linux-kernel - [PATCH 4.7 035/184] tcp: cwnd does not increase in TCP YeAH

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Message-Id: <20160922174050.218977274@linuxfoundation.org>
Date:   Thu, 22 Sep 2016 19:39:29 +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, Artem Germanov <agermanov@...horfree.com>,
        Dmitry Adamushko <d.adamushko@...horfree.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.7 035/184] tcp: cwnd does not increase in TCP YeAH

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Artem Germanov <agermanov@...horfree.com>


[ Upstream commit db7196a0d0984b933ccf2cd6a60e26abf466e8a3 ]

Commit 76174004a0f19785a328f40388e87e982bbf69b9
(tcp: do not slow start when cwnd equals ssthresh )
introduced regression in TCP YeAH. Using 100ms delay 1% loss virtual
ethernet link kernel 4.2 shows bandwidth ~500KB/s for single TCP
connection and kernel 4.3 and above (including 4.8-rc4) shows bandwidth
~100KB/s.
   That is caused by stalled cwnd when cwnd equals ssthresh. This patch
fixes it by proper increasing cwnd in this case.

Signed-off-by: Artem Germanov <agermanov@...horfree.com>
Acked-by: Dmitry Adamushko <d.adamushko@...horfree.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/tcp_yeah.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/tcp_yeah.c
+++ b/net/ipv4/tcp_yeah.c
@@ -76,7 +76,7 @@ static void tcp_yeah_cong_avoid(struct s
 	if (!tcp_is_cwnd_limited(sk))
 		return;
 
-	if (tp->snd_cwnd <= tp->snd_ssthresh)
+	if (tcp_in_slow_start(tp))
 		tcp_slow_start(tp, acked);
 
 	else if (!yeah->doing_reno_now) {