netdev - Re: 3.14 regression: huge latency in read/select on tun

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Date:	Thu, 03 Apr 2014 09:52:26 +0200
From:	Ortwin Glück <odi@....ch>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: 3.14 regression: huge latency in read/select on tun

On 02.04.2014 18:42, Eric Dumazet wrote:
> You could post a tcpdump maybe ?

This is a dump from on the tun interface (traffic inside the tunnel).
It's an scp upload of a 2MB file. I aborted after a while when not much
progress was seen anymore, but you get the idea.

What I see:
- Frame 28: long delay because I had to enter the key password
- Frame 31: the packets seems to be out of order. It has a sequence
number that is far ahead of previously sent sequence no's. Some
duplicates and retransmissions follow. That pattern repeats randomly all
over the trace.
- from Frame 73 on: ping pong of ACKs and data, while the data is
delayed by ~200ms caused by the select(). The ping pong also shows that
there are virtually no packets in flight (see also Window size).

Download attachment "dump.pcapng" of type "application/octet-stream" (842792 bytes)