[dpdk-dev] [PATCH v2] doc: more clarification for i40e 16 bytes desc

[Lu, Wenzhuo]

Hi Bruce,


> -----Original Message-----
> From: Richardson, Bruce
> Sent: Tuesday, October 31, 2017 6:04 PM
> To: Lu, Wenzhuo <wenzhuo.lu at intel.com>
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] doc: more clarification for i40e 16 bytes
> desc
> 
> On Tue, Oct 31, 2017 at 11:40:33AM +0800, Wenzhuo Lu wrote:
> > The description of i40e 16 bytes descriptor is not clear enough. Add
> > more details.
> >
> > Signed-off-by: Wenzhuo Lu <wenzhuo.lu at intel.com>
> 
> Thanks for the clarification, it's better now. Couple of minor tweaks I would
> suggest below.
> 
> Otherwise:
> Acked-by: Bruce Richardson <bruce.richardson at intel.com>
> 
> > ---
> >  doc/guides/nics/i40e.rst | 21 ++++++++++++++++-----
> >  1 file changed, 16 insertions(+), 5 deletions(-)
> >
> > diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst index
> > a0946e6..771620c 100644
> > --- a/doc/guides/nics/i40e.rst
> > +++ b/doc/guides/nics/i40e.rst
> > @@ -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 Bytes Descriptor setting on DPDK VF
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> We tend to refer to these as "16-byte" and "32-byte" descriptors in the
> singular, not "16-bytes".
> 
> >
> > +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 nofify VF its own RX descriptor mode.
> > +Until i40e 2.1.26, the Linux i40e driver doesn't support 16 bytes RX
> descriptor.
> 
> This implies that the 2.1.26 driver does support setting the descriptor size,
> though later text implies that this is not the case.
> Therefore, I suggest changing "Until i40e 2.1.26", to "For all available
> versions of the i40e driver," and omit the version number, since it will soon
> be out of date otherwise. The only time we should need to update this is
> when/if there is a kernel version that does support reporting or seting the
> descriptor size.
Thanks for the review and comments. I'll send a V3 and add your ack :)

> 
> >  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.
> > +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
> > +bytes 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 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
> >