diff mbox series

[v7,net-next,14/15] tcp: accecn: try to fit AccECN option with SACK

Message ID 20250514135642.11203-15-chia-yu.chang@nokia-bell-labs.com
State New
Headers show
Series [v7,net-next,01/15] tcp: reorganize SYN ECN code | expand

Commit Message

Chia-Yu Chang (Nokia) May 14, 2025, 1:56 p.m. UTC 
From: Ilpo Järvinen <ij@kernel.org>

As SACK blocks tend to eat all option space when there are
many holes, it is useful to compromise on sending many SACK
blocks in every ACK and try to fit AccECN option there
by reduction the number of SACK blocks. But never go below
two SACK blocks because of AccECN option.

As AccECN option is often not put to every ACK, the space
hijack is usually only temporary.

Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
---
 net/ipv4/tcp_output.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b630923c4cef..d9d3cc8dbb5b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -982,8 +982,21 @@  static int tcp_options_fit_accecn(struct tcp_out_options *opts, int required,
 		opts->num_accecn_fields--;
 		size -= TCPOLEN_ACCECN_PERFIELD;
 	}
-	if (opts->num_accecn_fields < required)
+	if (opts->num_accecn_fields < required) {
+		if (opts->num_sack_blocks > 2) {
+			/* Try to fit the option by removing one SACK block */
+			opts->num_sack_blocks--;
+			size = tcp_options_fit_accecn(opts, required,
+						      remaining +
+						      TCPOLEN_SACK_PERBLOCK,
+						      max_combine_saving);
+			if (opts->options & OPTION_ACCECN)
+				return size - TCPOLEN_SACK_PERBLOCK;
+
+			opts->num_sack_blocks++;
+		}
 		return 0;
+	}
 
 	opts->options |= OPTION_ACCECN;
 	return size;