child slices, would be:
|
|
|
|
::
|
|
|
|
$ROOT
|
|
|
|
|
+- system.slice
|
|
| |
|
|
| +- libvirtd.service
|
|
|
|
|
+- machine.slice
|
|
|
|
|
+- machine-qemu\x2d1\x2dvm1.scope
|
|
| |
|
|
| +- libvirt
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- machine-qemu\x2d2\x2dvm2.scope
|
|
| |
|
|
| +- libvirt
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- machine-qemu\x2d3\x2dvm3.scope
|
|
| |
|
|
| +- libvirt
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- machine-engineering.slice
|
|
| |
|
|
| +- machine-engineering-testing.slice
|
|
| | |
|
|
| | +- machine-lxc\x2d11111\x2dcontainer1.scope
|
|
| |
|
|
| +- machine-engineering-production.slice
|
|
| |
|
|
| +- machine-lxc\x2d22222\x2dcontainer2.scope
|
|
|
|
|
+- machine-marketing.slice
|
|
|
|
|
+- machine-lxc\x2d33333\x2dcontainer3.scope
|
|
|
|
Prior libvirt 7.1.0 the topology doesn't have extra ``libvirt`` directory.
|
|
|
|
Non-systemd cgroups layout
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
On hosts which do not use systemd, each consumer has a corresponding cgroup
|
|
named ``$VMNAME.libvirt-{qemu,lxc}``. Each consumer is associated with exactly
|
|
one partition, which also have a corresponding cgroup usually named
|
|
``$PARTNAME.partition``. The exceptions to this naming rule is the top level
|
|
default partition for virtual machines and containers ``/machine``.
|
|
|
|
Given this, a possible non-systemd cgroups layout involving 3 qemu guests, 3 lxc
|
|
containers and 2 custom child slices, would be:
|
|
|
|
::
|
|
|
|
$ROOT
|
|
|
|
|
+- machine
|
|
|
|
|
+- qemu-1-vm1.libvirt-qemu
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- qeme-2-vm2.libvirt-qemu
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- qemu-3-vm3.libvirt-qemu
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- engineering.partition
|
|
| |
|
|
| +- testing.partition
|
|
| | |
|
|
| | +- lxc-11111-container1.libvirt-lxc
|
|
| |
|
|
| +- production.partition
|
|
| |
|
|
| +- lxc-22222-container2.libvirt-lxc
|
|
|
|
|
+- marketing.partition
|
|
|
|
|
+- lxc-33333-container3.libvirt-lxc
|
|
|
|
Using custom partitions
|
|
-----------------------
|
|
|
|
If there is a need to apply resource constraints to groups of virtual machines
|
|
or containers, then the single default partition ``/machine`` 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 ``domain``
|
|
element
|
|
|
|
::
|
|
|
|
...
|
|
<resource>
|
|
<partition>/machine/production</partition>
|
|
</resource>
|
|
...
|
|
|
|
Note that the partition names in the guest XML are using a generic naming
|
|
format, not the low level naming convention required by the underlying host OS.
|
|
That is, you should not include any of the ``.partition`` or ``.slice`` suffixes
|
|
in the XML config. Given a partition name ``/machine/production``, libvirt will
|
|
automatically apply the platform specific translation required to get
|
|
``/machine/production.partition`` (non-systemd) or
|
|
``/machine.slice/machine-production.slice`` (systemd) as the underlying cgroup
|
|
name
|
|
|
|
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.
|
|
|
|
**Note:** 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 in this document did not support customization per guest.
|
|
|
|
Creating custom partitions (systemd)
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Given the XML config above, the admin on a systemd based host would need to
|
|
create a unit file ``/etc/systemd/system/machine-production.slice``
|
|
|
|
::
|
|
|
|
# cat > /etc/systemd/system/machine-testing.slice <<EOF
|
|
[Unit]
|
|
Description=VM testing slice
|
|
Before=slices.target
|
|
Wants=machine.slice
|
|
EOF
|
|
# systemctl start machine-testing.slice
|
|
|
|
Creating custom partitions (non-systemd)
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Given the XML config above, the admin on a non-systemd based host would need to
|
|
create a cgroup named '/machine/production.partition'
|
|
|
|
::
|
|
|
|
# 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/$i
|
|
done
|
|
|
|
Resource management APIs/commands
|
|
---------------------------------
|
|
|
|
Since libvirt aims to provide an API which is portable across hypervisors, the
|
|
concept of cgroups is not exposed directly in the API or XML configuration. It
|
|
is considered to be an internal implementation detail. Instead libvirt provides
|
|
a set of APIs for applying resource controls, which are then mapped to
|
|
corresponding cgroup tunables
|
|
|
|
Scheduler tuning
|
|
~~~~~~~~~~~~~~~~
|
|
|
|
Parameters from the "cpu" controller are exposed via the ``schedinfo`` command
|
|
in virsh.
|
|
|
|
::
|
|
|
|
# virsh schedinfo demo
|
|
Scheduler : posix
|
|
cpu_shares : 1024
|
|
vcpu_period : 100000
|
|
vcpu_quota : -1
|
|
emulator_period: 100000
|
|
emulator_quota : -1
|
|
|
|
Block I/O tuning
|
|
~~~~~~~~~~~~~~~~
|
|
|
|
Parameters from the "blkio" controller are exposed via the ``bkliotune`` command
|
|
in virsh.
|
|
|
|
::
|
|
|
|
# virsh blkiotune demo
|
|
weight : 500
|
|
device_weight :
|
|
|
|
Memory tuning
|
|
~~~~~~~~~~~~~
|
|
|
|
Parameters from the "memory" controller are exposed via the ``memtune`` command
|
|
in virsh.
|
|
|
|
::
|
|
|
|
# virsh memtune demo
|
|
hard_limit : 580192
|
|
soft_limit : unlimited
|
|
swap_hard_limit: unlimited
|
|
|
|
Network tuning
|
|
~~~~~~~~~~~~~~
|
|
|
|
The ``net_cls`` is not currently used. Instead traffic filter policies are set
|
|
directly against individual virtual network interfaces.
|
|
|
|
Legacy cgroups layout
|
|
---------------------
|
|
|
|
Prior to libvirt 1.0.5, the cgroups layout created by libvirt was different from
|
|
that described above, and did not allow for administrator customization. Libvirt
|
|
used a fixed, 3-level hierarchy ``libvirt/{qemu,lxc}/$VMNAME`` which was rooted
|
|
at the point in the hierarchy where libvirtd itself was located. So if libvirtd
|
|
was placed at ``/system/libvirtd.service`` by systemd, the groups for each
|
|
virtual machine / container would be located at
|
|
``/system/libvirtd.service/libvirt/{qemu,lxc}/$VMNAME``. 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
|
|
|
|
::
|
|
|
|
$ROOT
|
|
|
|
|
+- system
|
|
|
|
|
+- libvirtd.service
|
|
|
|
|
+- libvirt
|
|
|
|
|
+- qemu
|
|
| |
|
|
| +- vm1
|
|
| | |
|
|
| | +- emulator
|
|
| | +- vcpu0
|
|
| | +- vcpu1
|
|
| |
|
|
| +- vm2
|
|
| | |
|
|
| | +- emulator
|
|
| | +- vcpu0
|
|
| | +- vcpu1
|
|
| |
|
|
| +- vm3
|
|
| |
|
|
| +- emulator
|
|
| +- vcpu0
|
|
| +- vcpu1
|
|
|
|
|
+- lxc
|
|
|
|
|
+- container1
|
|
|
|
|
+- container2
|
|
|
|
|
+- container3
|
|
|
|
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.
|