
================================================
Testing NUMA related hardware setup with libvirt
================================================

This page describes how to test the libvirt driver's handling
of the NUMA placement, large page allocation and CPU pinning
features. It relies on setting up a virtual machine as the
test environment and requires support for nested virtualization
since plain QEMU is not sufficiently functional. The virtual
machine will itself be given NUMA topology, so it can then
act as a virtual "host" for testing purposes.

------------------------------------------
Provisioning a virtual machine for testing
------------------------------------------

The entire test process will take place inside a large virtual
machine running Fedora 21. The instructions should work for any
other Linux distribution which includes libvirt >= 1.2.9 and
QEMU >= 2.1.2

The tests will require support for nested KVM, which is not enabled
by default on hypervisor hosts. It must be explicitly turned on in
the host when loading the kvm-intel/kvm-amd kernel modules.

On Intel hosts verify it with

.. code-block:: bash

 # cat /sys/module/kvm_intel/parameters/nested
 N

 # rmmod kvm-intel
 # echo "options kvm-intel nested=y" > /etc/modprobe.d/dist.conf
 # modprobe kvm-intel

 # cat /sys/module/kvm_intel/parameters/nested
 Y

While on AMD hosts verify it with

.. code-block:: bash

 # cat /sys/module/kvm_amd/parameters/nested
 0

 # rmmod kvm-amd
 # echo "options kvm-amd nested=1" > /etc/modprobe.d/dist.conf
 # modprobe kvm-amd

 # cat /sys/module/kvm_amd/parameters/nested
 1

The virt-install command below shows how to provision a
basic Fedora 21 x86_64 guest with 8 virtual CPUs, 8 GB
of RAM and 20 GB of disk space:

.. code-block:: bash

 # cd /var/lib/libvirt/images
 # wget http://download.fedoraproject.org/pub/fedora/linux/releases/test/21-Alpha/Server/x86_64/iso/Fedora-Server-netinst-x86_64-21_Alpha.iso

 # virt-install \
    --name f21x86_64 \
    --ram 8000 \
    --vcpus 8 \
    --file /var/lib/libvirt/images/f21x86_64.img \
    --file-size 20
    --cdrom /var/lib/libvirt/images/Fedora-Server-netinst-x86_64-21_Alpha.iso \
    --os-variant fedora20

When the virt-viewer application displays the installer, follow
the defaults for the installation with a couple of exceptions

* The automatic disk partition setup can be optionally tweaked to
  reduce the swap space allocated. No more than 500MB is required,
  free'ing up an extra 1.5 GB for the root disk.

* Select "Minimal install" when asked for the installation type
  since a desktop environment is not required.

* When creating a user account be sure to select the option
  "Make this user administrator" so it gets 'sudo' rights

Once the installation process has completed, the virtual machine
will reboot into the final operating system. It is now ready to
deploy an OpenStack development environment.

---------------------------------
Setting up a devstack environment
---------------------------------

For later ease of use, copy your SSH public key into the virtual
machine

.. code-block:: bash

  # ssh-copy-id  <IP of VM>

Now login to the virtual machine

.. code-block:: bash

  # ssh <IP of VM>

We'll install devstack under $HOME/src/cloud/.

.. code-block:: bash

  # mkdir -p $HOME/src/cloud
  # cd $HOME/src/cloud
  # chmod go+rx $HOME

The Fedora minimal install does not contain git and only
has the crude & old-fashioned "vi" editor.

.. code-block:: bash

  # sudo yum -y install git emacs

At this point a fairly standard devstack setup can be
done. The config below is just an example that is
convenient to use to place everything in $HOME instead
of /opt/stack. Change the IP addresses to something
appropriate for your environment of course

.. code-block:: bash

  # git clone git://github.com/openstack-dev/devstack.git
  # cd devstack
  # cat >>local.conf <<EOF
  [[local|localrc]]
  DEST=$HOME/src/cloud
  DATA_DIR=$DEST/data
  SERVICE_DIR=$DEST/status

  LOGFILE=$DATA_DIR/logs/stack.log
  SCREEN_LOGDIR=$DATA_DIR/logs
  VERBOSE=True

  disable_service neutron

  HOST_IP=192.168.122.50
  FLAT_INTERFACE=eth0
  FIXED_RANGE=192.168.128.0/24
  FIXED_NETWORK_SIZE=256
  FLOATING_RANGE=192.168.129.0/24

  MYSQL_PASSWORD=123456
  SERVICE_TOKEN=123456
  SERVICE_PASSWORD=123456
  ADMIN_PASSWORD=123456
  RABBIT_PASSWORD=123456

  IMAGE_URLS="http://download.cirros-cloud.net/0.3.2/cirros-0.3.2-x86_64-uec.tar.gz"
  EOF

  # FORCE=yes ./stack.sh


Unfortunately while devstack starts various system services and
changes various system settings it doesn't make the changes
persistent. Fix that now to avoid later surprises after reboots

.. code-block:: bash

  # sudo systemctl enable mysqld.service
  # sudo systemctl enable rabbitmq-server.service
  # sudo systemctl enable httpd.service

  # sudo emacs /etc/sysconfig/selinux
  SELINUX=permissive


----------------------------
Testing basis non-NUMA usage
----------------------------

First to confirm we've not done anything unusual to the traditional
operation of Nova libvirt guests boot a tiny instance

.. code-block:: bash

  # . openrc admin admin
  # nova boot --image cirros-0.3.2-x86_64-uec --flavor m1.tiny cirros1

The host will be reporting NUMA topology, but there should only
be a single NUMA cell this point.

.. code-block:: bash

  # mysql -u root -p nova
  MariaDB [nova]> select numa_topology from compute_nodes;
  +------------------------------------------------------------------------------------------------------+
  | numa_topology                                                                                        |
  +------------------------------------------------------------------------------------------------------+
  | {"cells": [{"mem": {"total": 7794, "used": 0}, "cpu_usage": 0, "cpus": "0,1,2,3,4,5,6,7", "id": 0}]} |
  +------------------------------------------------------------------------------------------------------+


Meanwhile, the guest instance should not have any NUMA configuration
recorded

.. code-block:: bash

  MariaDB [nova]> select numa_topology from instance_extra;
  +---------------+
  | numa_topology |
  +---------------+
  | NULL          |
  +---------------+



-----------------------------------------------------
Reconfiguring the test instance to have NUMA topology
-----------------------------------------------------

Now that devstack is proved operational, it is time to configure some
NUMA topology for the test VM, so that it can be used to verify the
OpenStack NUMA support. To do the changes, the VM instance that is running
devstack must be shut down.

.. code-block:: bash

  # sudo shutdown -h now

And now back on the physical host edit the guest config as root

.. code-block:: bash

  # sudo virsh edit f21x86_64

The first thing is to change the <cpu> block to do passthrough of the
host CPU. In particular this exposes the "SVM" or "VMX" feature bits
to the guest so that "Nested KVM" can work. At the same time we want
to define the NUMA topology of the guest. To make things interesting
we're going to give the guest an asymmetric topology with 4 CPUS and
4 GBs of RAM in the first NUMA node and 2 CPUs and 2 GB of RAM in
the second and third NUMA nodes. So modify the guest XML to include
the following CPU XML

.. code-block:: bash

  <cpu mode='host-passthrough'>
    <numa>
      <cell id='0' cpus='0-3' memory='4096000'/>
      <cell id='1' cpus='4-5' memory='2048000'/>
      <cell id='2' cpus='6-7' memory='2048000'/>
    </numa>
  </cpu>

The guest can now be started again, and ssh back into it

.. code-block:: bash

  # virsh start f21x86_64

 ...wait for it to finish booting

  # ssh <IP of VM>


Before starting OpenStack services again, it is necessary to
reconfigure Nova to enable the NUMA schedular filter. The libvirt
virtualization type must also be explicitly set to KVM, so that
guests can take advantage of nested KVM.

.. code-block:: bash

  # sudo emacs /etc/nova/nova.conf

Set the following parameters:

.. code-block:: bash

  [DEFAULT]
  scheduler_default_filters=RetryFilter, AvailabilityZoneFilter, RamFilter, ComputeFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter,ServerGroupAffinityFilter, NUMATopologyFilter

  [libvirt]
  virt_type = kvm


With that done, OpenStack can be started again

.. code-block:: bash

  # cd $HOME/src/cloud/devstack
  # ./rejoin-stack.sh


The first thing is to check that the compute node picked up the
new NUMA topology setup for the guest

.. code-block:: bash

  # mysql -u root -p nova
  MariaDB [nova]> select numa_topology from compute_nodes;
  +--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | numa_topology                                                                                                                                                                                                                                          |
  +--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | {"cells": [{"mem": {"total": 3857, "used": 0}, "cpu_usage": 0, "cpus": "0,1,2,3", "id": 0}, {"mem": {"total": 1969, "used": 0}, "cpu_usage": 0, "cpus": "4,5", "id": 1}, {"mem": {"total": 1967, "used": 0}, "cpu_usage": 0, "cpus": "6,7", "id": 2}]} |
  +--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+


This indeed shows that there are now 3 NUMA nodes for the "host"
machine, the first with 4 GB of RAM and 4 CPUs, and others with
2 GB of RAM and 2 CPUs each.


-----------------------------------------------------
Testing instance boot with no NUMA topology requested
-----------------------------------------------------

For the sake of backwards compatibility, if the NUMA filter is
enabled, but the flavor/image does not have any NUMA settings
requested, it should be assumed that the guest will have a
single NUMA node. The guest should be locked to a single host
NUMA node too. Boot a guest with the m1.tiny flavor to test
this condition

.. code-block:: bash

  # . openrc admin admin
  # nova boot --image cirros-0.3.2-x86_64-uec --flavor m1.tiny cirros1

Now look at the libvirt guest XML. It should show that the vCPUs are
locked to pCPUs within a particular node.

.. code-block:: bash

  # virsh -c qemu:///system list
  ....
  # virsh -c qemu:///system dumpxml instanceXXXXXX
  ...
  <vcpu placement='static' cpuset='6-7'>1</vcpu>
  ...

This example shows that the guest has been locked to the 3rd NUMA
node (which contains pCPUs 6 and 7). Note that there is no explicit
NUMA topology listed in the guest XML.

------------------------------------------------
Testing instance boot with 1 NUMA cell requested
------------------------------------------------

Moving forward a little, explicitly tell Nova that the NUMA topology
for the guest should have a single NUMA node. This should operate
in an identical manner to the default behaviour where no NUMA policy
is set. To define the topology we will create a new flavor

.. code-block:: bash

  # nova flavor-create m1.numa 999 1024 1 4
  # nova flavor-key m1.numa set hw:numa_nodes=1
  # nova flavor-show m1.numa

Now boot the guest using this new flavor

.. code-block:: bash

  # nova boot --image cirros-0.3.2-x86_64-uec --flavor m1.numa cirros2

Looking at the resulting guest XML from libvirt

.. code-block:: bash

  # virsh -c qemu:///system dumpxml instanceXXXXXX
  ...
  <vcpu placement='static'>4</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='0-3'/>
    <vcpupin vcpu='1' cpuset='0-3'/>
    <vcpupin vcpu='2' cpuset='0-3'/>
    <vcpupin vcpu='3' cpuset='0-3'/>
    <emulatorpin cpuset='0-3'/>
  </cputune>
  ...
  <cpu>
    <topology sockets='4' cores='1' threads='1'/>
    <numa>
      <cell id='0' cpus='0-1' memory='524288'/>
      <cell id='1' cpus='2-3' memory='524288'/>
    </numa>
  </cpu>
  ...
  <numatune>
    <memory mode='strict' nodeset='0-1'/>
    <memnode cellid='0' mode='strict' nodeset='0'/>
    <memnode cellid='1' node='strict' nodeset='1'/>
  </numatune>

The XML shows:

* Each guest CPU has been pinned to the physical CPUs
  associated with a particular NUMA node
* The emulator threads have been pinned to the union
  of all physical CPUs in the host NUMA nodes that
  the guest is placed on
* The guest has been given a virtual NUMA topology
  splitting RAM and CPUs symmetrically
* Each guest NUMA node has been strictly pinned to
  a host NUMA node.

As a further sanity test, check what Nova recorded for the
instance in the database. This should match the <numatune>
information

.. code-block:: bash

  MariaDB [nova]> select numa_topology from instance_extra;
  +---------------------------------------------------------------------------------------------------------------+
  | numa_topology                                                                                                 |
  +---------------------------------------------------------------------------------------------------------------+
  | {"cells": [{"mem": {"total": 512}, "cpus": "0,1", "id": 0}, {"mem": {"total": 512}, "cpus": "2,3", "id": 1}]} |
  +---------------------------------------------------------------------------------------------------------------+
