When CONFIG_HZ defaults to 1000Hz and the network transmission time is
less than 1ms, lsndtime and lrcvtime are likely to be equal, which will
lead to hundreds of interactions before entering pingpong mode.

Signed-off-by: LemmyHuang <hlm3280@163.com>
---
 net/ipv4/tcp_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 858a15cc2..35ed65f80 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -172,7 +172,7 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
 	 * and it is a reply for ato after last received packet,
 	 * increase pingpong count.
 	 */
-	if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
+	if ((tp->lsndtime <= icsk->icsk_ack.lrcvtime) &&
 	    (u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
 		inet_csk_inc_pingpong_cnt(sk);
 
-- 
2.27.0

On Tue, 19 Jul 2022 21:01:37 +0800 LemmyHuang wrote:
> -	if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
> +	if ((tp->lsndtime <= icsk->icsk_ack.lrcvtime) &&

Are you sure you don't need to take care of the values wrapping?
before() does that. You may want !after() if you want to allow equal.

At 2022-07-20 08:49:15, "Jakub Kicinski" <kuba@kernel.org> wrote:
> On Tue, 19 Jul 2022 21:01:37 +0800 LemmyHuang wrote:
>> -	if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
>> +	if ((tp->lsndtime <= icsk->icsk_ack.lrcvtime) &&
>
> Are you sure you don't need to take care of the values wrapping?
> before() does that. You may want !after() if you want to allow equal.

Yeap, I will switch to that in v2.
Thank you!