171 lines
5.9 KiB
ReStructuredText
171 lines
5.9 KiB
ReStructuredText
======================
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Other libvirt features
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======================
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The libvirt driver supports a large number of additional features that don't
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warrant their own section. These are gathered here.
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Guest agent support
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-------------------
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Guest agents enable optional access between compute nodes and guests through a
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socket, using the QMP protocol.
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To enable this feature, you must set ``hw_qemu_guest_agent=yes`` as a metadata
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parameter on the image you wish to use to create the guest-agent-capable
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instances from. You can explicitly disable the feature by setting
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``hw_qemu_guest_agent=no`` in the image metadata.
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.. _extra-specs-watchdog-behavior:
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Watchdog behavior
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-----------------
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.. versionchanged:: 15.0.0 (Ocata)
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Add support for the ``disabled`` option.
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A virtual watchdog device can be used to keep an eye on the guest server and
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carry out a configured action if the server hangs. The watchdog uses the
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i6300esb device (emulating a PCI Intel 6300ESB). Watchdog behavior can be
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configured using the :nova:extra-spec:`hw:watchdog_action` flavor extra spec or
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equivalent image metadata property. If neither the extra spec not the image
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metadata property are specified, the watchdog is disabled.
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For example, to enable the watchdog and configure it to forcefully reset the
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guest in the event of a hang, run:
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.. code-block:: console
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$ openstack flavor set $FLAVOR --property hw:watchdog_action=reset
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.. note::
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Watchdog behavior set using the image metadata property will override
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behavior set using the flavor extra spec.
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.. _extra-specs-random-number-generator:
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Random number generator
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-----------------------
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.. versionchanged:: 21.0.0 (Ussuri)
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Random number generators are now enabled by default for instances.
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Operating systems require good sources of entropy for things like cryptographic
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software. If a random-number generator device has been added to the instance
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through its image properties, the device can be enabled and configured using
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the :nova:extra-spec:`hw_rng:allowed`, :nova:extra-spec:`hw_rng:rate_bytes` and
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:nova:extra-spec:`hw_rng:rate_period` flavor extra specs.
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To configure for example a byte rate of 5 bytes per period and a period of 1000
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mSec (1 second), run:
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.. code-block:: console
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$ openstack flavor set $FLAVOR \
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--property hw_rng:rate_bytes=5 \
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--property hw_rng:rate_period=1000
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Alternatively, to disable the random number generator, run:
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.. code-block:: console
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$ openstack flavor set $FLAVOR --property hw_rng:allowed=false
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The presence of separate byte rate and rate period configurables is
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intentional. As noted in the `QEMU docs`__, a smaller rate and larger period
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minimizes the opportunity for malicious guests to starve other guests of
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entropy but at the cost of responsiveness. Conversely, larger rates and smaller
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periods will increase the burst rate but at the potential cost of warping
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resource consumption in favour of a greedy guest.
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.. __: https://wiki.qemu.org/Features/VirtIORNG#Effect_of_the_period_parameter
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.. _extra-specs-performance-monitoring-unit:
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Performance Monitoring Unit (vPMU)
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----------------------------------
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.. versionadded:: 20.0.0 (Train)
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If nova is deployed with the libvirt virt driver and
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:oslo.config:option:`libvirt.virt_type` is set to ``qemu`` or ``kvm``, a
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virtual performance monitoring unit (vPMU) can be enabled or disabled for an
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instance using the :nova:extra-spec:`hw:pmu` flavor extra spec or ``hw_pmu``
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image metadata property.
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If the vPMU is not explicitly enabled or disabled via
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the flavor or image, its presence is left to QEMU to decide.
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For example, to explicitly disable the vPMU, run:
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.. code-block:: console
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$ openstack flavor set FLAVOR-NAME --property hw:pmu=false
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The vPMU is used by tools like ``perf`` in the guest to provide more accurate
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information for profiling application and monitoring guest performance.
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For :doc:`real time </admin/real-time>` workloads, the emulation of a vPMU can
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introduce additional latency which would be undesirable. If the telemetry it
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provides is not required, the vPMU can be disabled. For most workloads the
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default of unset (enabled) will be correct.
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.. _extra-specs-hiding-hypervisor-signature:
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Hiding hypervisor signature
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---------------------------
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.. versionadded:: 18.0.0 (Rocky)
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.. versionchanged:: 21.0.0 (Ussuri)
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Prior to the Ussuri release, this was called ``hide_hypervisor_id``. An
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alias is provided to provide backwards compatibility.
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Some hypervisors add a signature to their guests. While the presence of the
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signature can enable some paravirtualization features on the guest, it can also
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have the effect of preventing some drivers from loading. You can hide this
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signature by setting the :nova:extra-spec:`hw:hide_hypervisor_id` to true.
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For example, to hide your signature from the guest OS, run:
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.. code:: console
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$ openstack flavor set $FLAVOR --property hw:hide_hypervisor_id=true
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.. _extra-spec-locked_memory:
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Locked memory allocation
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------------------------
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.. versionadded:: 26.0.0 (Zed)
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Locking memory marks the guest memory allocations as unmovable and
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unswappable. It is implicitly enabled in a number of cases such as SEV or
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realtime guests but can also be enabled explicitly using the
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``hw:locked_memory`` extra spec (or use ``hw_locked_memory`` image property).
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``hw:locked_memory`` (also ``hw_locked_memory`` image property) accept
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boolean values in string format like 'true' or 'false' value.
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It will raise `FlavorImageLockedMemoryConflict` exception if both flavor and
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image property are specified but with different boolean values.
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This will only be allowed if you have also set ``hw:mem_page_size``,
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so we can ensure that the scheduler can actually account for this correctly
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and prevent out of memory events. Otherwise, will raise `LockMemoryForbidden`
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exception.
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.. code:: console
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$ openstack flavor set FLAVOR-NAME \
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--property hw:locked_memory=BOOLEAN_VALUE
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.. note::
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This is currently only supported by the libvirt driver.
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