[Openstack] Directional network performance issues with Neutron + OpenvSwitch
rick.jones2 at hp.com
Wed Oct 2 15:28:07 UTC 2013
On 10/02/2013 02:14 AM, James Page wrote:
> I tcpdump'ed the traffic and I see alot of duplicate acks which makes
> me suspect some sort of packet fragmentation but its got me puzzled.
> Anyone have any ideas about how to debug this further? or has anyone
> seen anything like this before?
Duplicate ACKs can be triggered by missing or out-of-order TCP segments.
Presumably that would show-up in the tcpdump trace though it might be
easier to see if you run the .pcap file through tcptrace -G.
Iperf may have a similar option, but if there are actual TCP
retransmissions during the run, netperf can be told to tell you about
them (when running under Linux):
netperf -H <remote> -t TCP_STREAM -- -o
will give to <remote>
netperf -H <remote> -t TCP_MAERTS -- -o
will give from <remote>. Or you can take snapshots of netstat -s output
from before and after your iperf run(s) and do the math by hand.
if the netperf in multiverse isn't new enough to grok the -o option, you
can grab the top-of-trunk from http://www.netperf.org/svn/netperf2/trunk
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