Degraded performance when using GRE over tinc

[Loic Dachary]

Hi,

TL;DR: Upgrade to linux-3.13 to resolve the problem. It is not a tinc related problem.

A similar behavior was reported by James Page back in october 2013 http://www.gossamer-threads.com/lists/openstack/dev/31628?do=post_view_flat. Although I was not able to find a definitive answer, it hinted that the problem was related to a kernel bug. I was running a 3.11 kernel with OpenVSwitch 1.10.2. Upgrading to linux-3.13 with the in-tree version of OpenVSwitch resolved the problem. I switched back to 3.11 and OpenVSwitch 1.10.2 to check that the problems shows again and it did. The kernel upgrade has been verified to be the only modification. 

Cheers

On 29/04/2014 17:33, Loic Dachary wrote:
> It turns out that uploading with rsync works as fast as expected. The problem therefore seems to be : uploading works at 100Mb/s and downloading is degraded to 1Mb/s. Note that I checked that downloading on the same host without involving GRE or tinc indeed delivers 100Mb/s.
> 
> This is puzzling :-)
> 
> On 29/04/2014 16:31, Loic Dachary wrote:
>> Hi,
>>
>> In a setup where OpenVSwitch is used with GRE tunels on top of an interface provided by tinc, I'm experiencing significant performance degradation problems (from 100Mb/s down to 1Mb/s in the worst case) and I'm not sure how to fix this. The manifestation of the problem is, from the user point of view, iperf reports ~100Mb/s and rsync reports ~1Mb/s:
>>
>> $ iperf -c 91.224.149.132
>> ------------------------------------------------------------
>> Client connecting to 91.224.149.132, TCP port 5001
>> TCP window size: 23.5 KByte (default)
>> ------------------------------------------------------------
>> [  3] local 10.0.2.27 port 57143 connected with 91.224.149.132 port 5001
>> [ ID] Interval       Transfer     Bandwidth
>> [  3]  0.0-10.0 sec  99.4 MBytes  83.3 Mbits/sec
>>
>>
>> $ rsync --progress root at 91.224.149.132:precise-server-cloudimg-amd64-disk1.img .
>> precise-server-cloudimg-amd64-disk1.img
>>     32112640  12%   83.44kB/s    0:45:34
>>
>> A tcpdump of iperf ( http://dachary.org/loic/good.cap ) shows no retransmission while a tcpdump of rsync  ( http://dachary.org/loic/bad.cap ) shows a frequent "TCP Dup ACK", "TCP Retransmission", "TCP Out-Of-Order". 
>>
>> I'm not sure why this happens, any hint would be greatly appreciated :-)
>>
>> Cheers
>>
> 

-- 
Loïc Dachary, Artisan Logiciel Libre

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