netdev - [PATCH net 3/3] tcp_bbr: reset long-term bandwidth sampling on loss recovery undo

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Date:   Thu,  7 Dec 2017 12:43:32 -0500
From:   Neal Cardwell <ncardwell@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH net 3/3] tcp_bbr: reset long-term bandwidth sampling on loss recovery undo

Fix BBR so that upon notification of a loss recovery undo BBR resets
long-term bandwidth sampling.

Under high reordering, reordering events can be interpreted as loss.
If the reordering and spurious loss estimates are high enough, this
can cause BBR to spuriously estimate that we are seeing loss rates
high enough to trigger long-term bandwidth estimation. To avoid that
problem, this commit resets long-term bandwidth sampling on loss
recovery undo events.

Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Reviewed-by: Yuchung Cheng <ycheng@...gle.com>
Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
---
 net/ipv4/tcp_bbr.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index ab3ff14ea7f7..8322f26e770e 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -878,6 +878,7 @@ static u32 bbr_undo_cwnd(struct sock *sk)

 	bbr->full_bw = 0;   /* spurious slow-down; reset full pipe detection */
 	bbr->full_bw_cnt = 0;
+	bbr_reset_lt_bw_sampling(sk);
 	return tcp_sk(sk)->snd_cwnd;
 }

-- 
2.15.1.424.g9478a66081-goog