d629b7b5fe
Fix spelling errors in the guide docs. Signed-off-by: John McNamara <john.mcnamara@intel.com> Acked-by: Rami Rosen <ramirose@gmail.com>
119 lines
3.4 KiB
ReStructuredText
119 lines
3.4 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2016 Intel Corporation.
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.. _virtio_user_as_exceptional_path:
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Virtio_user as Exceptional Path
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===============================
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The virtual device, virtio-user, was originally introduced with vhost-user
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backend, as a high performance solution for IPC (Inter-Process Communication)
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and user space container networking.
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Virtio_user with vhost-kernel backend is a solution for exceptional path,
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such as KNI which exchanges packets with kernel networking stack. This
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solution is very promising in:
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* Maintenance
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All kernel modules needed by this solution, vhost and vhost-net (kernel),
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are upstreamed and extensively used kernel module.
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* Features
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vhost-net is born to be a networking solution, which has lots of networking
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related features, like multi queue, tso, multi-seg mbuf, etc.
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* Performance
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similar to KNI, this solution would use one or more kthreads to
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send/receive packets to/from user space DPDK applications, which has little
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impact on user space polling thread (except that it might enter into kernel
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space to wake up those kthreads if necessary).
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The overview of an application using virtio-user as exceptional path is shown
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in :numref:`figure_virtio_user_as_exceptional_path`.
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.. _figure_virtio_user_as_exceptional_path:
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.. figure:: img/virtio_user_as_exceptional_path.*
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Overview of a DPDK app using virtio-user as exceptional path
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Sample Usage
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------------
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As a prerequisite, the vhost/vhost-net kernel CONFIG should be chosen before
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compiling the kernel and those kernel modules should be inserted.
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#. Compile DPDK and bind a physical NIC to igb_uio/uio_pci_generic/vfio-pci.
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This physical NIC is for communicating with outside.
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#. Run testpmd.
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.. code-block:: console
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$(testpmd) -l 2-3 -n 4 \
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--vdev=virtio_user0,path=/dev/vhost-net,queue_size=1024 \
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-- -i --tx-offloads=0x0000002c --enable-lro \
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--txd=1024 --rxd=1024
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This command runs testpmd with two ports, one physical NIC to communicate
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with outside, and one virtio-user to communicate with kernel.
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* ``--enable-lro``
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This is used to negotiate VIRTIO_NET_F_GUEST_TSO4 and
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VIRTIO_NET_F_GUEST_TSO6 feature so that large packets from kernel can be
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transmitted to DPDK application and further TSOed by physical NIC.
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* ``queue_size``
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256 by default. To avoid shortage of descriptors, we can increase it to 1024.
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* ``queues``
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Number of multi-queues. Each queue will be served by a kthread. For example:
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.. code-block:: console
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$(testpmd) -l 2-3 -n 4 \
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--vdev=virtio_user0,path=/dev/vhost-net,queues=2,queue_size=1024 \
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-- -i --tx-offloads=0x0000002c --enable-lro \
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--txq=2 --rxq=2 --txd=1024 --rxd=1024
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#. Enable Rx checksum offloads in testpmd:
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.. code-block:: console
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(testpmd) port stop 0
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(testpmd) port config 0 rx_offload tcp_cksum on
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(testpmd) port config 0 rx_offload udp_cksum on
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(testpmd) port start 0
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#. Start testpmd:
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.. code-block:: console
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(testpmd) start
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#. Configure IP address and start tap:
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.. code-block:: console
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ifconfig tap0 1.1.1.1/24 up
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.. note::
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The tap device will be named tap0, tap1, etc, by kernel.
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Then, all traffic from physical NIC can be forwarded into kernel stack, and all
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traffic on the tap0 can be sent out from physical NIC.
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Limitations
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-----------
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This solution is only available on Linux systems.
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