[dpdk-dev] [PATCH v2] doc: add Vector FM10K introductions

["Chen Jing D(Mark)" <jing.d.chen@intel.com>]

From: "Chen Jing D(Mark)" <jing.d.chen@intel.com>

Add introductions on how to enable Vector FM10K Rx/Tx functions,
the preconditions and assumptions on Rx/Tx configuration parameters.
The new content also lists the limitations of vector, so app/customer
can do better to select best Rx/Tx functions.

Signed-off-by: Chen Jing D(Mark) <jing.d.chen@intel.com>
---
v2:
 - rebase to latest repo
 - Reword a few sentences that not follow coding style.

 doc/guides/nics/fm10k.rst |   98 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 98 insertions(+), 0 deletions(-)

diff --git a/doc/guides/nics/fm10k.rst b/doc/guides/nics/fm10k.rst
index 4206b7f..a502ffd 100644
--- a/doc/guides/nics/fm10k.rst
+++ b/doc/guides/nics/fm10k.rst
@@ -35,6 +35,104 @@ The FM10K poll mode driver library provides support for the Intel FM10000
 (FM10K) family of 40GbE/100GbE adapters.
 
 
+Vector PMD for FM10K
+--------------------
+
+Vector PMD (vPMD) uses Intel® SIMD instructions to optimize packet I/O.
+It improves load/store bandwidth efficiency of L1 data cache by using a wider
+SSE/AVX register 1 (1).
+The wider register gives space to hold multiple packet buffers so as to save
+instruction number when processing bulk of packets.
+
+There is no change to PMD API. The RX/TX handler are the only two entries for
+vPMD packet I/O. They are transparently registered at runtime RX/TX execution
+if all condition checks pass.
+
+1.  To date, only an SSE version of FM10K vPMD is available.
+    To ensure that vPMD is in the binary code, ensure that the option
+    CONFIG_RTE_LIBRTE_FM10K_INC_VECTOR=y is in the configure file.
+
+Some constraints apply as pre-conditions for specific optimizations on bulk
+packet transfers. The following sections explain RX and TX constraints in the
+vPMD.
+
+
+RX Constraints
+~~~~~~~~~~~~~~
+
+
+Prerequisites and Pre-conditions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+For Vector RX it is assumed that the number of descriptor ring will be power
+of 2. With this pre-condition, the ring pointer can easily scroll back to the
+head after hitting the tail without conditional check. In addition Vector RX
+can use this assumption to do a bit mask using ``ring_size - 1``.
+
+
+Features not Supported by Vector RX PMD
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Some features are not supported when trying to increase the throughput in
+vPMD. They are:
+
+*   IEEE1588
+
+*   Flow director
+
+*   Header split
+
+*   RX checksum offload
+
+Other features are supported using optional MACRO configuration. They include:
+
+*   HW VLAN strip
+
+*   L3/L4 packet type
+
+To enabled by RX_OLFLAGS use ``RTE_LIBRTE_FM10K_RX_OLFLAGS_ENABLE=y``.
+
+To guarantee the constraint, the configuration flags in ``dev_conf.rxmode``
+will be checked:
+
+*   ``hw_vlan_extend``
+
+*   ``hw_ip_checksum``
+
+*   ``header_split``
+
+*   ``fdir_conf->mode``
+
+
+RX Burst Size
+^^^^^^^^^^^^^
+
+As vPMD is focused on high throughput, it 4 packets at a time.  So it assumes
+that the RX burst should be greater than 4 per burst. It returns zero if using
+``nb_pkt`` < 4 in the receive handler. If ``nb_pkt`` is not multiple of 4, a
+floor alignment will be applied.
+
+
+TX Constraint
+~~~~~~~~~~~~~
+
+Features not Supported by TX Vector PMD
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+TX vPMD only works when ``txq_flags`` is set to ``FM10K_SIMPLE_TX_FLAG``.
+This means that it does not support TX multi-segment, VLAN offload or TX csum
+offload. The following MACROs are used for these three features:
+
+*   ``ETH_TXQ_FLAGS_NOMULTSEGS``
+
+*   ``ETH_TXQ_FLAGS_NOVLANOFFL``
+
+*   ``ETH_TXQ_FLAGS_NOXSUMSCTP``
+
+*   ``ETH_TXQ_FLAGS_NOXSUMUDP``
+
+*   ``ETH_TXQ_FLAGS_NOXSUMTCP``
+
 Limitations
 -----------
 
-- 
1.7.7.6