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

["Chen, Jing D" <jing.d.chen@intel.com>]

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?

> > 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