diff mbox series

[v4,net-next,3/3] ipv4/udp: Add 4-tuple hash for connected socket

Message ID 20241012012918.70888-4-lulie@linux.alibaba.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series udp: Add 4-tuple hash for connected sockets | expand

Commit Message

Philo Lu Oct. 12, 2024, 1:29 a.m. UTC 
Currently, the udp_table has two hash table, the port hash and portaddr
hash. Usually for UDP servers, all sockets have the same local port and
addr, so they are all on the same hash slot within a reuseport group.

In some applications, UDP servers use connect() to manage clients. In
particular, when firstly receiving from an unseen 4 tuple, a new socket
is created and connect()ed to the remote addr:port, and then the fd is
used exclusively by the client.

Once there are connected sks in a reuseport group, udp has to score all
sks in the same hash2 slot to find the best match. This could be
inefficient with a large number of connections, resulting in high
softirq overhead.

To solve the problem, this patch implement 4-tuple hash for connected
udp sockets. During connect(), hash4 slot is updated, as well as a
corresponding counter, hash4_cnt, in hslot2. In __udp4_lib_lookup(),
hslot4 will be searched firstly if the counter is non-zero. Otherwise,
hslot2 is used like before. Note that only connected sockets enter this
hash4 path, while un-connected ones are not affected.

Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
Signed-off-by: Cambda Zhu <cambda@linux.alibaba.com>
Signed-off-by: Fred Chen <fred.cc@alibaba-inc.com>
Signed-off-by: Yubing Qiu <yubing.qiuyubing@alibaba-inc.com>
---
 include/net/udp.h |   3 +-
 net/ipv4/udp.c    | 142 ++++++++++++++++++++++++++++++++++++++++++++--
 net/ipv6/udp.c    |   2 +-
 3 files changed, 141 insertions(+), 6 deletions(-)

Comments

Paolo Abeni Oct. 14, 2024, 10:19 a.m. UTC | #1 
On 10/12/24 03:29, Philo Lu wrote:
> Currently, the udp_table has two hash table, the port hash and portaddr
> hash. Usually for UDP servers, all sockets have the same local port and
> addr, so they are all on the same hash slot within a reuseport group.
> 
> In some applications, UDP servers use connect() to manage clients. In
> particular, when firstly receiving from an unseen 4 tuple, a new socket
> is created and connect()ed to the remote addr:port, and then the fd is
> used exclusively by the client.

How do you handle the following somewhat racing scenario? a 2nd packet 
beloning to the same 4-tulpe lands into the unconnected socket receive 
queue just after the 1st one, before the connected socket is created. 
The server process such packet after the connected socket creation.

How many connected sockets is your system serving concurrently? Possibly 
it would make sense to allocate a larger hash table for the connected 
UDP sockets, using separate/different min/max/scale values WRT to the 
unconnected tables.

Cheers,

Paolo
Philo Lu Oct. 16, 2024, 7:28 a.m. UTC | #2 
On 2024/10/14 18:19, Paolo Abeni wrote:
> On 10/12/24 03:29, Philo Lu wrote:
>> Currently, the udp_table has two hash table, the port hash and portaddr
>> hash. Usually for UDP servers, all sockets have the same local port and
>> addr, so they are all on the same hash slot within a reuseport group.
>>
>> In some applications, UDP servers use connect() to manage clients. In
>> particular, when firstly receiving from an unseen 4 tuple, a new socket
>> is created and connect()ed to the remote addr:port, and then the fd is
>> used exclusively by the client.
> 
> How do you handle the following somewhat racing scenario? a 2nd packet 
> beloning to the same 4-tulpe lands into the unconnected socket receive 
> queue just after the 1st one, before the connected socket is created. 
> The server process such packet after the connected socket creation.
> 

One method is to address it in application. Application maintains the 
information of connections, and it knows which connection to deliver 
incoming packets.

If the 2nd packet comes from the "listen" socket (i.e., the initial 
unconnected socket), app can search for the connection of it. Note that 
upon the 1st packet receiving, the connection is already created though 
the socket is not ready, so it can be found for the 2nd packet.

In this case, maybe several packets are processed with this method until 
the new connected socket created. Then it runs as we expect.

So I think it cannot be prevented but can be handled, depending on how 
applications use it.

> How many connected sockets is your system serving concurrently? Possibly 

About 10000 conns in general. So current same-sized hash4 table is 
enough for us now.

> it would make sense to allocate a larger hash table for the connected 
> UDP sockets, using separate/different min/max/scale values WRT to the 
> unconnected tables.
> 

Agreed that it's a good idea. But imo it could be left as future work 
when we definitely need it.

Thanks.
diff mbox series

Patch

diff --git a/include/net/udp.h b/include/net/udp.h
index 80f9622d0db3..5633b51cf8d4 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -226,7 +226,7 @@  static inline int udp_lib_hash(struct sock *sk)
 }
 
 void udp_lib_unhash(struct sock *sk);
-void udp_lib_rehash(struct sock *sk, u16 new_hash);
+void udp_lib_rehash(struct sock *sk, u16 new_hash, u16 new_hash4);
 
 static inline void udp_lib_close(struct sock *sk, long timeout)
 {
@@ -319,6 +319,7 @@  int udp_rcv(struct sk_buff *skb);
 int udp_ioctl(struct sock *sk, int cmd, int *karg);
 int udp_init_sock(struct sock *sk);
 int udp_pre_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
+int udp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
 int __udp_disconnect(struct sock *sk, int flags);
 int udp_disconnect(struct sock *sk, int flags);
 __poll_t udp_poll(struct file *file, struct socket *sock, poll_table *wait);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 1498ccb79c58..d7e3866617e0 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -478,6 +478,27 @@  static struct sock *udp4_lib_lookup2(const struct net *net,
 	return result;
 }
 
+static struct sock *udp4_lib_lookup4(const struct net *net,
+				     __be32 saddr, __be16 sport,
+				     __be32 daddr, unsigned int hnum,
+				     int dif, int sdif,
+				     struct udp_table *udptable)
+{
+	unsigned int hash4 = udp_ehashfn(net, daddr, hnum, saddr, sport);
+	const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
+	struct udp_hslot *hslot4 = udp_hashslot4(udptable, hash4);
+	struct udp_sock *up;
+	struct sock *sk;
+
+	INET_ADDR_COOKIE(acookie, saddr, daddr);
+	udp_lrpa_for_each_entry_rcu(up, &hslot4->head) {
+		sk = (struct sock *)up;
+		if (inet_match(net, sk, acookie, ports, dif, sdif))
+			return sk;
+	}
+	return NULL;
+}
+
 /* UDP is nearly always wildcards out the wazoo, it makes no sense to try
  * harder than this. -DaveM
  */
@@ -493,6 +514,12 @@  struct sock *__udp4_lib_lookup(const struct net *net, __be32 saddr,
 	hash2 = ipv4_portaddr_hash(net, daddr, hnum);
 	hslot2 = udp_hashslot2(udptable, hash2);
 
+	if (UDP_HSLOT_MAIN(hslot2)->hash4_cnt) {
+		result = udp4_lib_lookup4(net, saddr, sport, daddr, hnum, dif, sdif, udptable);
+		if (result) /* udp4_lib_lookup4 return sk or NULL */
+			return result;
+	}
+
 	/* Lookup connected or non-wildcard socket */
 	result = udp4_lib_lookup2(net, saddr, sport,
 				  daddr, hnum, dif, sdif,
@@ -1931,6 +1958,85 @@  int udp_pre_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 }
 EXPORT_SYMBOL(udp_pre_connect);
 
+/* In hash4, rehash can also happen in connect(), where hash4_cnt keeps unchanged. */
+static void udp4_rehash4(struct udp_table *udptable, struct sock *sk, u16 newhash4)
+{
+	struct udp_hslot *hslot4, *nhslot4;
+
+	hslot4 = udp_hashslot4(udptable, udp_sk(sk)->udp_lrpa_hash);
+	nhslot4 = udp_hashslot4(udptable, newhash4);
+	udp_sk(sk)->udp_lrpa_hash = newhash4;
+
+	if (hslot4 != nhslot4) {
+		spin_lock_bh(&hslot4->lock);
+		hlist_del_init_rcu(&udp_sk(sk)->udp_lrpa_node);
+		hslot4->count--;
+		spin_unlock_bh(&hslot4->lock);
+
+		synchronize_rcu();
+
+		spin_lock_bh(&nhslot4->lock);
+		hlist_add_head_rcu(&udp_sk(sk)->udp_lrpa_node, &nhslot4->head);
+		nhslot4->count++;
+		spin_unlock_bh(&nhslot4->lock);
+	}
+}
+
+/* call with sock lock */
+static void udp4_hash4(struct sock *sk)
+{
+	struct udp_hslot *hslot, *hslot4;
+	struct udp_hslot_main *hslotm2;
+	struct net *net = sock_net(sk);
+	struct udp_table *udptable;
+	unsigned int hash;
+
+	if (sk_unhashed(sk) || inet_sk(sk)->inet_rcv_saddr == htonl(INADDR_ANY))
+		return;
+
+	hash = udp_ehashfn(net, inet_sk(sk)->inet_rcv_saddr, inet_sk(sk)->inet_num,
+			   inet_sk(sk)->inet_daddr, inet_sk(sk)->inet_dport);
+
+	udptable = net->ipv4.udp_table;
+	if (udp_hashed4(sk)) {
+		udp4_rehash4(udptable, sk, hash);
+		return;
+	}
+
+	hslot = udp_hashslot(udptable, net, udp_sk(sk)->udp_port_hash);
+	hslotm2 = udp_hashslot2_main(udptable, udp_sk(sk)->udp_portaddr_hash);
+	hslot4 = udp_hashslot4(udptable, hash);
+	udp_sk(sk)->udp_lrpa_hash = hash;
+
+	spin_lock_bh(&hslot->lock);
+	if (rcu_access_pointer(sk->sk_reuseport_cb))
+		reuseport_detach_sock(sk);
+
+	spin_lock(&hslot4->lock);
+	hlist_add_head_rcu(&udp_sk(sk)->udp_lrpa_node, &hslot4->head);
+	hslot4->count++;
+	spin_unlock(&hslot4->lock);
+
+	spin_lock(&hslotm2->hslot.lock);
+	hslotm2->hash4_cnt++;
+	spin_unlock(&hslotm2->hslot.lock);
+
+	spin_unlock_bh(&hslot->lock);
+}
+
+int udp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+{
+	int res;
+
+	lock_sock(sk);
+	res = __ip4_datagram_connect(sk, uaddr, addr_len);
+	if (!res)
+		udp4_hash4(sk);
+	release_sock(sk);
+	return res;
+}
+EXPORT_SYMBOL(udp_connect);
+
 int __udp_disconnect(struct sock *sk, int flags)
 {
 	struct inet_sock *inet = inet_sk(sk);
@@ -1972,7 +2078,7 @@  void udp_lib_unhash(struct sock *sk)
 {
 	if (sk_hashed(sk)) {
 		struct udp_table *udptable = udp_get_table_prot(sk);
-		struct udp_hslot *hslot, *hslot2;
+		struct udp_hslot *hslot, *hslot2, *hslot4;
 
 		hslot  = udp_hashslot(udptable, sock_net(sk),
 				      udp_sk(sk)->udp_port_hash);
@@ -1990,6 +2096,18 @@  void udp_lib_unhash(struct sock *sk)
 			hlist_del_init_rcu(&udp_sk(sk)->udp_portaddr_node);
 			hslot2->count--;
 			spin_unlock(&hslot2->lock);
+
+			if (udp_hashed4(sk)) {
+				hslot4 = udp_hashslot4(udptable, udp_sk(sk)->udp_lrpa_hash);
+				spin_lock(&hslot4->lock);
+				hlist_del_init_rcu(&udp_sk(sk)->udp_lrpa_node);
+				hslot4->count--;
+				spin_unlock(&hslot4->lock);
+
+				spin_lock(&hslot2->lock);
+				UDP_HSLOT_MAIN(hslot2)->hash4_cnt--;
+				spin_unlock(&hslot2->lock);
+			}
 		}
 		spin_unlock_bh(&hslot->lock);
 	}
@@ -1999,7 +2117,7 @@  EXPORT_SYMBOL(udp_lib_unhash);
 /*
  * inet_rcv_saddr was changed, we must rehash secondary hash
  */
-void udp_lib_rehash(struct sock *sk, u16 newhash)
+void udp_lib_rehash(struct sock *sk, u16 newhash, u16 newhash4)
 {
 	if (sk_hashed(sk)) {
 		struct udp_table *udptable = udp_get_table_prot(sk);
@@ -2031,6 +2149,19 @@  void udp_lib_rehash(struct sock *sk, u16 newhash)
 				spin_unlock(&nhslot2->lock);
 			}
 
+			if (udp_hashed4(sk)) {
+				udp4_rehash4(udptable, sk, newhash4);
+
+				if (hslot2 != nhslot2) {
+					spin_lock(&hslot2->lock);
+					UDP_HSLOT_MAIN(hslot2)->hash4_cnt--;
+					spin_unlock(&hslot2->lock);
+
+					spin_lock(&nhslot2->lock);
+					UDP_HSLOT_MAIN(nhslot2)->hash4_cnt++;
+					spin_unlock(&nhslot2->lock);
+				}
+			}
 			spin_unlock_bh(&hslot->lock);
 		}
 	}
@@ -2042,7 +2173,10 @@  void udp_v4_rehash(struct sock *sk)
 	u16 new_hash = ipv4_portaddr_hash(sock_net(sk),
 					  inet_sk(sk)->inet_rcv_saddr,
 					  inet_sk(sk)->inet_num);
-	udp_lib_rehash(sk, new_hash);
+	u16 new_hash4 = udp_ehashfn(sock_net(sk),
+				    inet_sk(sk)->inet_rcv_saddr, inet_sk(sk)->inet_num,
+				    inet_sk(sk)->inet_daddr, inet_sk(sk)->inet_dport);
+	udp_lib_rehash(sk, new_hash, new_hash4);
 }
 
 static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
@@ -2935,7 +3069,7 @@  struct proto udp_prot = {
 	.owner			= THIS_MODULE,
 	.close			= udp_lib_close,
 	.pre_connect		= udp_pre_connect,
-	.connect		= ip4_datagram_connect,
+	.connect		= udp_connect,
 	.disconnect		= udp_disconnect,
 	.ioctl			= udp_ioctl,
 	.init			= udp_init_sock,
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index bbf3352213c4..4d3dfcb48a39 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -111,7 +111,7 @@  void udp_v6_rehash(struct sock *sk)
 					  &sk->sk_v6_rcv_saddr,
 					  inet_sk(sk)->inet_num);
 
-	udp_lib_rehash(sk, new_hash);
+	udp_lib_rehash(sk, new_hash, 0); /* 4-tuple hash not implemented */
 }
 
 static int compute_score(struct sock *sk, const struct net *net,