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tcp: reorganize tcp_sock_write_txrx group for variables later

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Use the first 3-byte hole at the beginning of the tcp_sock_write_txrx
group for 'noneagle'/'rate_app_limited' to fill in the existing hole
in later patches. Therefore, the group size of tcp_sock_write_txrx is
reduced from 92 + 4 to 91 + 4. In addition, the group size of
tcp_sock_write_rx is changed to 96 to fit in the pahole outcome.
Below are the trimmed pahole outcomes before and after this patch:

[BEFORE THIS PATCH]
struct tcp_sock {
    [...]
    __cacheline_group_begin__tcp_sock_write_txrx[0]; /*  2521     0 */
    /* XXX 3 bytes hole, try to pack */

    [...]
    struct tcp_options_received rx_opt;              /*  2588    24 */
    u8                         nonagle:4;            /*  2612: 0  1 */
    u8                         rate_app_limited:1;   /*  2612: 4  1 */
    /* XXX 3 bits hole, try to pack */

    __cacheline_group_end__tcp_sock_write_txrx[0];   /*  2613     0 */
    /* XXX 3 bytes hole, try to pack */

    __cacheline_group_begin__tcp_sock_write_rx[0] __attribute__((__aligned__(8))); /*  2616     0 */

    [...]
    __cacheline_group_end__tcp_sock_write_rx[0];     /*  2712     0 */

    [...]
    /* size: 3200, cachelines: 50, members: 161 */
}

[AFTER THIS PATCH]
struct tcp_sock {
    [...]
    __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 */
    /* XXX 2 bytes hole, try to pack */

    [...]
    struct tcp_options_received rx_opt;              /*  2588    24 */

    __cacheline_group_end__tcp_sock_write_txrx[0];   /*  2612     0 */
    /* XXX 4 bytes hole, try to pack */

    __cacheline_group_begin__tcp_sock_write_rx[0] __attribute__((__aligned__(8))); /*  2616     0 */

    [...]
    __cacheline_group_end__tcp_sock_write_rx[0];     /*  2712     0 */

    [...]
    /* size: 3200, cachelines: 50, members: 161 */
}

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250911110642.87529-4-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Chia-Yu Chang 2025-09-11 13:06:31 +02:00 committed by Jakub Kicinski
parent 61b2f7baa9
commit c3426ba2ed
2 changed files with 4 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/tcp.h
View File

@ -285,6 +285,8 @@ struct tcp_sock {
* Header prediction flags
* 0x5?10 << 16 + snd_wnd in net byte order
*/
u8 nonagle : 4,/* Disable Nagle algorithm? */
rate_app_limited:1; /* rate_{delivered,interval_us} limited? */
__be32 pred_flags;
u64 tcp_clock_cache; /* cache last tcp_clock_ns() (see tcp_mstamp_refresh()) */
u64 tcp_mstamp; /* most recent packet received/sent */
@ -303,8 +305,6 @@ struct tcp_sock {
* Options received (usually on last packet, some only on SYN packets).
*/
struct tcp_options_received rx_opt;
u8 nonagle : 4,/* Disable Nagle algorithm? */
rate_app_limited:1; /* rate_{delivered,interval_us} limited? */
__cacheline_group_end(tcp_sock_write_txrx);
/* RX read-write hotpath cache lines */

4
net/ipv4/tcp.c
View File

@ -5145,7 +5145,7 @@ static void __init tcp_struct_check(void)
/* 32bit arches with 8byte alignment on u64 fields might need padding
* before tcp_clock_cache.
*/
CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 92 + 4);
CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 91 + 4);
/* RX read-write hotpath cache lines */
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_rx, bytes_received);
@ -5162,7 +5162,7 @@ static void __init tcp_struct_check(void)
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_rx, bytes_acked);
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_rx, rcv_rtt_est);
CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_rx, rcvq_space);
CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_rx, 99);
CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_rx, 96);
}
void __init tcp_init(void)