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doc: add vector fm10k guide

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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>
Acked-by: John McNamara <john.mcnamara@intel.com>
This commit is contained in:
Chen Jing D(Mark) 2016-02-26 13:56:41 +08:00 committed by Thomas Monjalon
parent 81496460b4
commit 995be9512a
1 changed files with 98 additions and 0 deletions
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98
doc/guides/nics/fm10k.rst
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@ -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)''.
The wider register gives space to hold multiple packet buffers so as to save
on the number of instructions when bulk processing packets.
There is no change to the PMD API. The RX/TX handlers are the only two entries for
vPMD packet I/O. They are transparently registered at runtime RX/TX execution
if all required conditions are met.
1. To date, only an SSE version of FM10K vPMD is available.
To ensure that vPMD is in the binary code, set
``CONFIG_RTE_LIBRTE_FM10K_INC_VECTOR=y`` 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 rings will be a power
of 2. With this pre-condition, the ring pointer can easily scroll back to the
head after hitting the tail without a 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 enable via ``RX_OLFLAGS`` use ``RTE_LIBRTE_FM10K_RX_OLFLAGS_ENABLE=y``.
To guarantee the constraint, the following 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 processes 4 packets at a time. So it assumes
that the RX burst should be greater than 4 packets per burst. It returns zero if using
``nb_pkt`` < 4 in the receive handler. If ``nb_pkt`` is not a 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
-----------