linux-kernel - [PATCH 5.10 17/65] Revert "tcp: change pingpong threshold to 3"

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Date:   Mon,  1 Aug 2022 13:46:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, LemmyHuang <hlm3280@....com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 5.10 17/65] Revert "tcp: change pingpong threshold to 3"

From: Wei Wang <weiwan@...gle.com>

commit 4d8f24eeedc58d5f87b650ddda73c16e8ba56559 upstream.

This reverts commit 4a41f453bedfd5e9cd040bad509d9da49feb3e2c.

This to-be-reverted commit was meant to apply a stricter rule for the
stack to enter pingpong mode. However, the condition used to check for
interactive session "before(tp->lsndtime, icsk->icsk_ack.lrcvtime)" is
jiffy based and might be too coarse, which delays the stack entering
pingpong mode.
We revert this patch so that we no longer use the above condition to
determine interactive session, and also reduce pingpong threshold to 1.

Fixes: 4a41f453bedf ("tcp: change pingpong threshold to 3")
Reported-by: LemmyHuang <hlm3280@....com>
Suggested-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Wei Wang <weiwan@...gle.com>
Acked-by: Neal Cardwell <ncardwell@...gle.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Link: https://lore.kernel.org/r/20220721204404.388396-1-weiwan@google.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/net/inet_connection_sock.h |   10 +---------
 net/ipv4/tcp_output.c              |   15 ++++++---------
 2 files changed, 7 insertions(+), 18 deletions(-)

--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -317,7 +317,7 @@ void inet_csk_update_fastreuse(struct in
 
 struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu);
 
-#define TCP_PINGPONG_THRESH	3
+#define TCP_PINGPONG_THRESH	1
 
 static inline void inet_csk_enter_pingpong_mode(struct sock *sk)
 {
@@ -334,14 +334,6 @@ static inline bool inet_csk_in_pingpong_
 	return inet_csk(sk)->icsk_ack.pingpong >= TCP_PINGPONG_THRESH;
 }
 
-static inline void inet_csk_inc_pingpong_cnt(struct sock *sk)
-{
-	struct inet_connection_sock *icsk = inet_csk(sk);
-
-	if (icsk->icsk_ack.pingpong < U8_MAX)
-		icsk->icsk_ack.pingpong++;
-}
-
 static inline bool inet_csk_has_ulp(struct sock *sk)
 {
 	return inet_sk(sk)->is_icsk && !!inet_csk(sk)->icsk_ulp_ops;
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -167,16 +167,13 @@ static void tcp_event_data_sent(struct t
 	if (tcp_packets_in_flight(tp) == 0)
 		tcp_ca_event(sk, CA_EVENT_TX_START);
 
-	/* If this is the first data packet sent in response to the
-	 * previous received data,
-	 * and it is a reply for ato after last received packet,
-	 * increase pingpong count.
-	 */
-	if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
-	    (u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
-		inet_csk_inc_pingpong_cnt(sk);
-
 	tp->lsndtime = now;
+
+	/* If it is a reply for ato after last received
+	 * packet, enter pingpong mode.
+	 */
+	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
+		inet_csk_enter_pingpong_mode(sk);
 }
 
 /* Account for an ACK we sent. */