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doc: add clarification for i40e 16 byte desc

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The description of i40e 16 byte descriptor is not clear
enough. Add more details.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
This commit is contained in:
Wenzhuo Lu 2017-11-01 10:45:28 +08:00 committed by Ferruh Yigit
parent f8879d22bc
commit 8c22b59a17
1 changed files with 17 additions and 6 deletions
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23
doc/guides/nics/i40e.rst
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@ -398,13 +398,24 @@ 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 Descriptor cannot be used on DPDK VF
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
16 Byte RX Descriptor setting on DPDK VF
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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. That
is to say, user should keep ``CONFIG_RTE_LIBRTE_I40E_16BYTE_RX_DESC=n`` in
config file.
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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~