Re: [dpdk-dev] [PATCH v3 1/3] fm10k: enable FTAG based forwarding

["Wang, Xiao W" <xiao.w.wang@intel.com>]

Hi,

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Friday, February 26, 2016 12:14 AM
> To: Chen, Jing D <jing.d.chen@intel.com>
> Cc: Thomas Monjalon <thomas.monjalon@6wind.com>; Wang, Xiao W
> <xiao.w.wang@intel.com>; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v3 1/3] fm10k: enable FTAG based forwarding
> 
> On Thu, Feb 25, 2016 at 03:45:45PM +0000, Chen, Jing D wrote:
> > Hi, Bruce,
> >
> > > -----Original Message-----
> > > From: Richardson, Bruce
> > > Sent: Thursday, February 25, 2016 9:35 PM
> > > To: Chen, Jing D <jing.d.chen@intel.com>
> > > Cc: Thomas Monjalon <thomas.monjalon@6wind.com>; Wang, Xiao W
> > > <xiao.w.wang@intel.com>; dev@dpdk.org
> > > Subject: Re: [dpdk-dev] [PATCH v3 1/3] fm10k: enable FTAG based
> > > forwarding
> > >
> > > On Thu, Feb 25, 2016 at 10:04:02AM +0000, Chen, Jing D wrote:
> > > > Hi, Bruce, Thomas,
> > > >
> > > > Best Regards,
> > > > Mark
> > > >
> > > > > -----Original Message-----
> > > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas
> > > Monjalon
> > > > > Sent: Thursday, February 25, 2016 12:38 AM
> > > > > To: Richardson, Bruce; Wang, Xiao W
> > > > > Cc: dev@dpdk.org
> > > > > Subject: Re: [dpdk-dev] [PATCH v3 1/3] fm10k: enable FTAG based
> > > > > forwarding
> > > > >
> > > > > 2016-02-24 15:42, Bruce Richardson:
> > > > > > On Thu, Feb 04, 2016 at 11:38:47AM +0800, Wang Xiao W wrote:
> > > > > > > This patch enables reading sglort info into mbuf for RX and
> > > > > > > inserting an FTAG at the beginning of the packet for TX. The
> > > > > > > vlan_tci_outer field selected from rte_mbuf structure for
> > > > > > > sglort is not
> > > used in fm10k now.
> > > > > > > In FTAG based forwarding mode, the switch will forward
> > > > > > > packets
> > > > > according
> > > > > > > to glort info in FTAG rather than mac and vlan table.
> > > > > > >
> > > > > > > To activate this feature, user needs to turn
> > > > > ``CONFIG_RTE_LIBRTE_FM10K_FTAG_FWD``
> > > > > > > to y in common_linuxapp or common_bsdapp. Currently this
> > > > > > > feature is
> > > > > supported
> > > > > > > only on PF, because FM10K_PFVTCTL register is read-only for VF.
> > > > > > >
> > > > > > > Signed-off-by: Wang Xiao W <xiao.w.wang@intel.com>
> > > > > >
> > > > > > Any comments on this patch?
> > > > > >
> > > > > > My thoughts: is there a way in which this could be done
> > > > > > without adding in a
> > > > > new
> > > > > > build time config option?
> > > > >
> > > > > Bruce, it's simpler to explain that build time options are
> > > > > forbidden to enable such options.
> > > > > Or the terrific kid's approach: one day, the Big Build-Option
> > > > > Eater will come and will eat every undecided features! ;)
> > > >
> > > > This feature is trying to use FTAG (a unique tech in fm10k)
> > > > instead of mac/vlan to forward packets. App need a way to tell PMD
> > > > driver that which forwarding style it would like to use.
> > >
> > > Why not just specify this in the port configuration at setup time?
> > >
> >
> > Please educate me. I think the port configuration flags are also
> > common to all PMD Drivers. Is it possible to add a flag like "RTE_USE_FTAG"
> and pass to PMD driver?
> >
> They are.
> For something PMD specific, like FTAG, it's always a challenge, and I don't
> know off the top of my head if there is a simple option. However, given the
> choice between an mbuf flag and a port config flag, I'd always choose the
> former.
> Other alternatives would be to have a fm10k specific API in the fm10k driver
> alone.
> 
> I'll let Thomas as ethdev maintainer comment if he has other suggestions as to
> how to handle this case. I suspect this won't be the first device-specific piece of
> functionality we need to deal with.
> 
> /Bruce

Whatever method we choose, we have to find a way for the user to express his need
for FTAG, it maybe a build time config option, or a port config flag (no such flag now),
or a fast path flag in mbuf (no such flag now) etc. For the customer Topsec's use case,
they use FTAG for all the TX packets, so all the above methods (per build config, per
port config, per mbuf config) can meet their need. Since the pmd frame work is for
common, it's hard to add new fields only for one specific NIC, so I add a build time
config and make an introduction in the doc.

Thanks for the discussion, Thomas, do you have any suggestions?

BTW, I have found the patch needs to be rebased on head of dpdk-next-net/rel_16_04 since several
fm10k patches were applied recently.

Best Regards,
Xiao