From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ilya Matveychikov <matvejchikov@gmail.com>
Subject: Re: A question about GRO neighbor packet matching
Date: Wed, 6 Dec 2017 22:38:12 +0400
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 <20171206101200.031afa39@shemminger-XPS-13-9360>
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 jiayu.hu@intel.com
To: Stephen Hemminger <stephen@networkplumber.org>
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> On Dec 6, 2017, at 10:12 PM, Stephen Hemminger =
<stephen@networkplumber.org> wrote:
>=20
> On Wed, 6 Dec 2017 18:02:21 +0400
> Ilya Matveychikov <matvejchikov@gmail.com> wrote:
>=20
>> Hello all,
>>=20
>>=20
>> My question is about neighbor packet matching algorithm for TCP. Is =
it
>> correct to expect that IP packets should have continuous ID =
enumeration
>> (i.e. iph-next.id =3D iph-prev.id + 1)?
>=20
>=20
> No.
>=20
>> ~~~
>> lib/librte_gro/gro_tcp4.c:check_seq_option()
>> 	...
>> 	/* check if the two packets are neighbors */
>> 	tcp_dl0 =3D pkt0->pkt_len - pkt0->l2_len - pkt0->l3_len - =
tcp_hl0;
>> 	if ((sent_seq =3D=3D (item->sent_seq + tcp_dl0)) &&
>> 			(ip_id =3D=3D (item->ip_id + 1)))
>> 		/* append the new packet */
>> 		return 1;
>> 	else if (((sent_seq + tcp_dl) =3D=3D item->sent_seq) &&
>> 			((ip_id + item->nb_merged) =3D=3D item->ip_id))
>> 		/* pre-pend the new packet */
>> 		return -1;
>> 	else
>> 		return 0;
>> ~~~
>>=20
>> As per RFC791:
>>=20
>>  Identification:  16 bits
>>=20
>>    An identifying value assigned by the sender to aid in assembling =
the
>>    fragments of a datagram.
>=20
> The IP header id is meaningless in most TCP sessions.
> Good TCP implementations use PMTU discovery which sets the Don't =
Fragment bit.
> With DF, the IP id is unused (since no fragmentation).
> Many implementations just send 0 since generating unique IP id =
requires an
> atomic operation which is potential bottleneck.

So, is my question correct and the code is wrong?