netdev - Re: [PATCH net] tcp: invalidate rate samples during SACK reneging

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Date:   Fri, 08 Dec 2017 10:07:31 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     ysseung@...gle.com
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH net] tcp: invalidate rate samples during SACK reneging

From: Yousuk Seung <ysseung@...gle.com>
Date: Thu,  7 Dec 2017 13:41:34 -0800

> Mark tcp_sock during a SACK reneging event and invalidate rate samples
> while marked. Such rate samples may overestimate bw by including packets
> that were SACKed before reneging.
> 
> < ack 6001 win 10000 sack 7001:38001
> < ack 7001 win 0 sack 8001:38001 // Reneg detected
>> seq 7001:8001 // RTO, SACK cleared.
> < ack 38001 win 10000
> 
> In above example the rate sample taken after the last ack will count
> 7001-38001 as delivered while the actual delivery rate likely could
> be much lower i.e. 7001-8001.
> 
> This patch adds a new field tcp_sock.sack_reneg and marks it when we
> declare SACK reneging and entering TCP_CA_Loss, and unmarks it after
> the last rate sample was taken before moving back to TCP_CA_Open. This
> patch also invalidates rate samples taken while tcp_sock.is_sack_reneg
> is set.
> 
> Fixes: b9f64820fb22 ("tcp: track data delivery rate for a TCP connection")
> Signed-off-by: Yousuk Seung <ysseung@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Priyaranjan Jha <priyarjha@...gle.com>

Applied and queued up for -stable.