From: Ilya Matveychikov <matvejchikov@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org, jiayu.hu@intel.com
Subject: Re: [dpdk-dev] A question about GRO neighbor packet matching
Date: Wed, 6 Dec 2017 22:38:12 +0400 [thread overview]
Message-ID: <2111ED2C-DB90-4AE3-893E-2406EFE129AD@gmail.com> (raw)
In-Reply-To: <20171206101200.031afa39@shemminger-XPS-13-9360>
> On Dec 6, 2017, at 10:12 PM, Stephen Hemminger <stephen@networkplumber.org> wrote:
>
> On Wed, 6 Dec 2017 18:02:21 +0400
> Ilya Matveychikov <matvejchikov@gmail.com> wrote:
>
>> Hello all,
>>
>>
>> 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 = iph-prev.id + 1)?
>
>
> No.
>
>> ~~~
>> lib/librte_gro/gro_tcp4.c:check_seq_option()
>> ...
>> /* check if the two packets are neighbors */
>> tcp_dl0 = pkt0->pkt_len - pkt0->l2_len - pkt0->l3_len - tcp_hl0;
>> if ((sent_seq == (item->sent_seq + tcp_dl0)) &&
>> (ip_id == (item->ip_id + 1)))
>> /* append the new packet */
>> return 1;
>> else if (((sent_seq + tcp_dl) == item->sent_seq) &&
>> ((ip_id + item->nb_merged) == item->ip_id))
>> /* pre-pend the new packet */
>> return -1;
>> else
>> return 0;
>> ~~~
>>
>> As per RFC791:
>>
>> Identification: 16 bits
>>
>> An identifying value assigned by the sender to aid in assembling the
>> fragments of a datagram.
>
> 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?
next prev parent reply other threads:[~2017-12-06 18:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-06 14:02 Ilya Matveychikov
2017-12-06 18:12 ` Stephen Hemminger
2017-12-06 18:38 ` Ilya Matveychikov [this message]
2017-12-06 23:15 ` Stephen Hemminger
2017-12-07 0:19 ` Ananyev, Konstantin
2017-12-07 1:01 ` Stephen Hemminger
2017-12-07 7:04 ` Ilya Matveychikov
2017-12-07 8:31 ` Hu, Jiayu
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