Merge branch 'tcp-add-fast-path-in-timer-handlers'

Eric Dumazet says:

====================
tcp: add fast path in timer handlers

As mentioned in Netconf 2024:

TCP retransmit and delack timers are not stopped from
inet_csk_clear_xmit_timer() because we do not define
INET_CSK_CLEAR_TIMERS.

Enabling INET_CSK_CLEAR_TIMERS leads to lower performance,
mainly because del_timer() and mod_timer() happen from
different cpus quite often.

What we can do instead is to add fast paths to tcp_write_timer()
and tcp_delack_timer() to avoid socket spinlock acquisition.
====================

Link: https://patch.msgid.link/20241002173042.917928-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

8 files changed, 49 insertions, 24 deletions

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index c0deaafebfdc..3c82fad904d4 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -197,12 +197,12 @@ static inline void inet_csk_clear_xmit_timer(struct sock *sk, const int what)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
 	if (what == ICSK_TIME_RETRANS || what == ICSK_TIME_PROBE0) {
-		icsk->icsk_pending = 0;
+		smp_store_release(&icsk->icsk_pending, 0);
 #ifdef INET_CSK_CLEAR_TIMERS
 		sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
 #endif
 	} else if (what == ICSK_TIME_DACK) {
-		icsk->icsk_ack.pending = 0;
+		smp_store_release(&icsk->icsk_ack.pending, 0);
 		icsk->icsk_ack.retry = 0;
 #ifdef INET_CSK_CLEAR_TIMERS
 		sk_stop_timer(sk, &icsk->icsk_delack_timer);
@@ -229,11 +229,12 @@ static inline void inet_csk_reset_xmit_timer(struct sock *sk, const int what,
 
 	if (what == ICSK_TIME_RETRANS || what == ICSK_TIME_PROBE0 ||
 	    what == ICSK_TIME_LOSS_PROBE || what == ICSK_TIME_REO_TIMEOUT) {
-		icsk->icsk_pending = what;
+		smp_store_release(&icsk->icsk_pending, what);
 		icsk->icsk_timeout = jiffies + when;
 		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 	} else if (what == ICSK_TIME_DACK) {
-		icsk->icsk_ack.pending |= ICSK_ACK_TIMER;
+		smp_store_release(&icsk->icsk_ack.pending,
+				  icsk->icsk_ack.pending | ICSK_ACK_TIMER);
 		icsk->icsk_ack.timeout = jiffies + when;
 		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 	} else {
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 2c5632d4fddb..12e975ed4910 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -775,7 +775,8 @@ void inet_csk_clear_xmit_timers(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
-	icsk->icsk_pending = icsk->icsk_ack.pending = 0;
+	smp_store_release(&icsk->icsk_pending, 0);
+	smp_store_release(&icsk->icsk_ack.pending, 0);
 
 	sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
 	sk_stop_timer(sk, &icsk->icsk_delack_timer);
@@ -790,7 +791,8 @@ void inet_csk_clear_xmit_timers_sync(struct sock *sk)
 	/* ongoing timer handlers need to acquire socket lock. */
 	sock_not_owned_by_me(sk);
 
-	icsk->icsk_pending = icsk->icsk_ack.pending = 0;
+	smp_store_release(&icsk->icsk_pending, 0);
+	smp_store_release(&icsk->icsk_ack.pending, 0);
 
 	sk_stop_timer_sync(sk, &icsk->icsk_retransmit_timer);
 	sk_stop_timer_sync(sk, &icsk->icsk_delack_timer);
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 67639309163d..321acc8abf17 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -247,6 +247,7 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 	struct nlmsghdr  *nlh;
 	struct nlattr *attr;
 	void *info = NULL;
+	u8 icsk_pending;
 	int protocol;
 
 	cb_data = cb->data;
@@ -307,14 +308,15 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 		goto out;
 	}
 
-	if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
-	    icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
-	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
+	icsk_pending = smp_load_acquire(&icsk->icsk_pending);
+	if (icsk_pending == ICSK_TIME_RETRANS ||
+	    icsk_pending == ICSK_TIME_REO_TIMEOUT ||
+	    icsk_pending == ICSK_TIME_LOSS_PROBE) {
 		r->idiag_timer = 1;
 		r->idiag_retrans = icsk->icsk_retransmits;
 		r->idiag_expires =
 			jiffies_delta_to_msecs(icsk->icsk_timeout - jiffies);
-	} else if (icsk->icsk_pending == ICSK_TIME_PROBE0) {
+	} else if (icsk_pending == ICSK_TIME_PROBE0) {
 		r->idiag_timer = 4;
 		r->idiag_retrans = icsk->icsk_probes_out;
 		r->idiag_expires =
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 5afe5e57c89b..985028434f64 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2900,15 +2900,17 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
 	__be32 src = inet->inet_rcv_saddr;
 	__u16 destp = ntohs(inet->inet_dport);
 	__u16 srcp = ntohs(inet->inet_sport);
+	u8 icsk_pending;
 	int rx_queue;
 	int state;
 
-	if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
-	    icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
-	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
+	icsk_pending = smp_load_acquire(&icsk->icsk_pending);
+	if (icsk_pending == ICSK_TIME_RETRANS ||
+	    icsk_pending == ICSK_TIME_REO_TIMEOUT ||
+	    icsk_pending == ICSK_TIME_LOSS_PROBE) {
 		timer_active	= 1;
 		timer_expires	= icsk->icsk_timeout;
-	} else if (icsk->icsk_pending == ICSK_TIME_PROBE0) {
+	} else if (icsk_pending == ICSK_TIME_PROBE0) {
 		timer_active	= 4;
 		timer_expires	= icsk->icsk_timeout;
 	} else if (timer_pending(&sk->sk_timer)) {
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 4fd746bd4d54..08772395690d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2960,7 +2960,7 @@ void tcp_send_loss_probe(struct sock *sk)
 		WARN_ONCE(tp->packets_out,
 			  "invalid inflight: %u state %u cwnd %u mss %d\n",
 			  tp->packets_out, sk->sk_state, tcp_snd_cwnd(tp), mss);
-		inet_csk(sk)->icsk_pending = 0;
+		smp_store_release(&inet_csk(sk)->icsk_pending, 0);
 		return;
 	}
 
@@ -2993,7 +2993,7 @@ probe_sent:
 
 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
 	/* Reset s.t. tcp_rearm_rto will restart timer from now */
-	inet_csk(sk)->icsk_pending = 0;
+	smp_store_release(&inet_csk(sk)->icsk_pending, 0);
 rearm_timer:
 	tcp_rearm_rto(sk);
 }
@@ -4224,7 +4224,8 @@ void tcp_send_delayed_ack(struct sock *sk)
 		if (!time_before(timeout, icsk->icsk_ack.timeout))
 			timeout = icsk->icsk_ack.timeout;
 	}
-	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
+	smp_store_release(&icsk->icsk_ack.pending,
+			  icsk->icsk_ack.pending | ICSK_ACK_SCHED | ICSK_ACK_TIMER);
 	icsk->icsk_ack.timeout = timeout;
 	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
 }
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 79064580c8c0..c3a7442332d4 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -361,6 +361,14 @@ static void tcp_delack_timer(struct timer_list *t)
 			from_timer(icsk, t, icsk_delack_timer);
 	struct sock *sk = &icsk->icsk_inet.sk;
 
+	/* Avoid taking socket spinlock if there is no ACK to send.
+	 * The compressed_ack check is racy, but a separate hrtimer
+	 * will take care of it eventually.
+	 */
+	if (!(smp_load_acquire(&icsk->icsk_ack.pending) & ICSK_ACK_TIMER) &&
+	    !READ_ONCE(tcp_sk(sk)->compressed_ack))
+		goto out;
+
 	bh_lock_sock(sk);
 	if (!sock_owned_by_user(sk)) {
 		tcp_delack_timer_handler(sk);
@@ -371,6 +379,7 @@ static void tcp_delack_timer(struct timer_list *t)
 			sock_hold(sk);
 	}
 	bh_unlock_sock(sk);
+out:
 	sock_put(sk);
 }
 
@@ -701,11 +710,11 @@ void tcp_write_timer_handler(struct sock *sk)
 		tcp_send_loss_probe(sk);
 		break;
 	case ICSK_TIME_RETRANS:
-		icsk->icsk_pending = 0;
+		smp_store_release(&icsk->icsk_pending, 0);
 		tcp_retransmit_timer(sk);
 		break;
 	case ICSK_TIME_PROBE0:
-		icsk->icsk_pending = 0;
+		smp_store_release(&icsk->icsk_pending, 0);
 		tcp_probe_timer(sk);
 		break;
 	}
@@ -717,6 +726,10 @@ static void tcp_write_timer(struct timer_list *t)
 			from_timer(icsk, t, icsk_retransmit_timer);
 	struct sock *sk = &icsk->icsk_inet.sk;
 
+	/* Avoid locking the socket when there is no pending event. */
+	if (!smp_load_acquire(&icsk->icsk_pending))
+		goto out;
+
 	bh_lock_sock(sk);
 	if (!sock_owned_by_user(sk)) {
 		tcp_write_timer_handler(sk);
@@ -726,6 +739,7 @@ static void tcp_write_timer(struct timer_list *t)
 			sock_hold(sk);
 	}
 	bh_unlock_sock(sk);
+out:
 	sock_put(sk);
 }
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index d71ab4e1efe1..7634c0be6acb 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -2177,6 +2177,7 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
 	const struct tcp_sock *tp = tcp_sk(sp);
 	const struct inet_connection_sock *icsk = inet_csk(sp);
 	const struct fastopen_queue *fastopenq = &icsk->icsk_accept_queue.fastopenq;
+	u8 icsk_pending;
 	int rx_queue;
 	int state;
 
@@ -2185,12 +2186,13 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
 	destp = ntohs(inet->inet_dport);
 	srcp  = ntohs(inet->inet_sport);
 
-	if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
-	    icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
-	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
+	icsk_pending = smp_load_acquire(&icsk->icsk_pending);
+	if (icsk_pending == ICSK_TIME_RETRANS ||
+	    icsk_pending == ICSK_TIME_REO_TIMEOUT ||
+	    icsk_pending == ICSK_TIME_LOSS_PROBE) {
 		timer_active	= 1;
 		timer_expires	= icsk->icsk_timeout;
-	} else if (icsk->icsk_pending == ICSK_TIME_PROBE0) {
+	} else if (icsk_pending == ICSK_TIME_PROBE0) {
 		timer_active	= 4;
 		timer_expires	= icsk->icsk_timeout;
 	} else if (timer_pending(&sp->sk_timer)) {
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index c2317919fc14..e85862352084 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3504,7 +3504,8 @@ static void schedule_3rdack_retransmission(struct sock *ssk)
 	timeout += jiffies;
 
 	WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER);
-	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
+	smp_store_release(&icsk->icsk_ack.pending,
+			  icsk->icsk_ack.pending | ICSK_ACK_SCHED | ICSK_ACK_TIMER);
 	icsk->icsk_ack.timeout = timeout;
 	sk_reset_timer(ssk, &icsk->icsk_delack_timer, timeout);
 }