check whether ip_id continuity needs to be checked when two TCP packets are merged.

GRO jiangheng (G) 3 participants 4 messages Apr 15, 2023 – Aug 26, 2024

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jiangheng (G)

author

2023-04-15 14:45 UTC #0 lore raw

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:

lib/gro/gro_tcp4.h +2 -4

index 212f97a042..06faead7b5 100644
@@ -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)
                /* append the new packet */
                return 1;
-       else if ((sent_seq + tcp_dl == item->sent_seq) && (is_atomic ||
-                               (ip_id + item->nb_merged == item->ip_id)))
+       else if (sent_seq + tcp_dl == item->sent_seq)
                /* pre-pend the new packet */
                return -1;

Hu, Jiayu

2023-04-20 02:30 UTC #1 lore raw

Hi Cheng,

Quoted 21 lines

-----Original Message-----
From: jiangheng (G) <[email protected]>
Sent: Saturday, April 15, 2023 10:46 PM
To: [email protected]; Hu, Jiayu <[email protected]>; [email protected]
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:
lib/gro/gro_tcp4.h index renamed from lib/gro/gro_tcp4.h +0 -0
212f97a042..06faead7b5 100644

lib/gro/gro_tcp4.h check_seq_option(struct gro_tcp4_item *item, · line 294

Quoted 6 lines

lib/gro/gro_tcp4.h +1 -2

@@ -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

Quoted 7 lines

lib/gro/gro_tcp4.h +1 -2

                /* append the new packet */
                return 1;
-       else if ((sent_seq + tcp_dl == item->sent_seq) && (is_atomic ||
-                               (ip_id + item->nb_merged == item->ip_id)))
+       else if (sent_seq + tcp_dl == item->sent_seq)
                /* pre-pend the new packet */
                return -1;

Stephen Hemminger

2023-04-20 02:46 UTC #2 lore raw

Quoted 33 lines · Jiayu

Hi Cheng,
Quoted 21 lines
-----Original Message-----
From: jiangheng (G) <[email protected]>
Sent: Saturday, April 15, 2023 10:46 PM
To: [email protected]; Hu, Jiayu <[email protected]>; [email protected]
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:
lib/gro/gro_tcp4.h index renamed from lib/gro/gro_tcp4.h +0 -0
212f97a042..06faead7b5 100644
lib/gro/gro_tcp4.h check_seq_option(struct gro_tcp4_item *item, · line 294
Quoted 6 lines
lib/gro/gro_tcp4.h +1 -2
@@ -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().

Quoted 1 line

Is this change specific to your case? Can you give more details on why it helps?

Many OS's don't change IP ID if DF bit is set.
See RFC 6864 for details

Quoted 1 line

Quoted 1 line
The IPv4 ID field MUST NOT be used for purposes other than

fragmentation and reassembly.

Stephen Hemminger

2024-08-26 15:48 UTC #3 lore raw

In reply to Hu, Jiayu

Quoted 33 lines · Jiayu

Hi Cheng,
Quoted 21 lines
-----Original Message-----
From: jiangheng (G) <[email protected]>
Sent: Saturday, April 15, 2023 10:46 PM
To: [email protected]; Hu, Jiayu <[email protected]>; [email protected]
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:
lib/gro/gro_tcp4.h index renamed from lib/gro/gro_tcp4.h +0 -0
212f97a042..06faead7b5 100644
lib/gro/gro_tcp4.h check_seq_option(struct gro_tcp4_item *item, · line 294
Quoted 6 lines
lib/gro/gro_tcp4.h +1 -2
@@ -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().

Quoted 4 lines

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.