netdev - [PATCH net-next] tcp: reorder tcp_congestion

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Date:   Fri,  2 Apr 2021 11:10:37 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next] tcp: reorder tcp_congestion_ops for better cache locality

From: Eric Dumazet <edumazet@...gle.com>

Group all the often used fields in the first cache line,
to reduce cache line misses.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/tcp.h | 42 +++++++++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 075de26f449d27093ec6eeb114d7f53c328b2136..b34b2daf98d90930a7456f147d04e5b936185cbc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1035,44 +1035,56 @@ struct rate_sample {
 };
 
 struct tcp_congestion_ops {
-	struct list_head	list;
-	u32 key;
-	u32 flags;
-
-	/* initialize private data (optional) */
-	void (*init)(struct sock *sk);
-	/* cleanup private data  (optional) */
-	void (*release)(struct sock *sk);
+/* fast path fields are put first to fill one cache line */
 
 	/* return slow start threshold (required) */
 	u32 (*ssthresh)(struct sock *sk);
+
 	/* do new cwnd calculation (required) */
 	void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
+
 	/* call before changing ca_state (optional) */
 	void (*set_state)(struct sock *sk, u8 new_state);
+
 	/* call when cwnd event occurs (optional) */
 	void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
+
 	/* call when ack arrives (optional) */
 	void (*in_ack_event)(struct sock *sk, u32 flags);
-	/* new value of cwnd after loss (required) */
-	u32  (*undo_cwnd)(struct sock *sk);
+
 	/* hook for packet ack accounting (optional) */
 	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
+
 	/* override sysctl_tcp_min_tso_segs */
 	u32 (*min_tso_segs)(struct sock *sk);
-	/* returns the multiplier used in tcp_sndbuf_expand (optional) */
-	u32 (*sndbuf_expand)(struct sock *sk);
+
 	/* call when packets are delivered to update cwnd and pacing rate,
 	 * after all the ca_state processing. (optional)
 	 */
 	void (*cong_control)(struct sock *sk, const struct rate_sample *rs);
+
+
+	/* new value of cwnd after loss (required) */
+	u32  (*undo_cwnd)(struct sock *sk);
+	/* returns the multiplier used in tcp_sndbuf_expand (optional) */
+	u32 (*sndbuf_expand)(struct sock *sk);
+
+/* control/slow paths put last */
 	/* get info for inet_diag (optional) */
 	size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
 			   union tcp_cc_info *info);
 
-	char 		name[TCP_CA_NAME_MAX];
-	struct module 	*owner;
-};
+	char 			name[TCP_CA_NAME_MAX];
+	struct module		*owner;
+	struct list_head	list;
+	u32			key;
+	u32			flags;
+
+	/* initialize private data (optional) */
+	void (*init)(struct sock *sk);
+	/* cleanup private data  (optional) */
+	void (*release)(struct sock *sk);
+} ____cacheline_aligned_in_smp;
 
 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
-- 
2.31.0.208.g409f899ff0-goog