linux-stable.git/include/linux/tcp.h, branch v7.0.10

tcp: move tp->chrono_type next tp->chrono_stat[]

2026-05-23T11:09:18+00:00

[ Upstream commit 4b78c9cbd8f1fbb9517aee48b372646f4cf05442 ]

chrono_type is currently in tcp_sock_read_txrx group, which
is supposed to hold read-mostly fields.

But chrono_type is mostly written in tx path, it should
be moved to tcp_sock_write_tx group, close to other
chrono fields (chrono_stat[], chrono_start).

Note this adds holes, but data locality is far more important.

Use a full u8 for the time being, compiler can generate
more efficient code.

Signed-off-by: Eric Dumazet 
Reviewed-by: Neal Cardwell 
Link: https://patch.msgid.link/20260308122302.2895067-1-edumazet@google.com
Signed-off-by: Jakub Kicinski 
Stable-dep-of: 267bf3cf9a6f ("tcp: annotate data-races in tcp_get_info_chrono_stats()")
Signed-off-by: Sasha Levin

tcp: accecn: detect loss ACK w/ AccECN option and add TCP_ACCECN_OPTION_PERSIST

2026-02-03T14:13:25+00:00

Detect spurious retransmission of a previously sent ACK carrying the
AccECN option after the second retransmission. Since this might be caused
by the middlebox dropping ACK with options it does not recognize, disable
the sending of the AccECN option in all subsequent ACKs. This patch
follows Section 3.2.3.2.2 of AccECN spec (RFC9768), and a new field
(accecn_opt_sent_w_dsack) is added to indicate that an AccECN option was
sent with duplicate SACK info.

Also, a new AccECN option sending mode is added to tcp_ecn_option sysctl:
(TCP_ECN_OPTION_PERSIST), which ignores the AccECN fallback policy and
persistently sends AccECN option once it fits into TCP option space.

Signed-off-by: Chia-Yu Chang 
Acked-by: Paolo Abeni 
Reviewed-by: Eric Dumazet 
Link: https://patch.msgid.link/20260131222515.8485-13-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni

tcp: try to avoid safer when ACKs are thinned

2026-02-03T14:13:24+00:00

Add newly acked pkts EWMA. When ACK thinning occurs, select
between safer and unsafe cep delta in AccECN processing based
on it. If the packets ACKed per ACK tends to be large, don't
conservatively assume ACE field overflow.

This patch uses the existing 2-byte holes in the rx group for new
u16 variables withtout creating more holes. Below are the pahole
outcomes before and after this patch:

[BEFORE THIS PATCH]
struct tcp_sock {
    [...]
    u32                        delivered_ecn_bytes[3]; /*  2744    12 */
    /* XXX 4 bytes hole, try to pack */

    [...]
    __cacheline_group_end__tcp_sock_write_rx[0];       /*  2816     0 */

    [...]
    /* size: 3264, cachelines: 51, members: 177 */
}

[AFTER THIS PATCH]
struct tcp_sock {
    [...]
    u32                        delivered_ecn_bytes[3]; /*  2744    12 */
    u16                        pkts_acked_ewma;        /*  2756     2 */
    /* XXX 2 bytes hole, try to pack */

    [...]
    __cacheline_group_end__tcp_sock_write_rx[0];       /*  2816     0 */

    [...]
    /* size: 3264, cachelines: 51, members: 178 */
}

Signed-off-by: Ilpo Järvinen 
Co-developed-by: Chia-Yu Chang 
Signed-off-by: Chia-Yu Chang 
Acked-by: Paolo Abeni 
Reviewed-by: Eric Dumazet 
Link: https://patch.msgid.link/20260131222515.8485-2-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni

tcp: preserve const qualifier in tcp_rsk() and inet_rsk()

2026-01-22T03:20:04+00:00

We can change tcp_rsk() and inet_rsk() to propagate their argument
const qualifier thanks to container_of_const().

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20260120125353.1470456-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: move mtu_info to remove two 32bit holes

2025-09-23T00:55:25+00:00

This removes 8bytes waste on 64bit builds.

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250919204856.2977245-8-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: move tcp_clean_acked to tcp_sock_read_tx group

2025-09-23T00:55:25+00:00

tp->tcp_clean_acked is fetched in tx path when snd_una is updated.

This field thus belongs to tcp_sock_read_tx group.

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250919204856.2977245-7-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: move recvmsg_inq to tcp_sock_read_txrx

2025-09-23T00:55:25+00:00

Fill a hole in tcp_sock_read_txrx, instead of possibly wasting
a cache line.

Note that tcp_recvmsg_locked() is also reading tp->repair,
so this removes one cache line miss in tcp recvmsg().

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250919204856.2977245-6-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: move tcp->rcv_tstamp to tcp_sock_write_txrx group

2025-09-23T00:55:24+00:00

tcp_ack() writes this field, it belongs to tcp_sock_write_txrx.

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250919204856.2977245-5-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: accecn: AccECN option failure handling

2025-09-18T06:47:52+00:00

AccECN option may fail in various way, handle these:
- Attempt to negotiate the use of AccECN on the 1st retransmitted SYN
	- From the 2nd retransmitted SYN, stop AccECN negotiation
- Remove option from SYN/ACK rexmits to handle blackholes
- If no option arrives in SYN/ACK, assume Option is not usable
        - If an option arrives later, re-enabled
- If option is zeroed, disable AccECN option processing

This patch use existing padding bits in tcp_request_sock and
holes in tcp_sock without increasing the size.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: Chia-Yu Chang 
Reviewed-by: Eric Dumazet 
Link: https://patch.msgid.link/20250916082434.100722-9-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni

tcp: accecn: AccECN option send control

2025-09-18T06:47:52+00:00

Instead of sending the option in every ACK, limit sending to
those ACKs where the option is necessary:
- Handshake
- "Change-triggered ACK" + the ACK following it. The
  2nd ACK is necessary to unambiguously indicate which
  of the ECN byte counters in increasing. The first
  ACK has two counters increasing due to the ecnfield
  edge.
- ACKs with CE to allow CEP delta validations to take
  advantage of the option.
- Force option to be sent every at least once per 2^22
  bytes. The check is done using the bit edges of the
  byte counters (avoids need for extra variables).
- AccECN option beacon to send a few times per RTT even if
  nothing in the ECN state requires that. The default is 3
  times per RTT, and its period can be set via
  sysctl_tcp_ecn_option_beacon.

Below are the pahole outcomes before and after this patch,
in which the group size of tcp_sock_write_tx is increased
from 89 to 97 due to the new u64 accecn_opt_tstamp member:

[BEFORE THIS PATCH]
struct tcp_sock {
    [...]
    u64                        tcp_wstamp_ns;        /*  2488     8 */
    struct list_head           tsorted_sent_queue;   /*  2496    16 */

    [...]
    __cacheline_group_end__tcp_sock_write_tx[0];     /*  2521     0 */
    __cacheline_group_begin__tcp_sock_write_txrx[0]; /*  2521     0 */
    u8                         nonagle:4;            /*  2521: 0  1 */
    u8                         rate_app_limited:1;   /*  2521: 4  1 */
    /* XXX 3 bits hole, try to pack */

    /* Force alignment to the next boundary: */
    u8                         :0;
    u8                         received_ce_pending:4;/*  2522: 0  1 */
    u8                         unused2:4;            /*  2522: 4  1 */
    u8                         accecn_minlen:2;      /*  2523: 0  1 */
    u8                         est_ecnfield:2;       /*  2523: 2  1 */
    u8                         unused3:4;            /*  2523: 4  1 */

    [...]
    __cacheline_group_end__tcp_sock_write_txrx[0];   /*  2628     0 */

    [...]
    /* size: 3200, cachelines: 50, members: 171 */
}

[AFTER THIS PATCH]
struct tcp_sock {
    [...]
    u64                        tcp_wstamp_ns;        /*  2488     8 */
    u64                        accecn_opt_tstamp;    /*  2596     8 */
    struct list_head           tsorted_sent_queue;   /*  2504    16 */

    [...]
    __cacheline_group_end__tcp_sock_write_tx[0];     /*  2529     0 */
    __cacheline_group_begin__tcp_sock_write_txrx[0]; /*  2529     0 */
    u8                         nonagle:4;            /*  2529: 0  1 */
    u8                         rate_app_limited:1;   /*  2529: 4  1 */
    /* XXX 3 bits hole, try to pack */

    /* Force alignment to the next boundary: */
    u8                         :0;
    u8                         received_ce_pending:4;/*  2530: 0  1 */
    u8                         unused2:4;            /*  2530: 4  1 */
    u8                         accecn_minlen:2;      /*  2531: 0  1 */
    u8                         est_ecnfield:2;       /*  2531: 2  1 */
    u8                         accecn_opt_demand:2;  /*  2531: 4  1 */
    u8                         prev_ecnfield:2;      /*  2531: 6  1 */

    [...]
    __cacheline_group_end__tcp_sock_write_txrx[0];   /*  2636     0 */

    [...]
    /* size: 3200, cachelines: 50, members: 173 */
}

Signed-off-by: Chia-Yu Chang 
Co-developed-by: Ilpo Järvinen 
Signed-off-by: Ilpo Järvinen 
Reviewed-by: Eric Dumazet 
Link: https://patch.msgid.link/20250916082434.100722-8-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni