netdev - Re: [PATCH net] tcp: restrict F-RTO to work-around broken middle-boxes

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Message-Id: <20170407.114511.2181178908974978179.davem@davemloft.net>
Date:   Fri, 07 Apr 2017 11:45:11 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ycheng@...gle.com
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, edumazet@...gle.com,
        soheil@...gle.com
Subject: Re: [PATCH net] tcp: restrict F-RTO to work-around broken
 middle-boxes

From: Yuchung Cheng <ycheng@...gle.com>
Date: Fri,  7 Apr 2017 11:42:05 -0700

> The recent extension of F-RTO 89fe18e44 ("tcp: extend F-RTO
> to catch more spurious timeouts") interacts badly with certain
> broken middle-boxes.  These broken boxes modify and falsely raise
> the receive window on the ACKs. During a timeout induced recovery,
> F-RTO would send new data packets to probe if the timeout is false
> or not. Since the receive window is falsely raised, the receiver
> would silently drop these F-RTO packets. The recovery would take N
> (exponentially backoff) timeouts to repair N packet losses.  A TCP
> performance killer.
> 
> Due to this unfortunate situation, this patch removes this extension
> to revert F-RTO back to the RFC specification.
> 
> Fixes: 89fe18e44f7e ("tcp: extend F-RTO to catch more spurious timeouts")
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thank you.