import 15.2.0 Octopus source

[ceph.git] / ceph / src / seastar / dpdk / doc / guides / nics / i40e.rst

..  SPDX-License-Identifier: BSD-3-Clause
    Copyright(c) 2016 Intel Corporation.

I40E Poll Mode Driver
======================

The i40e PMD (librte_pmd_i40e) provides poll mode driver support for
10/25/40 Gbps Intel® Ethernet 700 Series Network Adapters based on
the Intel Ethernet Controller X710/XL710/XXV710 and Intel Ethernet
Connection X722 (only support part of features).


Features
--------

Features of the i40e PMD are:

- Multiple queues for TX and RX
- Receiver Side Scaling (RSS)
- MAC/VLAN filtering
- Packet type information
- Flow director
- Cloud filter
- Checksum offload
- VLAN/QinQ stripping and inserting
- TSO offload
- Promiscuous mode
- Multicast mode
- Port hardware statistics
- Jumbo frames
- Link state information
- Link flow control
- Mirror on port, VLAN and VSI
- Interrupt mode for RX
- Scattered and gather for TX and RX
- Vector Poll mode driver
- DCB
- VMDQ
- SR-IOV VF
- Hot plug
- IEEE1588/802.1AS timestamping
- VF Daemon (VFD) - EXPERIMENTAL
- Dynamic Device Personalization (DDP)
- Queue region configuration
- Virtual Function Port Representors

Prerequisites
-------------

- Identifying your adapter using `Intel Support
  <http://www.intel.com/support>`_ and get the latest NVM/FW images.

- Follow the DPDK :ref:`Getting Started Guide for Linux <linux_gsg>` to setup the basic DPDK environment.

- To get better performance on Intel platforms, please follow the "How to get best performance with NICs on Intel platforms"
  section of the :ref:`Getting Started Guide for Linux <linux_gsg>`.

- Upgrade the NVM/FW version following the `Intel® Ethernet NVM Update Tool Quick Usage Guide for Linux
  <https://www-ssl.intel.com/content/www/us/en/embedded/products/networking/nvm-update-tool-quick-linux-usage-guide.html>`_ and `Intel® Ethernet NVM Update Tool: Quick Usage Guide for EFI <https://www.intel.com/content/www/us/en/embedded/products/networking/nvm-update-tool-quick-efi-usage-guide.html>`_ if needed.

Recommended Matching List
-------------------------

It is highly recommended to upgrade the i40e kernel driver and firmware to
avoid the compatibility issues with i40e PMD. Here is the suggested matching
list which has been tested and verified. The detailed information can refer
to chapter Tested Platforms/Tested NICs in release notes.

   +--------------+-----------------------+------------------+
   | DPDK version | Kernel driver version | Firmware version |
   +==============+=======================+==================+
   |    19.05     |         2.7.29        |       6.80       |
   +--------------+-----------------------+------------------+
   |    19.02     |         2.7.26        |       6.80       |
   +--------------+-----------------------+------------------+
   |    18.11     |         2.4.6         |       6.01       |
   +--------------+-----------------------+------------------+
   |    18.08     |         2.4.6         |       6.01       |
   +--------------+-----------------------+------------------+
   |    18.05     |         2.4.6         |       6.01       |
   +--------------+-----------------------+------------------+
   |    18.02     |         2.4.3         |       6.01       |
   +--------------+-----------------------+------------------+
   |    17.11     |         2.1.26        |       6.01       |
   +--------------+-----------------------+------------------+
   |    17.08     |         2.0.19        |       6.01       |
   +--------------+-----------------------+------------------+
   |    17.05     |         1.5.23        |       5.05       |
   +--------------+-----------------------+------------------+
   |    17.02     |         1.5.23        |       5.05       |
   +--------------+-----------------------+------------------+
   |    16.11     |         1.5.23        |       5.05       |
   +--------------+-----------------------+------------------+
   |    16.07     |         1.4.25        |       5.04       |
   +--------------+-----------------------+------------------+
   |    16.04     |         1.4.25        |       5.02       |
   +--------------+-----------------------+------------------+

Pre-Installation Configuration
------------------------------

Config File Options
~~~~~~~~~~~~~~~~~~~

The following options can be modified in the ``config`` file.
Please note that enabling debugging options may affect system performance.

- ``CONFIG_RTE_LIBRTE_I40E_PMD`` (default ``y``)

  Toggle compilation of the ``librte_pmd_i40e`` driver.

- ``CONFIG_RTE_LIBRTE_I40E_DEBUG_*`` (default ``n``)

  Toggle display of generic debugging messages.

- ``CONFIG_RTE_LIBRTE_I40E_RX_ALLOW_BULK_ALLOC`` (default ``y``)

  Toggle bulk allocation for RX.

- ``CONFIG_RTE_LIBRTE_I40E_INC_VECTOR`` (default ``n``)

  Toggle the use of Vector PMD instead of normal RX/TX path.
  To enable vPMD for RX, bulk allocation for Rx must be allowed.

- ``CONFIG_RTE_LIBRTE_I40E_16BYTE_RX_DESC`` (default ``n``)

  Toggle to use a 16-byte RX descriptor, by default the RX descriptor is 32 byte.

- ``CONFIG_RTE_LIBRTE_I40E_QUEUE_NUM_PER_PF`` (default ``64``)

  Number of queues reserved for PF.

- ``CONFIG_RTE_LIBRTE_I40E_QUEUE_NUM_PER_VM`` (default ``4``)

  Number of queues reserved for each VMDQ Pool.

Runtime Config Options
~~~~~~~~~~~~~~~~~~~~~~

- ``Reserved number of Queues per VF`` (default ``4``)

  The number of reserved queue per VF is determined by its host PF. If the
  PCI address of an i40e PF is aaaa:bb.cc, the number of reserved queues per
  VF can be configured with EAL parameter like -w aaaa:bb.cc,queue-num-per-vf=n.
  The value n can be 1, 2, 4, 8 or 16. If no such parameter is configured, the
  number of reserved queues per VF is 4 by default. If VF request more than
  reserved queues per VF, PF will able to allocate max to 16 queues after a VF
  reset.


- ``Support multiple driver`` (default ``disable``)

  There was a multiple driver support issue during use of 700 series Ethernet
  Adapter with both Linux kernel and DPDK PMD. To fix this issue, ``devargs``
  parameter ``support-multi-driver`` is introduced, for example::

    -w 84:00.0,support-multi-driver=1

  With the above configuration, DPDK PMD will not change global registers, and
  will switch PF interrupt from IntN to Int0 to avoid interrupt conflict between
  DPDK and Linux Kernel.

- ``Support VF Port Representor`` (default ``not enabled``)

  The i40e PF PMD supports the creation of VF port representors for the control
  and monitoring of i40e virtual function devices. Each port representor
  corresponds to a single virtual function of that device. Using the ``devargs``
  option ``representor`` the user can specify which virtual functions to create
  port representors for on initialization of the PF PMD by passing the VF IDs of
  the VFs which are required.::

  -w DBDF,representor=[0,1,4]

  Currently hot-plugging of representor ports is not supported so all required
  representors must be specified on the creation of the PF.

- ``Use latest supported vector`` (default ``disable``)

  Latest supported vector path may not always get the best perf so vector path was
  recommended to use only on later platform. But users may want the latest vector path
  since it can get better perf in some real work loading cases. So ``devargs`` param
  ``use-latest-supported-vec`` is introduced, for example::

  -w 84:00.0,use-latest-supported-vec=1

Vector RX 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``.

Driver compilation and testing
------------------------------

Refer to the document :ref:`compiling and testing a PMD for a NIC <pmd_build_and_test>`
for details.


SR-IOV: Prerequisites and sample Application Notes
--------------------------------------------------

#. Load the kernel module:

   .. code-block:: console

      modprobe i40e

   Check the output in dmesg:

   .. code-block:: console

      i40e 0000:83:00.1 ens802f0: renamed from eth0

#. Bring up the PF ports:

   .. code-block:: console

      ifconfig ens802f0 up

#. Create VF device(s):

   Echo the number of VFs to be created into the ``sriov_numvfs`` sysfs entry
   of the parent PF.

   Example:

   .. code-block:: console

      echo 2 > /sys/devices/pci0000:00/0000:00:03.0/0000:81:00.0/sriov_numvfs


#. Assign VF MAC address:

   Assign MAC address to the VF using iproute2 utility. The syntax is:

   .. code-block:: console

      ip link set <PF netdev id> vf <VF id> mac <macaddr>

   Example:

   .. code-block:: console

      ip link set ens802f0 vf 0 mac a0:b0:c0:d0:e0:f0

#. Assign VF to VM, and bring up the VM.
   Please see the documentation for the *I40E/IXGBE/IGB Virtual Function Driver*.

#. Running testpmd:

   Follow instructions available in the document
   :ref:`compiling and testing a PMD for a NIC <pmd_build_and_test>`
   to run testpmd.

   Example output:

   .. code-block:: console

      ...
      EAL: PCI device 0000:83:00.0 on NUMA socket 1
      EAL: probe driver: 8086:1572 rte_i40e_pmd
      EAL: PCI memory mapped at 0x7f7f80000000
      EAL: PCI memory mapped at 0x7f7f80800000
      PMD: eth_i40e_dev_init(): FW 5.0 API 1.5 NVM 05.00.02 eetrack 8000208a
      Interactive-mode selected
      Configuring Port 0 (socket 0)
      ...

      PMD: i40e_dev_rx_queue_setup(): Rx Burst Bulk Alloc Preconditions are
      satisfied.Rx Burst Bulk Alloc function will be used on port=0, queue=0.

      ...
      Port 0: 68:05:CA:26:85:84
      Checking link statuses...
      Port 0 Link Up - speed 10000 Mbps - full-duplex
      Done

      testpmd>


Sample Application Notes
------------------------

Vlan filter
~~~~~~~~~~~

Vlan filter only works when Promiscuous mode is off.

To start ``testpmd``, and add vlan 10 to port 0:

.. code-block:: console

    ./app/testpmd -l 0-15 -n 4 -- -i --forward-mode=mac
    ...

    testpmd> set promisc 0 off
    testpmd> rx_vlan add 10 0


Flow Director
~~~~~~~~~~~~~

The Flow Director works in receive mode to identify specific flows or sets of flows and route them to specific queues.
The Flow Director filters can match the different fields for different type of packet: flow type, specific input set per flow type and the flexible payload.

The default input set of each flow type is::

   ipv4-other : src_ip_address, dst_ip_address
   ipv4-frag  : src_ip_address, dst_ip_address
   ipv4-tcp   : src_ip_address, dst_ip_address, src_port, dst_port
   ipv4-udp   : src_ip_address, dst_ip_address, src_port, dst_port
   ipv4-sctp  : src_ip_address, dst_ip_address, src_port, dst_port,
                verification_tag
   ipv6-other : src_ip_address, dst_ip_address
   ipv6-frag  : src_ip_address, dst_ip_address
   ipv6-tcp   : src_ip_address, dst_ip_address, src_port, dst_port
   ipv6-udp   : src_ip_address, dst_ip_address, src_port, dst_port
   ipv6-sctp  : src_ip_address, dst_ip_address, src_port, dst_port,
                verification_tag
   l2_payload : ether_type

The flex payload is selected from offset 0 to 15 of packet's payload by default, while it is masked out from matching.

Start ``testpmd`` with ``--disable-rss`` and ``--pkt-filter-mode=perfect``:

.. code-block:: console

   ./app/testpmd -l 0-15 -n 4 -- -i --disable-rss --pkt-filter-mode=perfect \
                 --rxq=8 --txq=8 --nb-cores=8 --nb-ports=1

Add a rule to direct ``ipv4-udp`` packet whose ``dst_ip=2.2.2.5, src_ip=2.2.2.3, src_port=32, dst_port=32`` to queue 1:

.. code-block:: console

   testpmd> flow_director_filter 0 mode IP add flow ipv4-udp  \
            src 2.2.2.3 32 dst 2.2.2.5 32 vlan 0 flexbytes () \
	    fwd pf queue 1 fd_id 1

Check the flow director status:

.. code-block:: console

   testpmd> show port fdir 0

   ######################## FDIR infos for port 0      ####################
     MODE:   PERFECT
     SUPPORTED FLOW TYPE:  ipv4-frag ipv4-tcp ipv4-udp ipv4-sctp ipv4-other
                           ipv6-frag ipv6-tcp ipv6-udp ipv6-sctp ipv6-other
			   l2_payload
     FLEX PAYLOAD INFO:
     max_len:	    16	        payload_limit: 480
     payload_unit:  2	        payload_seg:   3
     bitmask_unit:  2	        bitmask_num:   2
     MASK:
       vlan_tci: 0x0000,
       src_ipv4: 0x00000000,
       dst_ipv4: 0x00000000,
       src_port: 0x0000,
       dst_port: 0x0000
       src_ipv6: 0x00000000,0x00000000,0x00000000,0x00000000,
       dst_ipv6: 0x00000000,0x00000000,0x00000000,0x00000000
     FLEX PAYLOAD SRC OFFSET:
       L2_PAYLOAD:    0      1	    2	   3	  4	 5	6  ...
       L3_PAYLOAD:    0      1	    2	   3	  4	 5	6  ...
       L4_PAYLOAD:    0      1	    2	   3	  4	 5	6  ...
     FLEX MASK CFG:
       ipv4-udp:    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv4-tcp:    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv4-sctp:   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv4-other:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv4-frag:   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv6-udp:    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv6-tcp:    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv6-sctp:   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv6-other:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       ipv6-frag:   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
       l2_payload:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     guarant_count: 1	        best_count:    0
     guarant_space: 512         best_space:    7168
     collision:     0	        free:	       0
     maxhash:	    0	        maxlen:        0
     add:	    0	        remove:        0
     f_add:	    0	        f_remove:      0


Delete all flow director rules on a port:

.. code-block:: console

   testpmd> flush_flow_director 0

Floating VEB
~~~~~~~~~~~~~

The Intel® Ethernet 700 Series support a feature called
"Floating VEB".

A Virtual Ethernet Bridge (VEB) is an IEEE Edge Virtual Bridging (EVB) term
for functionality that allows local switching between virtual endpoints within
a physical endpoint and also with an external bridge/network.

A "Floating" VEB doesn't have an uplink connection to the outside world so all
switching is done internally and remains within the host. As such, this
feature provides security benefits.

In addition, a Floating VEB overcomes a limitation of normal VEBs where they
cannot forward packets when the physical link is down. Floating VEBs don't need
to connect to the NIC port so they can still forward traffic from VF to VF
even when the physical link is down.

Therefore, with this feature enabled VFs can be limited to communicating with
each other but not an outside network, and they can do so even when there is
no physical uplink on the associated NIC port.

To enable this feature, the user should pass a ``devargs`` parameter to the
EAL, for example::

    -w 84:00.0,enable_floating_veb=1

In this configuration the PMD will use the floating VEB feature for all the
VFs created by this PF device.

Alternatively, the user can specify which VFs need to connect to this floating
VEB using the ``floating_veb_list`` argument::

    -w 84:00.0,enable_floating_veb=1,floating_veb_list=1;3-4

In this example ``VF1``, ``VF3`` and ``VF4`` connect to the floating VEB,
while other VFs connect to the normal VEB.

The current implementation only supports one floating VEB and one regular
VEB. VFs can connect to a floating VEB or a regular VEB according to the
configuration passed on the EAL command line.

The floating VEB functionality requires a NIC firmware version of 5.0
or greater.

Dynamic Device Personalization (DDP)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Intel® Ethernet 700 Series except for the Intel Ethernet Connection
X722 support a feature called "Dynamic Device Personalization (DDP)",
which is used to configure hardware by downloading a profile to support
protocols/filters which are not supported by default. The DDP
functionality requires a NIC firmware version of 6.0 or greater.

Current implementation supports GTP-C/GTP-U/PPPoE/PPPoL2TP,
steering can be used with rte_flow API.

GTPv1 package is released, and it can be downloaded from
https://downloadcenter.intel.com/download/27587.

PPPoE package is released, and it can be downloaded from
https://downloadcenter.intel.com/download/28040.

Load a profile which supports GTP and store backup profile:

.. code-block:: console

   testpmd> ddp add 0 ./gtp.pkgo,./backup.pkgo

Delete a GTP profile and restore backup profile:

.. code-block:: console

   testpmd> ddp del 0 ./backup.pkgo

Get loaded DDP package info list:

.. code-block:: console

   testpmd> ddp get list 0

Display information about a GTP profile:

.. code-block:: console

   testpmd> ddp get info ./gtp.pkgo

Input set configuration
~~~~~~~~~~~~~~~~~~~~~~~
Input set for any PCTYPE can be configured with user defined configuration,
For example, to use only 48bit prefix for IPv6 src address for IPv6 TCP RSS:

.. code-block:: console

   testpmd> port config 0 pctype 43 hash_inset clear all
   testpmd> port config 0 pctype 43 hash_inset set field 13
   testpmd> port config 0 pctype 43 hash_inset set field 14
   testpmd> port config 0 pctype 43 hash_inset set field 15

Queue region configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Intel® Ethernet 700 Series supports a feature of queue regions
configuration for RSS in the PF, so that different traffic classes or
different packet classification types can be separated to different
queues in different queue regions. There is an API for configuration
of queue regions in RSS with a command line. It can parse the parameters
of the region index, queue number, queue start index, user priority, traffic
classes and so on. Depending on commands from the command line, it will call
i40e private APIs and start the process of setting or flushing the queue
region configuration. As this feature is specific for i40e only private
APIs are used. These new ``test_pmd`` commands are as shown below. For
details please refer to :doc:`../testpmd_app_ug/index`.

.. code-block:: console

   testpmd> set port (port_id) queue-region region_id (value) \
		queue_start_index (value) queue_num (value)
   testpmd> set port (port_id) queue-region region_id (value) flowtype (value)
   testpmd> set port (port_id) queue-region UP (value) region_id (value)
   testpmd> set port (port_id) queue-region flush (on|off)
   testpmd> show port (port_id) queue-region

Limitations or Known issues
---------------------------

MPLS packet classification
~~~~~~~~~~~~~~~~~~~~~~~~~~

For firmware versions prior to 5.0, MPLS packets are not recognized by the NIC.
The L2 Payload flow type in flow director can be used to classify MPLS packet
by using a command in testpmd like:

   testpmd> flow_director_filter 0 mode IP add flow l2_payload ether \
            0x8847 flexbytes () fwd pf queue <N> fd_id <M>

With the NIC firmware version 5.0 or greater, some limited MPLS support
is added: Native MPLS (MPLS in Ethernet) skip is implemented, while no
new packet type, no classification or offload are possible. With this change,
L2 Payload flow type in flow director cannot be used to classify MPLS packet
as with previous firmware versions. Meanwhile, the Ethertype filter can be
used to classify MPLS packet by using a command in testpmd like:

   testpmd> ethertype_filter 0 add mac_ignr 00:00:00:00:00:00 ethertype \
            0x8847 fwd queue <M>

16 Byte RX Descriptor setting on DPDK VF
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Currently the VF's RX descriptor mode is decided by PF. There's no PF-VF
interface for VF to request the RX descriptor mode, also no interface to notify
VF its own RX descriptor mode.
For all available versions of the i40e driver, these drivers don't support 16
byte RX descriptor. If the Linux i40e kernel driver is used as host driver,
while DPDK i40e PMD is used as the VF driver, DPDK cannot choose 16 byte receive
descriptor. The reason is that the RX descriptor is already set to 32 byte by
the i40e kernel driver. That is to say, user should keep
``CONFIG_RTE_LIBRTE_I40E_16BYTE_RX_DESC=n`` in config file.
In the future, if the Linux i40e driver supports 16 byte RX descriptor, user
should make sure the DPDK VF uses the same RX descriptor mode, 16 byte or 32
byte, as the PF driver.

The same rule for DPDK PF + DPDK VF. The PF and VF should use the same RX
descriptor mode. Or the VF RX will not work.

Receive packets with Ethertype 0x88A8
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Due to the FW limitation, PF can receive packets with Ethertype 0x88A8
only when floating VEB is disabled.

Incorrect Rx statistics when packet is oversize
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When a packet is over maximum frame size, the packet is dropped.
However, the Rx statistics, when calling `rte_eth_stats_get` incorrectly
shows it as received.

VF & TC max bandwidth setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The per VF max bandwidth and per TC max bandwidth cannot be enabled in parallel.
The behavior is different when handling per VF and per TC max bandwidth setting.
When enabling per VF max bandwidth, SW will check if per TC max bandwidth is
enabled. If so, return failure.
When enabling per TC max bandwidth, SW will check if per VF max bandwidth
is enabled. If so, disable per VF max bandwidth and continue with per TC max
bandwidth setting.

TC TX scheduling mode setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There are 2 TX scheduling modes for TCs, round robin and strict priority mode.
If a TC is set to strict priority mode, it can consume unlimited bandwidth.
It means if APP has set the max bandwidth for that TC, it comes to no
effect.
It's suggested to set the strict priority mode for a TC that is latency
sensitive but no consuming much bandwidth.

VF performance is impacted by PCI extended tag setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To reach maximum NIC performance in the VF the PCI extended tag must be
enabled. The DPDK i40e PF driver will set this feature during initialization,
but the kernel PF driver does not. So when running traffic on a VF which is
managed by the kernel PF driver, a significant NIC performance downgrade has
been observed (for 64 byte packets, there is about 25% line-rate downgrade for
a 25GbE device and about 35% for a 40GbE device).

For kernel version >= 4.11, the kernel's PCI driver will enable the extended
tag if it detects that the device supports it. So by default, this is not an
issue. For kernels <= 4.11 or when the PCI extended tag is disabled it can be
enabled using the steps below.

#. Get the current value of the PCI configure register::

      setpci -s <XX:XX.X> a8.w

#. Set bit 8::

      value = value | 0x100

#. Set the PCI configure register with new value::

      setpci -s <XX:XX.X> a8.w=<value>

Vlan strip of VF
~~~~~~~~~~~~~~~~

The VF vlan strip function is only supported in the i40e kernel driver >= 2.1.26.

DCB function
~~~~~~~~~~~~

DCB works only when RSS is enabled.

Global configuration warning
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I40E PMD will set some global registers to enable some function or set some
configure. Then when using different ports of the same NIC with Linux kernel
and DPDK, the port with Linux kernel will be impacted by the port with DPDK.
For example, register I40E_GL_SWT_L2TAGCTRL is used to control L2 tag, i40e
PMD uses I40E_GL_SWT_L2TAGCTRL to set vlan TPID. If setting TPID in port A
with DPDK, then the configuration will also impact port B in the NIC with
kernel driver, which don't want to use the TPID.
So PMD reports warning to clarify what is changed by writing global register.

High Performance of Small Packets on 40GbE NIC
----------------------------------------------

As there might be firmware fixes for performance enhancement in latest version
of firmware image, the firmware update might be needed for getting high performance.
Check the Intel support website for the latest firmware updates.
Users should consult the release notes specific to a DPDK release to identify
the validated firmware version for a NIC using the i40e driver.

Use 16 Bytes RX Descriptor Size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As i40e PMD supports both 16 and 32 bytes RX descriptor sizes, and 16 bytes size can provide helps to high performance of small packets.
Configuration of ``CONFIG_RTE_LIBRTE_I40E_16BYTE_RX_DESC`` in config files can be changed to use 16 bytes size RX descriptors.

Example of getting best performance with l3fwd example
------------------------------------------------------

The following is an example of running the DPDK ``l3fwd`` sample application to get high performance with a
server with Intel Xeon processors and Intel Ethernet CNA XL710.

The example scenario is to get best performance with two Intel Ethernet CNA XL710 40GbE ports.
See :numref:`figure_intel_perf_test_setup` for the performance test setup.

.. _figure_intel_perf_test_setup:

.. figure:: img/intel_perf_test_setup.*

   Performance Test Setup


1. Add two Intel Ethernet CNA XL710 to the platform, and use one port per card to get best performance.
   The reason for using two NICs is to overcome a PCIe v3.0 limitation since it cannot provide 80GbE bandwidth
   for two 40GbE ports, but two different PCIe v3.0 x8 slot can.
   Refer to the sample NICs output above, then we can select ``82:00.0`` and ``85:00.0`` as test ports::

      82:00.0 Ethernet [0200]: Intel XL710 for 40GbE QSFP+ [8086:1583]
      85:00.0 Ethernet [0200]: Intel XL710 for 40GbE QSFP+ [8086:1583]

2. Connect the ports to the traffic generator. For high speed testing, it's best to use a hardware traffic generator.

3. Check the PCI devices numa node (socket id) and get the cores number on the exact socket id.
   In this case, ``82:00.0`` and ``85:00.0`` are both in socket 1, and the cores on socket 1 in the referenced platform
   are 18-35 and 54-71.
   Note: Don't use 2 logical cores on the same core (e.g core18 has 2 logical cores, core18 and core54), instead, use 2 logical
   cores from different cores (e.g core18 and core19).

4. Bind these two ports to igb_uio.

5. As to Intel Ethernet CNA XL710 40GbE port, we need at least two queue pairs to achieve best performance, then two queues per port
   will be required, and each queue pair will need a dedicated CPU core for receiving/transmitting packets.

6. The DPDK sample application ``l3fwd`` will be used for performance testing, with using two ports for bi-directional forwarding.
   Compile the ``l3fwd sample`` with the default lpm mode.

7. The command line of running l3fwd would be something like the following::

      ./l3fwd -l 18-21 -n 4 -w 82:00.0 -w 85:00.0 \
              -- -p 0x3 --config '(0,0,18),(0,1,19),(1,0,20),(1,1,21)'

   This means that the application uses core 18 for port 0, queue pair 0 forwarding, core 19 for port 0, queue pair 1 forwarding,
   core 20 for port 1, queue pair 0 forwarding, and core 21 for port 1, queue pair 1 forwarding.

8. Configure the traffic at a traffic generator.

   * Start creating a stream on packet generator.

   * Set the Ethernet II type to 0x0800.

Tx bytes affected by the link status change
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For firmware versions prior to 6.01 for X710 series and 3.33 for X722 series, the tx_bytes statistics data is affected by
the link down event. Each time the link status changes to down, the tx_bytes decreases 110 bytes.