From: fuyuanli <fuyuanli@xxxxxxxxxxxxxx>
[ Upstream commit 30c6f0bf9579debce27e45fac34fdc97e46acacc ]
In this patch, we mainly try to handle sending a compressed ack
correctly if it's deferred.
Here are more details in the old logic:
When sack compression is triggered in the tcp_compressed_ack_kick(),
if the sock is owned by user, it will set TCP_DELACK_TIMER_DEFERRED
and then defer to the release cb phrase. Later once user releases
the sock, tcp_delack_timer_handler() should send a ack as expected,
which, however, cannot happen due to lack of ICSK_ACK_TIMER flag.
Therefore, the receiver would not sent an ack until the sender's
retransmission timeout. It definitely increases unnecessary latency.
Fixes: 5d9f4262b7ea ("tcp: add SACK compression")
Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: fuyuanli <fuyuanli@xxxxxxxxxxxxxx>
Signed-off-by: Jason Xing <kerneljasonxing@xxxxxxxxx>
Link: https://lore.kernel.org/netdev/20230529113804.GA20300@didi-ThinkCentre-M920t-N000/
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230531080150.GA20424@didi-ThinkCentre-M920t-N000
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/net/tcp.h | 1 +
net/ipv4/tcp_input.c | 2 +-
net/ipv4/tcp_timer.c | 16 +++++++++++++---
3 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 76bf0a11bdc77..99c74fc300839 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -632,6 +632,7 @@ void tcp_reset(struct sock *sk, struct sk_buff *skb);
void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb);
void tcp_fin(struct sock *sk);
void tcp_check_space(struct sock *sk);
+void tcp_sack_compress_send_ack(struct sock *sk);
/* tcp_timer.c */
void tcp_init_xmit_timers(struct sock *);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 10776c54ff784..dee174c40e874 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4530,7 +4530,7 @@ static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
}
}
-static void tcp_sack_compress_send_ack(struct sock *sk)
+void tcp_sack_compress_send_ack(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index cb79127f45c34..0b5d0a2867a8c 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -290,9 +290,19 @@ static int tcp_write_timeout(struct sock *sk)
void tcp_delack_timer_handler(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
- if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
- !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
+ if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
+ return;
+
+ /* Handling the sack compression case */
+ if (tp->compressed_ack) {
+ tcp_mstamp_refresh(tp);
+ tcp_sack_compress_send_ack(sk);
+ return;
+ }
+
+ if (!(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
return;
if (time_after(icsk->icsk_ack.timeout, jiffies)) {
@@ -312,7 +322,7 @@ void tcp_delack_timer_handler(struct sock *sk)
inet_csk_exit_pingpong_mode(sk);
icsk->icsk_ack.ato = TCP_ATO_MIN;
}
- tcp_mstamp_refresh(tcp_sk(sk));
+ tcp_mstamp_refresh(tp);
tcp_send_ack(sk);
__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
}
--
2.39.2
