88 lines
3.6 KiB
ReStructuredText
88 lines
3.6 KiB
ReStructuredText
.. _enable-ptm:
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Enable PCIe Precision Time Management
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#####################################
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The PCI Express (PCIe) specification defines a Precision Time Measurement (PTM)
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mechanism that lets you coordinate and synchronize events across multiple PCI
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components within the same system with very fine time precision.
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ACRN adds PCIe root port emulation in the hypervisor to support the PTM feature
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and emulates a simple PTM hierarchy. ACRN enables PTM in a Guest VM if the user
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sets the ``enable_ptm`` option when passing through a device to a post-launched
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VM and :ref:`vm.PTM` is enabled in the scenario configuration. When you enable
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PTM, the passthrough device is connected to a virtual root port instead of the host
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bridge as it normally would.
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Here is an example launch script that configures a supported Ethernet card for
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passthrough and enables PTM on it:
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.. code-block:: bash
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:emphasize-lines: 9-11,17
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declare -A passthru_vpid
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declare -A passthru_bdf
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passthru_vpid=(
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["ethptm"]="8086 15f2"
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)
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passthru_bdf=(
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["ethptm"]="0000:aa:00.0"
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)
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echo ${passthru_vpid["ethptm"]} > /sys/bus/pci/drivers/pci-stub/new_id
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echo ${passthru_bdf["ethptm"]} > /sys/bus/pci/devices/${passthru_bdf["ethptm"]}/driver/unbind
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echo ${passthru_bdf["ethptm"]} > /sys/bus/pci/drivers/pci-stub/bind
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acrn-dm -A -m $mem_size -s 0:0,hostbridge \
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-s 3,virtio-blk,uos-test.img \
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-s 4,virtio-net,tap0 \
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-s 5,virtio-console,@stdio:stdio_port \
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-s 6,passthru,a9/00/0,enable_ptm \
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--ovmf /usr/share/acrn/bios/OVMF.fd
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.. important:: By default, the :ref:`vm.PTM` option is disabled in ACRN VMs. Use the
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:ref:`ACRN configuration tool <acrn_configuration_tool>` to enable PTM
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in the scenario XML file that configures the Guest VM.
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Here is the bus hierarchy in the Guest VM (as shown by the ``lspci`` command)::
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lspci -tv
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-[0000:00]-+-00.0 Network Appliance Corporation Device 1275
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+-03.0 Red Hat, Inc. Virtio block device
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+-04.0 Red Hat, Inc. Virtio network device
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+-05.0 Red Hat, Inc. Virtio console
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\-06.0-[01]----00.0 Intel Corporation Device 15f2
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(Instead of ``Device 15f2`` you might see ``Ethernet Controller I225LM``.)
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You can also verify that PTM was enabled by using ``dmesg`` in the guest VM::
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dmesg | grep -i ptm
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[ 1.555284] pci_ptm_init: 00:00.00, ispcie=1, type=0x4
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[ 1.555356] Cannot find PTM ext cap.
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[ 1.561311] pci_ptm_init: 00:03.00, ispcie=0, type=0x0
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[ 1.567146] pci_ptm_init: 00:04.00, ispcie=0, type=0x0
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[ 1.572983] pci_ptm_init: 00:05.00, ispcie=0, type=0x0
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[ 1.718038] pci_ptm_init: 00:06.00, ispcie=1, type=0x4
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[ 1.722034] ptm is ptm_root.
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[ 1.723033] Condition-2: ptm is enabled.
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[ 1.723052] pci 0000:00:06.0: PTM enabled (root), 4ns granularity
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[ 1.766438] pci_ptm_init: a9:00.00, ispcie=1, type=0x0
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[ 5.715000] igc_probe enable ptm.
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[ 5.715068] pci_enable_ptm: a9:00.00, ispcie=1, type=0x0
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[ 5.715294] ptm is enabled on endpoint device.
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[ 5.715371] igc 0000:a9:00.0: PTM enabled, 4ns granularity
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PTM Implementation Notes
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************************
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To simplify the implementation, the virtual root port only supports the most
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basic PCIe configuration and operation, in addition to PTM capabilities.
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To use PTM in a virtualized environment, you may want to first verify that PTM
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is supported by the device and is enabled on the bare metal machine and in the
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Guest VM kernel (e.g., ``CONFIG_PCIE_PTM=y`` option is set in the Linux kernel).
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You can find more details about the PTM implementation in the
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:ref:`ACRN HLD PCIe PTM documentation <PCIe PTM implementation>`.
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