Re: [GRO] check whether ip_id continuity needs to be checked when two TCP packets are merged.

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 20 Apr 2023 02:30:41 +0000
"Hu, Jiayu" <jiayu.hu@intel.com> wrote:

> Hi Cheng,
> 
> > -----Original Message-----
> > From: jiangheng (G) <jiangheng14@huawei.com>
> > Sent: Saturday, April 15, 2023 10:46 PM
> > To: users@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; dev@dpdk.org
> > Subject: [GRO] check whether ip_id continuity needs to be checked when
> > two TCP packets are merged.
> > 
> > Hi jiayu.hu
> > 
> > It cannot be guaranteed that 16bit identification field of ip packets in the
> > same tcp stream will be continuous.
> > Please help check whether ip_id continuity needs to be checked when two
> > TCP packets are merged?
> > Seems to modify the following code, gro will aggregate better, and work
> > better:
> > 
> > diff --git a/lib/gro/gro_tcp4.h b/lib/gro/gro_tcp4.h index
> > 212f97a042..06faead7b5 100644
> > --- a/lib/gro/gro_tcp4.h
> > +++ b/lib/gro/gro_tcp4.h
> > @@ -291,12 +291,10 @@ check_seq_option(struct gro_tcp4_item *item,
> >         /* check if the two packets are neighbors */
> >         len = pkt_orig->pkt_len - l2_offset - pkt_orig->l2_len -
> >                 pkt_orig->l3_len - tcp_hl_orig;
> > -       if ((sent_seq == item->sent_seq + len) && (is_atomic ||
> > -                               (ip_id == item->ip_id + 1)))
> > +       if (sent_seq == item->sent_seq + len)  
> 
> For atomic packets, the IP ID field is ignored, as it can be set in various ways.
> For non-atomic packets, it follows Linux kernel tcp_gro_receive().
> 
> Is this change specific to your case? Can you give more details on why it helps?
> 
> Thanks,
> Jiayu

Agreed, DPDK GRO should follow Linux to avoid bugs.