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+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright(c) 2010-2015 Intel Corporation.
Poll Mode Driver for Emulated Virtio NIC
========================================
which enables vhost to directly read/ write packets from/to a physical port.
With this enhancement, virtio could achieve quite promising performance.
-In future release, we will also make enhancement to vhost backend,
-releasing peak performance of virtio PMD driver.
-
For basic qemu-KVM installation and other Intel EM poll mode driver in guest VM,
please refer to Chapter "Driver for VM Emulated Devices".
Virtio Implementation in DPDK
-----------------------------
-For details about the virtio spec, refer to Virtio PCI Card Specification written by Rusty Russell.
+For details about the virtio spec, refer to the latest
+`VIRTIO (Virtual I/O) Device Specification
+<https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio>`_.
-As a PMD, virtio provides packet reception and transmission callbacks virtio_recv_pkts and virtio_xmit_pkts.
+As a PMD, virtio provides packet reception and transmission callbacks.
-In virtio_recv_pkts, index in range [vq->vq_used_cons_idx , vq->vq_ring.used->idx) in vring is available for virtio to burst out.
+In Rx, packets described by the used descriptors in vring are available
+for virtio to burst out.
-In virtio_xmit_pkts, same index range in vring is available for virtio to clean.
-Virtio will enqueue to be transmitted packets into vring, advance the vq->vq_ring.avail->idx,
-and then notify the host back end if necessary.
+In Tx, packets described by the used descriptors in vring are available
+for virtio to clean. Virtio will enqueue to be transmitted packets into
+vring, make them available to the device, and then notify the host back
+end if necessary.
Features and Limitations of virtio PMD
--------------------------------------
* It supports multicast packets and promiscuous mode.
-* The descriptor number for the RX/TX queue is hard-coded to be 256 by qemu.
+* The descriptor number for the Rx/Tx queue is hard-coded to be 256 by qemu 2.7 and below.
If given a different descriptor number by the upper application,
the virtio PMD generates a warning and fall back to the hard-coded value.
+ Rx queue size can be configurable and up to 1024 since qemu 2.8 and above. Rx queue size is 256
+ by default. Tx queue size is still hard-coded to be 256.
* Features of mac/vlan filter are supported, negotiation with vhost/backend are needed to support them.
- When backend can't support vlan filter, virtio app on guest should disable vlan filter to make sure
- the virtio port is configured correctly. E.g. specify '--disable-hw-vlan' in testpmd command line.
+ When backend can't support vlan filter, virtio app on guest should not enable vlan filter in order
+ to make sure the virtio port is configured correctly. E.g. do not specify '--enable-hw-vlan' in testpmd
+ command line. Note that, mac/vlan filter is best effort: unwanted packets could still arrive.
-* RTE_PKTMBUF_HEADROOM should be defined larger than sizeof(struct virtio_net_hdr), which is 10 bytes.
+* "RTE_PKTMBUF_HEADROOM" should be defined
+ no less than "sizeof(struct virtio_net_hdr_mrg_rxbuf)", which is 12 bytes when mergeable or
+ "VIRTIO_F_VERSION_1" is set.
+ no less than "sizeof(struct virtio_net_hdr)", which is 10 bytes, when using non-mergeable.
* Virtio does not support runtime configuration.
* Virtio supports Link State interrupt.
+* Virtio supports Rx interrupt (so far, only support 1:1 mapping for queue/interrupt).
+
* Virtio supports software vlan stripping and inserting.
* Virtio supports using port IO to get PCI resource when uio/igb_uio module is not available.
.. code-block:: console
- examples/kni/build/app/kni -c 0xf -n 4 -- -p 0x1 -P --config="(0,1,3)"
+ examples/kni/build/app/kni -l 0-3 -n 4 -- -p 0x1 -P --config="(0,1,3)"
This command generates one network device vEth0 for physical port.
If specify more physical ports, the generated network device will be vEth1, vEth2, and so on.
which means received packets come from vEth0, and transmitted packets is sent to vEth0.
#. In the guest, bind the virtio device to the uio_pci_generic kernel module and start the forwarding application.
- When the virtio port in guest bursts rx, it is getting packets from the raw socket's receive queue.
- When the virtio port bursts tx, it is sending packet to the tx_q.
+ When the virtio port in guest bursts Rx, it is getting packets from the
+ raw socket's receive queue.
+ When the virtio port bursts Tx, it is sending packet to the tx_q.
.. code-block:: console
modprobe uio
echo 512 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
modprobe uio_pci_generic
- python tools/dpdk_nic_bind.py -b uio_pci_generic 00:03.0
+ python usertools/dpdk-devbind.py -b uio_pci_generic 00:03.0
We use testpmd as the forwarding application in this example.
The packet reception and transmission flow path is:
- IXIA packet generator->82599 PF->KNI rx queue->KNI raw socket queue->Guest VM virtio port 0 rx burst->Guest VM virtio port 0 tx burst-> KNI tx queue->82599 PF-> IXIA packet generator
+ IXIA packet generator->82599 PF->KNI Rx queue->KNI raw socket queue->Guest
+ VM virtio port 0 Rx burst->Guest VM virtio port 0 Tx burst-> KNI Tx queue
+ ->82599 PF-> IXIA packet generator
Virtio with qemu virtio Back End
--------------------------------
In this example, the packet reception flow path is:
- IXIA packet generator->82599 PF->Linux Bridge->TAP0's socket queue-> Guest VM virtio port 0 rx burst-> Guest VM 82599 VF port1 tx burst-> IXIA packet generator
+ IXIA packet generator->82599 PF->Linux Bridge->TAP0's socket queue-> Guest
+ VM virtio port 0 Rx burst-> Guest VM 82599 VF port1 Tx burst-> IXIA packet
+ generator
The packet transmission flow is:
- IXIA packet generator-> Guest VM 82599 VF port1 rx burst-> Guest VM virtio port 0 tx burst-> tap -> Linux Bridge->82599 PF-> IXIA packet generator
+ IXIA packet generator-> Guest VM 82599 VF port1 Rx burst-> Guest VM virtio
+ port 0 Tx burst-> tap -> Linux Bridge->82599 PF-> IXIA packet generator
+
+
+Virtio PMD Rx/Tx Callbacks
+--------------------------
+
+Virtio driver has 6 Rx callbacks and 3 Tx callbacks.
+
+Rx callbacks:
+
+#. ``virtio_recv_pkts``:
+ Regular version without mergeable Rx buffer support for split virtqueue.
+
+#. ``virtio_recv_mergeable_pkts``:
+ Regular version with mergeable Rx buffer support for split virtqueue.
+
+#. ``virtio_recv_pkts_vec``:
+ Vector version without mergeable Rx buffer support, also fixes the available
+ ring indexes and uses vector instructions to optimize performance for split
+ virtqueue.
+
+#. ``virtio_recv_pkts_inorder``:
+ In-order version with mergeable and non-mergeable Rx buffer support
+ for split virtqueue.
+
+#. ``virtio_recv_pkts_packed``:
+ Regular and in-order version without mergeable Rx buffer support for
+ packed virtqueue.
+
+#. ``virtio_recv_mergeable_pkts_packed``:
+ Regular and in-order version with mergeable Rx buffer support for packed
+ virtqueue.
+
+Tx callbacks:
+
+#. ``virtio_xmit_pkts``:
+ Regular version for split virtqueue.
+
+#. ``virtio_xmit_pkts_inorder``:
+ In-order version for split virtqueue.
+
+#. ``virtio_xmit_pkts_packed``:
+ Regular and in-order version for packed virtqueue.
+
+By default, the non-vector callbacks are used:
+
+* For Rx: If mergeable Rx buffers is disabled then ``virtio_recv_pkts``
+ or ``virtio_recv_pkts_packed`` will be used, otherwise
+ ``virtio_recv_mergeable_pkts`` or ``virtio_recv_mergeable_pkts_packed``
+ will be used.
+
+* For Tx: ``virtio_xmit_pkts`` or ``virtio_xmit_pkts_packed`` will be used.
+
+
+Vector callbacks will be used when:
+
+* Mergeable Rx buffers is disabled.
+
+The corresponding callbacks are:
+
+* For Rx: ``virtio_recv_pkts_vec``.
+
+There is no vector callbacks for packed virtqueue for now.
+
+
+Example of using the vector version of the virtio poll mode driver in
+``testpmd``::
+
+ testpmd -l 0-2 -n 4 -- -i --rxq=1 --txq=1 --nb-cores=1
+
+In-order callbacks only work on simulated virtio user vdev.
+
+For split virtqueue:
+
+* For Rx: If in-order is enabled then ``virtio_recv_pkts_inorder`` is used.
+
+* For Tx: If in-order is enabled then ``virtio_xmit_pkts_inorder`` is used.
+
+For packed virtqueue, the default callbacks already support the
+in-order feature.
+
+Interrupt mode
+--------------
+
+.. _virtio_interrupt_mode:
+
+There are three kinds of interrupts from a virtio device over PCI bus: config
+interrupt, Rx interrupts, and Tx interrupts. Config interrupt is used for
+notification of device configuration changes, especially link status (lsc).
+Interrupt mode is translated into Rx interrupts in the context of DPDK.
+
+.. Note::
+
+ Virtio PMD already has support for receiving lsc from qemu when the link
+ status changes, especially when vhost user disconnects. However, it fails
+ to do that if the VM is created by qemu 2.6.2 or below, since the
+ capability to detect vhost user disconnection is introduced in qemu 2.7.0.
+
+Prerequisites for Rx interrupts
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To support Rx interrupts,
+#. Check if guest kernel supports VFIO-NOIOMMU:
+
+ Linux started to support VFIO-NOIOMMU since 4.8.0. Make sure the guest
+ kernel is compiled with:
+
+ .. code-block:: console
+
+ CONFIG_VFIO_NOIOMMU=y
+
+#. Properly set msix vectors when starting VM:
+
+ Enable multi-queue when starting VM, and specify msix vectors in qemu
+ cmdline. (N+1) is the minimum, and (2N+2) is mostly recommended.
+
+ .. code-block:: console
+
+ $(QEMU) ... -device virtio-net-pci,mq=on,vectors=2N+2 ...
+
+#. In VM, insert vfio module in NOIOMMU mode:
+
+ .. code-block:: console
+
+ modprobe vfio enable_unsafe_noiommu_mode=1
+ modprobe vfio-pci
+
+#. In VM, bind the virtio device with vfio-pci:
+
+ .. code-block:: console
+
+ python usertools/dpdk-devbind.py -b vfio-pci 00:03.0
+
+Example
+~~~~~~~
+
+Here we use l3fwd-power as an example to show how to get started.
+
+ Example:
+
+ .. code-block:: console
+
+ $ l3fwd-power -l 0-1 -- -p 1 -P --config="(0,0,1)" \
+ --no-numa --parse-ptype
+
+
+Virtio PMD arguments
+--------------------
+
+Below devargs are supported by the PCI virtio driver:
+
+#. ``vdpa``:
+
+ A virtio device could also be driven by vDPA (vhost data path acceleration)
+ driver, and works as a HW vhost backend. This argument is used to specify
+ a virtio device needs to work in vDPA mode.
+ (Default: 0 (disabled))
+
+Below devargs are supported by the virtio-user vdev:
+
+#. ``path``:
+
+ It is used to specify a path to connect to vhost backend.
+
+#. ``mac``:
+
+ It is used to specify the MAC address.
+
+#. ``cq``:
+
+ It is used to enable the control queue. (Default: 0 (disabled))
+
+#. ``queue_size``:
+
+ It is used to specify the queue size. (Default: 256)
+
+#. ``queues``:
+
+ It is used to specify the queue number. (Default: 1)
+
+#. ``iface``:
+
+ It is used to specify the host interface name for vhost-kernel
+ backend.
+
+#. ``server``:
+
+ It is used to enable the server mode when using vhost-user backend.
+ (Default: 0 (disabled))
+
+#. ``mrg_rxbuf``:
+
+ It is used to enable virtio device mergeable Rx buffer feature.
+ (Default: 1 (enabled))
+
+#. ``in_order``:
+
+ It is used to enable virtio device in-order feature.
+ (Default: 1 (enabled))
+
+#. ``packed_vq``:
+
+ It is used to enable virtio device packed virtqueue feature.
+ (Default: 0 (disabled))
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