12b6ff7cd4
This commit includes the creation of a doc about how the agent operates and how to configure OpenStack to operate properly with it. Fixed minor editorial issues. Signed-off-by: Elisamara Aoki Goncalves <elisamaraaoki.goncalves@windriver.com> Change-Id: Ie118b1b2b7924a7f3a94bec089cd315094ebdef2
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58 lines
2.1 KiB
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.. _pci-irq-affinity-4fed257d094b:
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================
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PCI IRQ Affinity
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================
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While in OpenStack it is possible to enable instances to use |PCI| devices, the
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interrupts generated by these devices may be handled by host CPUs that are
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unrelated to the instance, and this can lead to noisy neighbor issues and lower
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performance, if the device interrupts were handled by the instance's CPUs.
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|PCI| |IRQ| Affinity can only be specified for instances with dedicated vCPUs.
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|PCI| |IRQ| Affinity assignments are used to achieve higher performance since
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the instance's core(s) will handle the interrupts from |PCI| devices used
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by these instances. Interrupts are thus prevented from consuming cycles on the
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platform cores.
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-----------
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Flavor spec
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-----------
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A specific flavor spec for |PCI| interrupt affining is used to determine which
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vCPUs assigned to the instance must handle the interrupts from the |PCI|
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devices:
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``hw:pci_irq_affinity_mask=<vcpus_cpulist>``
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Where ``vcpus_cpulist`` can assume a comma-separated list of values that
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can be expressed as:
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- ``int``: the vCPU expressed by ``int`` will be assigned to handle the
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interruptions from the |PCI| devices
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- ``int1-int2``: the vCPUs between ``int1`` and ``int2`` (inclusive) will
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be used to handle the interruptions from the |PCI| devices
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- ``^int``: the vCPU expressed by ``int`` will not be assigned to handle the
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interruptions from the |PCI| devices and shall be used to exclude a vCPU
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that was included in a previous range
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.. note::
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``int`` must be a value between ``0`` and ``flavor.vcpus - 1``.
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For example: ``hw_pci_irq_affinity_mask=1-4,^3,6`` means that vCPUs with
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indexes ``1,2,4 and 6`` from the vCPU list that Nova allocates to the instance
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will be assigned to handle interruptions from the |PCI| devices.
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-----------
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Limitations
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-----------
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- No |PCI| |IRQ| CPU affining is supported for instances using shared CPUs
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(i.e., when using flavor spec ``hw:cpu_policy=shared``).
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- No |PCI| |IRQ| CPU affining will be performed when invalid ranges are
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specified in the flavor spec; a log error message will be generated
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indicating the problem.
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