[c-nsp] Transfer speed issues on 3560G

[Brandon Ewing]

This is a strange issue that I have noticed on a 3560G that we have
deployed.  We have two servers, on different ports, controlled by different
ASICs.  Each port negotiates a 1000mb/s link, but I cannot get more than
11MB/s (88mb/s) of traffic between the two ports.  I conducted the following
tests:

Transferring a 1GB file from one server to the other, written to /dev/null
Single transfer averaged 11.2MB/s

Performed two simultaneous transfers from one server to the other, written
to /dev/null.  One transfer completed at 2MB/s, the other at 9.3MB/s.  This
happens consistently, every test.

Performed two simultaneous transfers --  one between the two servers on the
switch, and one from another server off-switch to one of the servers.  Both
transfers maxed out at 11MB/s

This doesn't appear to be a TCP windowing issue, due to the fact that
doubling the number of TCP sessions did not result in a net increase of
overall speed.  It appears that any flow in between two ports can only reach
100mb/s.

Anyone have any idea where I can look to find the root cause? 

-- 
Brandon Ewing                                        (nicotine at warningg.com)
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