netdev - Re: [PATCH net 1/5] tcp_bbr: cut pacing rate only if filled pipe

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Message-ID: <20170714153646.1cdc5f00@xeon-e3>
Date:   Fri, 14 Jul 2017 15:36:46 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Yuchung Cheng <ycheng@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net 1/5] tcp_bbr: cut pacing rate only if filled pipe

On Fri, 14 Jul 2017 17:49:21 -0400
Neal Cardwell <ncardwell@...gle.com> wrote:

> In bbr_set_pacing_rate(), which decides whether to cut the pacing
> rate, there was some code that considered exiting STARTUP to be
> equivalent to the notion of filling the pipe (i.e.,
> bbr_full_bw_reached()). Specifically, as the code was structured,
> exiting STARTUP and going into PROBE_RTT could cause us to cut the
> pacing rate down to something silly and low, based on whatever
> bandwidth samples we've had so far, when it's possible that all of
> them have been small app-limited bandwidth samples that are not
> representative of the bandwidth available in the path. (The code was
> correct at the time it was written, but the state machine changed
> without this spot being adjusted correspondingly.)
> 
> Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control")
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>

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