+ 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 3 Rx callbacks and 2 Tx callbacks.
+
+Rx callbacks:
+
+#. ``virtio_recv_pkts``:
+ Regular version without mergeable Rx buffer support.
+
+#. ``virtio_recv_mergeable_pkts``:
+ Regular version with mergeable Rx buffer support.
+
+#. ``virtio_recv_pkts_vec``:
+ Vector version without mergeable Rx buffer support, also fixes the available
+ ring indexes and uses vector instructions to optimize performance.
+
+Tx callbacks:
+
+#. ``virtio_xmit_pkts``:
+ Regular version.
+
+#. ``virtio_xmit_pkts_simple``:
+ Vector version fixes the available ring indexes to optimize performance.
+
+
+By default, the non-vector callbacks are used:
+
+* For Rx: If mergeable Rx buffers is disabled then ``virtio_recv_pkts`` is
+ used; otherwise ``virtio_recv_mergeable_pkts``.
+
+* For Tx: ``virtio_xmit_pkts``.
+
+
+Vector callbacks will be used when:
+
+* ``txq_flags`` is set to ``VIRTIO_SIMPLE_FLAGS`` (0xF01), which implies:
+
+ * Single segment is specified.
+
+ * No offload support is needed.
+
+* Mergeable Rx buffers is disabled.
+
+The corresponding callbacks are:
+
+* For Rx: ``virtio_recv_pkts_vec``.
+
+* For Tx: ``virtio_xmit_pkts_simple``.
+
+
+Example of using the vector version of the virtio poll mode driver in
+``testpmd``::
+
+ testpmd -c 0x7 -n 4 -- -i --txqflags=0xF01 --rxq=1 --txq=1 --nb-cores=1
+
+
+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.
+
+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 tools/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 -c 0x3 -- -p 1 -P --config="(0,0,1)" \
+ --no-numa --parse-ptype