[libvirt] [PATCH] Add docs about cgroups layout and usage
From: "Daniel P. Berrange" <berrange@redhat.com> 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> --- docs/cgroups.html.in | 285 +++++++++++++++++++++++++++++++++++++++++++++++++++ docs/sitemap.html.in | 4 + 2 files changed, 289 insertions(+) create mode 100644 docs/cgroups.html.in diff --git a/docs/cgroups.html.in b/docs/cgroups.html.in new file mode 100644 index 0000000..3be0672 --- /dev/null +++ b/docs/cgroups.html.in @@ -0,0 +1,285 @@ +<?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 & 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. ConverselyWhen 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 hiearchy <code>libvirt/{qemu,lxc}/$VMNAME</code> + which was rooted at the point in the hiearchy 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}/$VMNAME</code>. In addition + to this, the QEMU drivers further child groups for each vCPU thread and the + emulator thread(s). This leads to a hiearchy that looked like + </p> + + + <pre> +$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 + hiearchies 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> diff --git a/docs/sitemap.html.in b/docs/sitemap.html.in index 619e4a1..cb7cc5b 100644 --- a/docs/sitemap.html.in +++ b/docs/sitemap.html.in @@ -89,6 +89,10 @@ <span>Ensuring exclusive guest access to disks</span> </li> <li> + <a href="cgroups.html">CGroups</a> + <span>Control groups integration</span> + </li> + <li> <a href="hooks.html">Hooks</a> <span>Hooks for system specific management</span> </li> -- 1.8.1.4
On 05/03/2013 10:49 AM, Daniel P. Berrange wrote:
From: "Daniel P. Berrange" <berrange@redhat.com>
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> --- docs/cgroups.html.in | 285 +++++++++++++++++++++++++++++++++++++++++++++++++++ docs/sitemap.html.in | 4 + 2 files changed, 289 insertions(+) create mode 100644 docs/cgroups.html.in
+ + <p> + The QEMU and LXC drivers make use of the Linux "Control Groups" facility + for applying resource management to their virtual machines & containers.
s/&/and/ - '&' looks too informal.
+ + <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. ConverselyWhen there is no contention from
s/ConverselyWhen/Conversely, when/
+ <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
Yay - I already know that I will be pointing people to this page on IRC.
+ </p> + + <h3>Scheduler tuning</h3> + + <p> + Parameters from the "cpu" controller are exposed via the + <code>schedinfo</code> command in virsh.
I think it is also worth mentioning which portions of the XML hold the information (a link to right section of formatdomain.html) and which APIs are being used, rather than just saying virsh exposes it. But that can be a followup patch - getting this out there now and improving it later is acceptable, since anything is better than the current lack of docs.
+ + <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 hiearchy <code>libvirt/{qemu,lxc}/$VMNAME</code>
s/hiearchy/hierarchy/
+ which was rooted at the point in the hiearchy where libvirtd itself was
and again
+ located. So if libvirtd was placed at <code>/system/libvirtd.service</code> + by systemd, the groups for each virtual machine / container would be located + at <code>/system/libvirtd.service/libvirt/{qemu,lxc}/$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 hiearchy that looked like
and again
+ <p> + Although current releases are much improved, historically the use of deep + hiearchies has had a significant negative impact on the kernel scalability.
and again. ACK with typos fixed. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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