[dpdk-dev] [PATCH] doc: virtio pmd versions

[Zhihong Wang <zhihong.wang@intel.com>]

This patch explains all the versions of current virtio pmd implementation,
what's the difference, and how to choose the right version.

Signed-off-by: Zhihong Wang <zhihong.wang@intel.com>
---
 doc/guides/nics/virtio.rst | 57 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/doc/guides/nics/virtio.rst b/doc/guides/nics/virtio.rst
index 06ca433..43ba686 100644
--- a/doc/guides/nics/virtio.rst
+++ b/doc/guides/nics/virtio.rst
@@ -211,3 +211,60 @@ In this example, the packet reception flow path is:
 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
+
+Virtio PMD Versions
+-------------------
+
+Virtio driver has 3 versions of rx functions and 2 versions of tx functions.
+
+RX functions:
+
+*   ``virtio_recv_pkts``:
+
+    Regular version without mergeable rx buffers support
+
+*   ``virtio_recv_mergeable_pkts``:
+
+    Regular version with mergeable rx buffers support
+
+*   ``virtio_recv_pkts_vec``:
+
+    Simple version without mergeable rx buffers support, also fixes the avail ring and uses vector instructions to optimize performance
+
+TX functions:
+
+*   ``virtio_xmit_pkts``:
+
+    Regular version
+
+*   ``virtio_xmit_pkts_simple``:
+
+    Simple version fixes the avail ring to optimize performance
+
+By default, the non-vector versions 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``
+
+Setting ``txq_flags`` to ``VIRTIO_SIMPLE_FLAGS`` (0xf01) enables the simple version of virtio poll mode driver:
+
+*   For rx: ``virtio_recv_pkts_vec``
+
+*   For tx: ``virtio_xmit_pkts_simple``
+
+The simple version will only be enabled when:
+
+*   Mergeable rx buffers is disabled
+
+*   Single segment is specified
+
+*   No offload support is needed
+
+Example to use the simple version of virtio poll mode driver in testpmd:
+
+.. code-block:: console
+
+./x86_64-native-linuxapp-gcc/app/testpmd -c 0x7 -n 4
+    --  -i --txqflags=0xf01 --rxq=1 --txq=1 --nb-cores=1
+
-- 
2.5.0