Date: Sat, 4 Jan 2014 17:36:44 -0500 (EST) From: Garrett Wollman <wollman@hergotha.csail.mit.edu> To: peter@wemm.org Cc: freebsd-net@freebsd.org Subject: Re: Long-haul problems - connections stuck in slow start Message-ID: <201401042236.s04MaiBn026166@hergotha.csail.mit.edu> In-Reply-To: <CAGE5yCpK7N1BwzGCXmx=8M4Q4cu9iUKo4Za-92gRwnkR=HvAiA@mail.gmail.com> References: <52C85537.7080307@wemm.org> <52C85EED.801@wemm.org>
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In article <CAGE5yCpK7N1BwzGCXmx=8M4Q4cu9iUKo4Za-92gRwnkR=HvAiA@mail.gmail.com>, Peter Wemm writes: >I'm looking at the duplicate acks in this trace from each end.. any >clues where they're coming from? My original suggestion was going to be that they're probably a result of your packets getting reordered because of that path instability you pointed out. 10 ms differential delay is much higher than the interarrival time should be, so you likely have a burst of packets headed down the slow path, followed by a burst of packets down the fast path, and the later packets arrive at the destination first, causing a burst of dupacks until the slow packets catch up. But that doesn't seem to be born out by your traces. Do you have TCP RX offload on this hardware? Could it be sending the dupacks without looping them back to BPF? (I haven't looked at our TCP offload code so I have no idea if that's even possible.) -GAWollman
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