tcp: accecn: add AccECN rx byte counters

These three byte counters track IP ECN field payload byte sums for
all arriving (acceptable) packets for ECT0, ECT1, and CE. The
AccECN option (added by a later patch in the series) echoes these
counters back to sender side; therefore, it is placed within the
group of tcp_sock_write_txrx.

Below are the pahole outcomes before and after this patch, in which
the group size of tcp_sock_write_txrx is increased from 95 + 4 to
107 + 4 and an extra 4-byte hole is created but will be exploited
in later patches:

[BEFORE THIS PATCH]
struct tcp_sock {
    [...]
    u32                        delivered_ce;         /*  2576     4 */
    u32                        received_ce;          /*  2580     4 */
    u32                        app_limited;          /*  2584     4 */
    u32                        rcv_wnd;              /*  2588     4 */
    struct tcp_options_received rx_opt;              /*  2592    24 */
    __cacheline_group_end__tcp_sock_write_txrx[0];   /*  2616     0 */

    [...]
    /* size: 3200, cachelines: 50, members: 166 */
}

[AFTER THIS PATCH]
struct tcp_sock {
    [...]
    u32                        delivered_ce;         /*  2576     4 */
    u32                        received_ce;          /*  2580     4 */
    u32                        received_ecn_bytes[3];/*  2584    12 */
    u32                        app_limited;          /*  2596     4 */
    u32                        rcv_wnd;              /*  2600     4 */
    struct tcp_options_received rx_opt;              /*  2604    24 */
    __cacheline_group_end__tcp_sock_write_txrx[0];   /*  2628     0 */
    /* XXX 4 bytes hole, try to pack */

    [...]
    /* size: 3200, cachelines: 50, members: 167 */
}

Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Co-developed-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
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/20250916082434.100722-4-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 28 insertions, 1 deletions

diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h
index da0b355418bd..1a41a459aa07 100644
--- a/include/net/tcp_ecn.h
+++ b/include/net/tcp_ecn.h
@@ -171,7 +171,7 @@ static inline void tcp_accecn_third_ack(struct sock *sk,
 
 /* Updates Accurate ECN received counters from the received IP ECN field */
 static inline void tcp_ecn_received_counters(struct sock *sk,
-					     const struct sk_buff *skb)
+					     const struct sk_buff *skb, u32 len)
 {
 	u8 ecnfield = TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK;
 	u8 is_ce = INET_ECN_is_ce(ecnfield);
@@ -191,9 +191,24 @@ static inline void tcp_ecn_received_counters(struct sock *sk,
 		tp->received_ce += pcount;
 		tp->received_ce_pending = min(tp->received_ce_pending + pcount,
 					      0xfU);
+
+		if (len > 0)
+			tp->received_ecn_bytes[ecnfield - 1] += len;
 	}
 }
 
+/* AccECN specification, 2.2: [...] A Data Receiver maintains four counters
+ * initialized at the start of	the half-connection. [...] These byte counters
+ * reflect only the TCP payload length, excluding TCP header and TCP options.
+ */
+static inline void tcp_ecn_received_counters_payload(struct sock *sk,
+						     const struct sk_buff *skb)
+{
+	const struct tcphdr *th = (const struct tcphdr *)skb->data;
+
+	tcp_ecn_received_counters(sk, skb, skb->len - th->doff * 4);
+}
+
 /* AccECN specification, 5.1: [...] a server can determine that it
  * negotiated AccECN as [...] if the ACK contains an ACE field with
  * the value 0b010 to 0b111 (decimal 2 to 7).
@@ -232,10 +247,22 @@ static inline bool tcp_accecn_syn_requested(const struct tcphdr *th)
 	return ace && ace != 0x3;
 }
 
+static inline void __tcp_accecn_init_bytes_counters(int *counter_array)
+{
+	BUILD_BUG_ON(INET_ECN_ECT_1 != 0x1);
+	BUILD_BUG_ON(INET_ECN_ECT_0 != 0x2);
+	BUILD_BUG_ON(INET_ECN_CE != 0x3);
+
+	counter_array[INET_ECN_ECT_1 - 1] = 0;
+	counter_array[INET_ECN_ECT_0 - 1] = 0;
+	counter_array[INET_ECN_CE - 1] = 0;
+}
+
 static inline void tcp_accecn_init_counters(struct tcp_sock *tp)
 {
 	tp->received_ce = 0;
 	tp->received_ce_pending = 0;
+	__tcp_accecn_init_bytes_counters(tp->received_ecn_bytes);
 }
 
 /* Used for make_synack to form the ACE flags */