[dpdk-dev] [PATCH 0/2] lib: add TCP IPv4 GRO support

[Ananyev, Konstantin]

> -----Original Message-----
> From: Hu, Jiayu
> Sent: Friday, March 24, 2017 8:07 AM
> To: Yuanhan Liu <yuanhan.liu at linux.intel.com>
> Cc: Wiles, Keith <keith.wiles at intel.com>; Ananyev, Konstantin <konstantin.ananyev at intel.com>; Richardson, Bruce
> <bruce.richardson at intel.com>; Stephen Hemminger <stephen at networkplumber.org>; Yigit, Ferruh <ferruh.yigit at intel.com>;
> dev at dpdk.org; Liang, Cunming <cunming.liang at intel.com>; Thomas Monjalon <thomas.monjalon at 6wind.com>
> Subject: Re: [dpdk-dev] [PATCH 0/2] lib: add TCP IPv4 GRO support
> 
> On Fri, Mar 24, 2017 at 03:22:30PM +0800, Yuanhan Liu wrote:
> > On Fri, Mar 24, 2017 at 06:18:48AM +0000, Wiles, Keith wrote:
> > > >> I think that having a separate library for GRO is a step in a right direction.
> > > >>> From my perspective - it provides a clean and flexible way to use that feature.
> > > >> If later someone would like to put GRO into ethdev layer (or particular PMD),
> > > >> he can use existing librte_gro for that.
> > > >
> > > > Agree. I think introducing more flexibility is an important thing for applications.
> > >
> > > Creating a new library just for GRO is not a reasonable solution, but adding that support to an existing library like librte_net would
> be cleaner and not create yet another library.
> >
> > Librte_net seems like a good suggestion to me, especially when we are
> > considering to add GSO in future. The only concern to me is "net" may
> > be too generic. It maybe kind of hard to decide which should be in
> > librte_net, and which should be added as a standalone lib. For example,
> > shouldn't 'lpm' and 'ip_frag' also belong to librte_net?

About librte_gro vs librte_net:

Right now librte_net is quite lightweight one - it mostly contains a net protocols definitions
plus some extra helper functions: to parse the l2/l3 headers to determine ptype, to calculate cksum, etc.
GRO code is quite different - it has to allocate and manage hash table(s), etc.
Again my understanding it would keep growing (with new proto support).
Again as mentioned above if GRO should go into librte_net, then librte_ipfrag and future GSO should also be here.
Which would create quite a monstrous library.  
So I think it is better to keep librte_net small and tidy and put GRO functionality into the new library.

> >
> > > Creating more flexibility is not the best goal as we really want to make GRO easy and simple for the developer to use for any
> device without having to change his applications to take advantage of the feature. Some times providing more flexibility just means
> making it more complexed and more APIs the developer needs to understand. Providing GRO as a offload feature is the better
> direction as it makes it simple for an application to use.
> > >
> > > If we provide GRO as a standard offload similar to the other offloads we currently have makes it easy for the developer. The best
> goal for a feature is the best performance for the application without having the application make even more APIs calls along with
> simple and easy to use.
> >
> > In general, I'd agree with you, if no one is object to add a short piece
> > of code at the end of rte_eth_rx_burst:
> >
> >      +       if (eth_gro_is_enabled(dev))
> >      +               nb_rx = rte_net_gro(...);
> >      +
> >              return nb_rx;
> >       }
> >
> > Objections?

I'd better not to open that door.
If we'll allow that for GRO - we'll have to allow that for every other stuff:
- ip reassembly
- l3/l4 cksum calculation if underlying HW doesn't support it
- SW ptype recognition
- etc.

Adding all these things into rx_burst() would most likely slow things down
(remember it is a data-path) and pretty soon would bring rx_burst() into
messy monster that would be hard to maintain and debug.    

My preference would be to keep rte_ethdev data-path as small and tidy as possible.
If in future we'd really like to introduce all these SW things into dev layer -
my preference would be to create some sort of new abstraction on top of current ethdev:
rte_eth_smartdev or so.
So it would be:
rte_eth_smartdev_rx_burst(....)
{
   nb_rx =  rte_eth_rx_burst(...);
   /* apply GRO, reassembly, etc. */
  ...
} 

Something similar with what 6Wind trying to introduce with their failsafe dev concept.

> >
> > But one way or another, we need put the gro code at somewhere and we
> > need introduce a generic API for that. It could be librte_net as you
> > suggested. So the good thing is that we all at least come an agreement
> > that it should be implemented in lib, right? The only controversy is
> > should we export it to application and let them to invoke it, or hide
> > it inside rte_eth_rx_burst.
> >
> > Though it may take some time for all of us to come an agreement on that,
> > but the good thing is that it would be a very trivial change once it's
> > done. Agree?
> 
> Agree.
> 
> >
> > Thus I'd suggest Jiayu to focus on the the GRO code developement, such
> > as making it generic enough and adding other protocols support. And I
> > would like to ask you guys to help review them. Makes sense to all?
> >
> 
> Agree again. No matter where to put GRO code, the apis should be generic
> and extensible. And more protocols should be supported.

Yep, that's what my take from the beginning:
Let's develop a librte_gro first and make it successful, then we can think should
we (and how) put into ethdev layer.

Konstantin

> 
> Thanks,
> Jiayu
> 
> > Thanks.
> >
> > 	--yliu
> >
> >
> > > >> I didn't  have a closer look yet, but I think that caught my attention:
> > > >> API fir the lib seems too IPv4/TCP oriented -
> > > >> though I understand that the most common case and should be implemented first.
> > > >> I wonder can we have it a bit more generic and extendable, so user can specify what combination of protocols
> > > >> he is interested in (let say: ipv4/tcp,  ipv6/tcp, etc.).
> > > >> Even if right now we'll have it implemented only for ipv4/tcp.
> > > >> Then internally we can have some check is that supported or not and if yes setup things accordingly.
> > > >
> > > > Indeed, current apis are too specific. It's not very friendly to applications.
> > > > Maybe we can use macro to define the combination of protocols, like GRO_TCP_IPV4
> > > > and GRO_UDP_IPV6; and provide a generic setup function and reassembly function.
> > > > Both of them perform different operations according to the macro value inputted
> > > > by the application.
> > > >
> > > >> BTW, that's for 17.08, right?
> > > >
> > > > Yes, it's for 17.08.
> > > >
> > > > Jiayu
> > > >>
> > > >> Konstantin
> > > >>
> > > >>
> > >
> > > Regards,
> > > Keith