netdev - Re: [PATCH net] tcp_bbr: fix quantization code to not raise cwnd if not probing bandwidth

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Date:   Fri, 27 Sep 2019 20:39:19 +0200 (CEST)
From:   David Miller <davem@...emloft.net>
To:     yyd@...gle.com
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, ycheng@...gle.com,
        soheil@...gle.com, priyarjha@...gle.com
Subject: Re: [PATCH net] tcp_bbr: fix quantization code to not raise cwnd
 if not probing bandwidth

From: "Kevin(Yudong) Yang" <yyd@...gle.com>
Date: Thu, 26 Sep 2019 10:30:05 -0400

> There was a bug in the previous logic that attempted to ensure gain cycling
> gets inflight above BDP even for small BDPs. This code correctly raised and
> lowered target inflight values during the gain cycle. And this code
> correctly ensured that cwnd was raised when probing bandwidth. However, it
> did not correspondingly ensure that cwnd was *not* raised in this way when
> *not* probing for bandwidth. The result was that small-BDP flows that were
> always cwnd-bound could go for many cycles with a fixed cwnd, and not probe
> or yield bandwidth at all. This meant that multiple small-BDP flows could
> fail to converge in their bandwidth allocations.
> 
> Fixes: 383d470 ("tcp_bbr: fix bw probing to raise in-flight data for very small BDPs")

Always use 12 digits of significance for SHA1 IDs, there are already 6 digit conflicts.

> Signed-off-by: Kevin(Yudong) Yang <yyd@...gle.com>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Acked-by: Priyaranjan Jha <priyarjha@...gle.com>

Applied and queued up for -stable.