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

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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>
This commit is contained in:
Jakub Kicinski 2024-10-04 15:34:42 -07:00
commit 2f65168355
8 changed files with 49 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/net/inet_connection_sock.h
View File

@ -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 {

6
net/ipv4/inet_connection_sock.c
View File

@ -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);

10
net/ipv4/inet_diag.c
View File

@ -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 =

10
net/ipv4/tcp_ipv4.c
View File

@ -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)) {

7
net/ipv4/tcp_output.c
View File

@ -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 @@ void tcp_send_loss_probe(struct sock *sk)
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);
}

18
net/ipv4/tcp_timer.c
View File

@ -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);
}

10
net/ipv6/tcp_ipv6.c
View File

@ -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)) {

3
net/mptcp/protocol.c
View File

@ -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);
}