First, TCP is definitely not designed to work under such conditions.
For example, assumptions behind RTO calculation and fast retransmit
heuristics are violated.  However, in this particular case my first
guess is that you are being limited by "cwnd moderation," which was
the topic of recent discussion here.  Under persistent reordering,
cwnd moderation can inhibit the ability of cwnd to grow.

Thanks,
  -John


On Tue, Apr 26, 2011 at 2:00 PM, Dominik Kaspar [off-list ref] wrote:

Hi Eric,

Here are the tcpdump files for the first TSO-disabled experiment, in a
full version and a short version with only the first 10000 packets:

http://home.simula.no/~kaspar/static/mptcp-emu-wlan-hspa-01-tos0-exp1-full.pcap
http://home.simula.no/~kaspar/static/mptcp-emu-wlan-hspa-01-tos0-exp1-short.pcap

By the way, the packets are sent from the server (x.x.x.189) to the
client interfaces (x.x.x.74) and (x.x.x.216) with the following
pattern (which is a non-bursty 128-bit approximation of scheduling
with a 600:400 ratio over primary path 0 and secondary path 1):

0010010100101001010010100101001010010100101001010010100101001010
0101001010010100101001010010100101001010010100101001010010100101

Greetings,
Dominik

On Tue, Apr 26, 2011 at 7:10 PM, Eric Dumazet [off-list ref] wrote:

quoted

Le mardi 26 avril 2011 à 18:58 +0200, Dominik Kaspar a écrit :

quoted

Hi Eric,

On Mon, Apr 25, 2011 at 5:38 PM, Eric Dumazet [off-list ref] wrote:

quoted

Since you have at sender a rule to spoof destination address of packets,
you should make sure you dont send "super packets (up to 64Kbytes)",
because it would stress the multipath more than you wanted to. This way,
you send only normal packets (1500 MTU).

ethtool -K eth0 tso off
ethtool -K eth0 gso off

I am pretty sure it should help your (atypic) workload.

I made new experiments with the exact same multipath setup as before,
but disabled TSO and GSO on all involved Ethernet interfaces. However,
this did not seem to change much about TCP's behavior when packets are
striped over heterogeneous paths. You can see the results of four
20-minute experiments on this plot:

http://home.simula.no/~kaspar/static/mptcp-emu-wlan-hspa-01-tos0.png

Cheers,
Dominik

Hi Dominik

Any chance to have a pcap file from sender side, of say first 10.000
packets ?

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