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Date: Mon, 03 Mar 2014 15:37:01 -0500 (EST)
From: David Miller <davem@...emloft.net>
To: ycheng@...gle.com
Cc: ncardwell@...gle.com, edumazet@...gle.com, nanditad@...gle.com,
netdev@...r.kernel.org
Subject: Re: [PATCH net] tcp: fix bogus RTT on special retransmission
From: Yuchung Cheng <ycheng@...gle.com>
Date: Fri, 28 Feb 2014 16:42:26 -0800
> RTT may be bogus with tall loss probe (TLP) when a packet
> is retransmitted and latter (s)acked without TCPCB_SACKED_RETRANS flag.
>
> For example, TLP calls __tcp_retransmit_skb() instead of
> tcp_retransmit_skb(). The skb timestamps are updated but the sacked
> flag is not marked with TCPCB_SACKED_RETRANS. As a result we'll
> get bogus RTT in tcp_clean_rtx_queue() or in tcp_sacktag_one() on
> spurious retransmission.
>
> The fix is to apply the sticky flag TCP_EVER_RETRANS to enforce Karn's
> check on RTT sampling. However this will disable F-RTO if timeout occurs
> after TLP, by resetting undo_marker in tcp_enter_loss(). We relax this
> check to only if any pending retransmists are still in-flight.
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
Applied, thank you.
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