FAILED: patch "[PATCH] Revert "tcp: change pingpong threshold to 3"" failed to apply to 5.4-stable tree

From: Wei Wang <[email protected]>

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 <[email protected]>

Suggested-by Neal Cardwell <[email protected]>

Signed-off-by Wei Wang <[email protected]>

Acked-by Neal Cardwell <[email protected]>

Reviewed-by Eric Dumazet <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

From: Wei Wang <[email protected]>

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 <[email protected]>

Suggested-by Neal Cardwell <[email protected]>

Signed-off-by Wei Wang <[email protected]>

Acked-by Neal Cardwell <[email protected]>

Reviewed-by Eric Dumazet <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

---
  include/net/inet_connection_sock.h | 10 +---------
  net/ipv4/tcp_output.c              | 15 ++++++---------
  2 files changed, 7 insertions(+), 18 deletions(-)

include/net/inet_connection_sock.h +1 -9

index 13792c0ef46e..2e5f2c8b0663 100644
@@ -318,7 +318,7 @@ void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
 
  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)
  {

@@ -334,12 +334,4 @@ static inline bool inet_csk_in_pingpong_mode(struct sock *sk)
  {
  	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++;
-}
  #endif /* _INET_CONNECTION_SOCK_H */

net/ipv4/tcp_output.c +6 -9

index ef749a47768a..7f9004ae44a4 100644
@@ -166,16 +166,13 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
  	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. */

Quoted 6 lines · Kuniyuki Iwashima

From: Wei Wang <[email protected]>

commit 4d8f24eeedc58d5f87b650ddda73c16e8ba56559 upstream.

This reverts commit 4a41f453bedfd5e9cd040bad509d9da49feb3e2c.

Quoted 7 lines

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.

I would wait a bit before backporting this to stable:
https://lore.kernel.org/all/[email protected]/