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

[Bruce Richardson <bruce.richardson@intel.com>]

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?

> So, the best option is to let packets carry a flag in mbuf to tell drive in fast path. 
> You can see that this is unique to fm10k and we thought community won't like to see 
> this flag introduced into mbuf. If you do agree, we can introduce a new flag.

Why does it need to be specified per-mbuf? The existing config flag added is
global, so a per-mbuf flag shouldn't be needed to get equivalent behaviour.

> So, we step backwards and assume customer will use static configurations to enable
> this feature. After it is enabled, we'll assume app will use FTAG for all packets.

Yes, but instead of compile time option, why not port config-time option instead?

/Bruce