[dpdk-dev] [PATCH v5 2/3] lib/gro: add TCP/IPv4 GRO support

[Tan, Jianfeng]

Hi Jiayu,

> -----Original Message-----
> From: Hu, Jiayu
> Sent: Thursday, June 22, 2017 4:18 PM
> To: Tan, Jianfeng
> Cc: dev at dpdk.org; Ananyev, Konstantin; yliu at fridaylinux.org; Wiles, Keith;
> Bie, Tiwei; Yao, Lei A
> Subject: Re: [PATCH v5 2/3] lib/gro: add TCP/IPv4 GRO support
> 
> On Mon, Jun 19, 2017 at 11:43:20PM +0800, Tan, Jianfeng wrote:
> >
> >
> > On 6/18/2017 3:21 PM, Jiayu Hu wrote:
> > >
> > > Each element in the flow array records the information of one flow,
> > > which includes two parts:
> > > - key: the criteria of the same flow. If packets have the same key
> > >      value, they belong to the same flow.
> > > - start_index: the index of the first incoming packet of this flow in
> > >      the item array. With start_index, we can locate the first incoming
> > >      packet of this flow.
> > > Each element in the item array records one packet information. It mainly
> > > includes two parts:
> > > - pkt: packet address
> > > - next_pkt_index: index of the next packet of the same flow in the item
> > >      array. All packets of the same flow are chained by next_pkt_index.
> > >      With next_pkt_index, we can locate all packets of the same flow
> > >      one by one.
> > >
> > > To process an incoming packet, we need three steps:
> > > a. check if the packet should be processed. Packets with the following
> > >      properties won't be processed:
> > > 	- packets without data;
> > > 	- packets with wrong checksums;
> >
> > Why do we care to check this kind of error? Can we just suppose the
> > applications have already dropped the packets with wrong cksum?
> >
> > > 	- fragmented packets.
> >
> > IP fragmented? I don't think we need to check it here either. It's the
> > application's responsibility to call librte_ip_frag firstly to reassemble
> > IP-fragmented packets, and then call this gro library to merge TCP packets.
> > And this procedure should be shown in an example for other users to refer.
> 
> If we leave this check to applications, they have to call librte_ip_frag
> first, then call GRO library. If they call GRO library first, error
> happens. But if GRO checks if the packet is fragmented, no error happens.
> IMO, it's more flexible. Besides, for GRO library, to check if the packet
> is fragmented is very simple. Just to check if DF bit is set is enough.
> So I still think GRO library need to check it.

I would expect ip fragment is also a gro engine (might be two for ipv4 and ipv6).