net: SO_INCOMING_CPU setsockopt() support

SO_INCOMING_CPU as added in commit 2c8c56e15df3 was a getsockopt() command
to fetch incoming cpu handling a particular TCP flow after accept()

This commits adds setsockopt() support and extends SO_REUSEPORT selection
logic : If a TCP listener or UDP socket has this option set, a packet is
delivered to this socket only if CPU handling the packet matches the specified
one.

This allows to build very efficient TCP servers, using one listener per
RX queue, as the associated TCP listener should only accept flows handled
in softirq by the same cpu.
This provides optimal NUMA behavior and keep cpu caches hot.

Note that __inet_lookup_listener() still has to iterate over the list of
all listeners. Following patch puts sk_refcnt in a different cache line
to let this iteration hit only shared and read mostly cache lines.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -150,6 +150,7 @@ typedef __u64 __bitwise __addrpair;
  *	@skc_node: main hash linkage for various protocol lookup tables
  *	@skc_nulls_node: main hash linkage for TCP/UDP/UDP-Lite protocol
  *	@skc_tx_queue_mapping: tx queue number for this connection
+ *	@skc_incoming_cpu: record/match cpu processing incoming packets
  *	@skc_refcnt: reference count
  *
  *	This is the minimal network layer representation of sockets, the header
@@ -212,6 +213,8 @@ struct sock_common {
 		struct hlist_nulls_node skc_nulls_node;
 	};
 	int			skc_tx_queue_mapping;
+	int			skc_incoming_cpu;
+
 	atomic_t		skc_refcnt;
 	/* private: */
 	int                     skc_dontcopy_end[0];
@@ -274,7 +277,6 @@ struct cg_proto;
   *	@sk_rcvtimeo: %SO_RCVTIMEO setting
   *	@sk_sndtimeo: %SO_SNDTIMEO setting
   *	@sk_rxhash: flow hash received from netif layer
-  *	@sk_incoming_cpu: record cpu processing incoming packets
   *	@sk_txhash: computed flow hash for use on transmit
   *	@sk_filter: socket filtering instructions
   *	@sk_timer: sock cleanup timer
@@ -331,6 +333,7 @@ struct sock {
 #define sk_v6_daddr		__sk_common.skc_v6_daddr
 #define sk_v6_rcv_saddr	__sk_common.skc_v6_rcv_saddr
 #define sk_cookie		__sk_common.skc_cookie
+#define sk_incoming_cpu		__sk_common.skc_incoming_cpu
 
 	socket_lock_t		sk_lock;
 	struct sk_buff_head	sk_receive_queue;
@@ -353,11 +356,6 @@ struct sock {
 #ifdef CONFIG_RPS
 	__u32			sk_rxhash;
 #endif
-	u16			sk_incoming_cpu;
-	/* 16bit hole
-	 * Warned : sk_incoming_cpu can be set from softirq,
-	 * Do not use this hole without fully understanding possible issues.
-	 */
 
 	__u32			sk_txhash;
 #ifdef CONFIG_NET_RX_BUSY_POLL

net/core/sock.c

@@ -988,6 +988,10 @@ set_rcvbuf:
 					 sk->sk_max_pacing_rate);
 		break;
 
+	case SO_INCOMING_CPU:
+		sk->sk_incoming_cpu = val;
+		break;
+
 	default:
 		ret = -ENOPROTOOPT;
 		break;
@@ -2379,6 +2383,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 	sk->sk_max_pacing_rate = ~0U;
 	sk->sk_pacing_rate = ~0U;
+	sk->sk_incoming_cpu = -1;
 	/*
 	 * Before updating sk_refcnt, we must commit prior changes to memory
 	 * (Documentation/RCU/rculist_nulls.txt for details)

net/ipv4/inet_hashtables.c

@@ -185,6 +185,8 @@ static inline int compute_score(struct sock *sk, struct net *net,
 				return -1;
 			score += 4;
 		}
+		if (sk->sk_incoming_cpu == raw_smp_processor_id())
+			score++;
 	}
 	return score;
 }

net/ipv4/udp.c

@@ -375,7 +375,8 @@ static inline int compute_score(struct sock *sk, struct net *net,
 			return -1;
 		score += 4;
 	}
-
+	if (sk->sk_incoming_cpu == raw_smp_processor_id())
+		score++;
 	return score;
 }
 
@@ -419,6 +420,9 @@ static inline int compute_score2(struct sock *sk, struct net *net,
 		score += 4;
 	}
 
+	if (sk->sk_incoming_cpu == raw_smp_processor_id())
+		score++;
+
 	return score;
 }
 

net/ipv6/inet6_hashtables.c

@@ -114,6 +114,8 @@ static inline int compute_score(struct sock *sk, struct net *net,
 				return -1;
 			score++;
 		}
+		if (sk->sk_incoming_cpu == raw_smp_processor_id())
+			score++;
 	}
 	return score;
 }

net/ipv6/udp.c

@@ -182,10 +182,12 @@ static inline int compute_score(struct sock *sk, struct net *net,
 		score++;
 	}
 
+	if (sk->sk_incoming_cpu == raw_smp_processor_id())
+		score++;
+
 	return score;
 }
 
-#define SCORE2_MAX (1 + 1 + 1)
 static inline int compute_score2(struct sock *sk, struct net *net,
 				 const struct in6_addr *saddr, __be16 sport,
 				 const struct in6_addr *daddr,
@@ -223,6 +225,9 @@ static inline int compute_score2(struct sock *sk, struct net *net,
 		score++;
 	}
 
+	if (sk->sk_incoming_cpu == raw_smp_processor_id())
+		score++;
+
 	return score;
 }
 
@@ -251,8 +256,7 @@ begin:
 				hash = udp6_ehashfn(net, daddr, hnum,
 						    saddr, sport);
 				matches = 1;
-			} else if (score == SCORE2_MAX)
-				goto exact_match;
+			}
 		} else if (score == badness && reuseport) {
 			matches++;
 			if (reciprocal_scale(hash, matches) == 0)
@@ -269,7 +273,6 @@ begin:
 		goto begin;
 
 	if (result) {
-exact_match:
 		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
 			result = NULL;
 		else if (unlikely(compute_score2(result, net, saddr, sport,