netdev - Re: [PATCH net] tcp_bbr: fix to zero idle

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Message-Id: <20180502.111307.1740648414339763049.davem@davemloft.net>
Date:   Wed, 02 May 2018 11:13:07 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     ncardwell@...gle.com
Cc:     netdev@...r.kernel.org, ycheng@...gle.com, soheil@...gle.com,
        priyarjha@...gle.com, ysseung@...gle.com
Subject: Re: [PATCH net] tcp_bbr: fix to zero idle_restart only upon
 S/ACKed data

From: Neal Cardwell <ncardwell@...gle.com>
Date: Tue,  1 May 2018 21:45:41 -0400

> Previously the bbr->idle_restart tracking was zeroing out the
> bbr->idle_restart bit upon ACKs that did not SACK or ACK anything,
> e.g. receiving incoming data or receiver window updates. In such
> situations BBR would forget that this was a restart-from-idle
> situation, and if the min_rtt had expired it would unnecessarily enter
> PROBE_RTT (even though we were actually restarting from idle but had
> merely forgotten that fact).
> 
> The fix is simple: we need to remember we are restarting from idle
> until we receive a S/ACK for some data (a S/ACK for the first flight
> of data we send as we are restarting).
> 
> This commit is a stable candidate for kernels back as far as 4.9.
> 
> 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>
> Signed-off-by: Priyaranjan Jha <priyarjha@...gle.com>
> Signed-off-by: Yousuk Seung <ysseung@...gle.com>

Applied and queued up for -stable.