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

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

[Eric Dumazet]

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 <edumazet@google.com>
---
 include/linux/tcp.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index f72eef31fa23cc584f2f0cefacdc35cae43aa52d..c44cf9ae8d16f5cc7808a6ca78c1dad03354dccf 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -228,8 +228,7 @@ struct tcp_sock {
 	u32	sacked_out;	/* SACK'd packets			*/
 	u16	tcp_header_len;	/* Bytes of tcp header to send		*/
 	u8	scaling_ratio;	/* see tcp_win_from_space() */
-	u8	chrono_type : 2,	/* current chronograph type */
-		repair      : 1,
+	u8	repair      : 1,
 		tcp_usec_ts : 1, /* TSval values in usec */
 		is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
 		is_cwnd_limited:1,/* forward progress limited by snd_cwnd? */
@@ -264,6 +263,7 @@ struct tcp_sock {
 				 * total number of data bytes sent.
 				 */
 	u32	snd_sml;	/* Last byte of the most recently transmitted small packet */
+	u8	chrono_type;	/* current chronograph type */
 	u32	chrono_start;	/* Start time in jiffies of a TCP chrono */
 	u32	chrono_stat[3];	/* Time in jiffies for chrono_stat stats */
 	u32	write_seq;	/* Tail(+1) of data held in tcp send buffer */
-- 
2.53.0.473.g4a7958ca14-goog

Re: [PATCH net-next] tcp: move tp->chrono_type next tp->chrono_stat[]

[Neal Cardwell]

n Sun, Mar 8, 2026 at 8:23 AM Eric Dumazet <edumazet@google.com> wrote:
>
> 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 <edumazet@google.com>

Reviewed-by: Neal Cardwell <ncardwell@google.com>

Thanks, Eric!

neal

Re: [PATCH net-next] tcp: move tp->chrono_type next tp->chrono_stat[]

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Sun,  8 Mar 2026 12:23:02 +0000 you wrote:
> 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).
> 
> [...]

Here is the summary with links:
  - [net-next] tcp: move tp->chrono_type next tp->chrono_stat[]
    https://git.kernel.org/netdev/net-next/c/4b78c9cbd8f1

You are awesome, thank you!
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