netdev - [PATCH net v3 3/3] tcp_cubic: fix to use emulated Reno cwnd one RTT in the future

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240815214035.1145228-4-mrzhang97@gmail.com>
Date: Thu, 15 Aug 2024 16:40:35 -0500
From: Mingrui Zhang <mrzhang97@...il.com>
To: edumazet@...gle.com,
	davem@...emloft.net,
	ncardwell@...gle.com,
	netdev@...r.kernel.org
Cc: Mingrui Zhang <mrzhang97@...il.com>,
	Lisong Xu <xu@....edu>
Subject: [PATCH net v3 3/3] tcp_cubic: fix to use emulated Reno cwnd one RTT in the future

The original code estimates RENO snd_cwnd using the estimated 
RENO snd_cwnd at the current time (i.e., tcp_cwnd).

The patched code estimates RENO snd_cwnd using the estimated 
RENO snd_cwnd after one RTT (i.e., tcp_cwnd_next_rtt), 
because ca->cnt is used to increase snd_cwnd for the next RTT.

Fixes: 89b3d9aaf467 ("[TCP] cubic: precompute constants")
Signed-off-by: Mingrui Zhang <mrzhang97@...il.com>
Signed-off-by: Lisong Xu <xu@....edu>
---
v2->v3: Corrent the "Fixes:" footer content
v1->v2: Separate patches

 net/ipv4/tcp_cubic.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 7bc6db82de66..a1467f99a233 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -315,8 +315,11 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked)
 			ca->tcp_cwnd++;
 		}
 
-		if (ca->tcp_cwnd > cwnd) {	/* if bic is slower than tcp */
-			delta = ca->tcp_cwnd - cwnd;
+		/* Reno cwnd one RTT in the future */
+		u32 tcp_cwnd_next_rtt = ca->tcp_cwnd + (ca->ack_cnt + cwnd) / delta;
+
+		if (tcp_cwnd_next_rtt > cwnd) {  /* if bic is slower than Reno */
+			delta = tcp_cwnd_next_rtt - cwnd;
 			max_cnt = cwnd / delta;
 			if (ca->cnt > max_cnt)
 				ca->cnt = max_cnt;
-- 
2.34.1