Hi Bruce, > -----Original Message----- > From: Richardson, Bruce > Sent: Wednesday, October 25, 2017 4:37 PM > To: Lu, Wenzhuo <wenzhuo...@intel.com> > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH] doc: more clarification for i40e 16 bytes desc > > On Wed, Oct 25, 2017 at 10:54:53AM +0800, Wenzhuo Lu wrote: > > The description of i40e 16 bytes descriptor is not clear enough. Add > > more details. > > > > Signed-off-by: Wenzhuo Lu <wenzhuo...@intel.com> > > --- > > Good idea to document this better. > > > doc/guides/nics/i40e.rst | 11 +++++++++-- > > 1 file changed, 9 insertions(+), 2 deletions(-) > > > > diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst index > > a0946e6..e0237a8 100644 > > --- a/doc/guides/nics/i40e.rst > > +++ b/doc/guides/nics/i40e.rst > > @@ -398,13 +398,20 @@ 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 Bytes Descriptor setting on DPDK VF > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > +Until 2.1.26, the Linux i40e driver doesn't support 16 bytes RX descriptor. > > I assume that 2.1.26 is referring to the i40e driver version, not the linux > kernel version. This should be made clearer, as it also could be read as a > very > old kernel version. OK, I'll change it to i40e 2.1.26.
> > > 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. > > Can you explain - either on-list here, or actually in the docs - why there is > this restriction? Is it HW or SW? A reference to the section in the datasheet > for it would also be good. For example Table 8-10 in the datasheet lists no > restriction on the Dsize bit in the queue context. It's not a HW limitation. To my opinion, it's SW design and implementation limitation. I'll add more details. > > > +In the future, if the Linux i40e driver supports 16 bytes RX > > +descriptor, user should make sure the DPDK VF uses the same RX > > +descriptor mode, 16 bytes or 32 bytes, 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 > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > -- > > 1.9.3 > > > > > Regards, > /Bruce
