netdev - [PATCH] tcp: cwnd does not increase in TCP YeAH

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Date:   Sun, 4 Sep 2016 21:03:27 -0700
From:   Artem Germanov <agermanov@...horfree.com>
To:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <nanditad@...gle.com>, <edumazet@...gle.com>,
        <ncardwell@...gle.com>, <ycheng@...gle.com>
Subject: [PATCH] tcp: cwnd does not increase in TCP YeAH

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>
---
--- net/ipv4/tcp_yeah.c.orig    2016-09-04 09:53:01.000000000 -0700
+++ net/ipv4/tcp_yeah.c 2016-09-04 09:53:40.000000000 -0700
@@ -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) {