ndt-users list created

[Jason Zurawski <>]

Hi Bob/All;

As the other respondents have noted - tuning windows is a dark art.

I have heard some claims that windows 7 (in particular the server OS) 
has some bugs in its auto-tuning capabilities (I wasn't able to find 
reference to a paper I read on this unfortunately ...).  For small 
latencies (e.g. less than 8ms or so) autotuning does not enable fully, 
and the window size won't grow past 64K.  Even for small latency, this 
is horrid for performance.  E.g. the Bandwidth Delay Product (see a good 
writeup + calculator here: 
http://www.switch.ch/network/tools/tcp_throughput/index.html) to reach 
1Gbps on a 1ms latency network still has to be > 128K, (2ms is 256K, 
etc.).

One thing you can do is examine the results (specifically the more 
statistics/more details screens) after running on a windows client and 
see what the 'client window size' was observed to be.  See if your 
settings match reality if you changed them, or in the event that you 
didn't see what autotuning is doing to the buffers.

With regards to packets arriving out of order was this only seen when 
testing to windows machines?  Are those servers running any form of 'tcp 
offload' in the NIC card/drivers?

Hope this helps, good luck!

-jason

On 2/13/12 5:02 PM, thus spake Bob Gerdes:
> Greetings,
>
> We have been doing a series of NDT tests on one of our campuses, and
> found that there is inconsistent results between Linux systems and
> Windows (XP and 7) systems. We have used the recommendations from DrTCP
> (noted on fasterdata.es.net) and the psc.edu site. And the Windows
> results consistently look much worse than the Linux systems. Has anyone
> been able to get better results with Windows and could suggest specific
> configuration settings?
>
> One additional note is that there was a 1.5% of packets that arrived out
> of order.
>
> Any advice would be greatly appreciated.
> Thanks,
> Bob
>
> Bob Gerdes
> Office of Instructional and Research Technologies (OIRT)
> Office of Information Technology (OIT)
> Rutgers, The State University
> ASB Annex I, room 101G, Busch Campus
> 56 Bevier Road, Piscataway, NJ 08854
> Phone: (732) 445-1438 Fax: 445-5539
>
> > We followed this reference which talks about tuning Windows XP:
> > http://www.psc.edu/networking/projects/tcptune/
> > as well as this
> > http://fasterdata.es.net/fasterdata/host-tuning/
> >
> > Also, we ran DrTCP, rebooted and still the exact same results from my
> > XP machine...
> >
> > > using linux in room 313
> > >
> > > Camden-to-Camden:
> > > running 10s outbound test (client to server) . . . . . 898.23 Mb/s
> > > running 10s inbound test (server to client) . . . . . . 880.40 Mb/s
> > >
> > > Camden-to-Newark:
> > > running 10s outbound test (client to server) . . . . . 478.16 Mb/s
> > > running 10s inbound test (server to client) . . . . . . 518.90 Mb/s
> > >
> > > Camden-to-NB:
> > > running 10s outbound test (client to server) . . . . . 841.83 Mb/s
> > > running 10s inbound test (server to client) . . . . . . 834.33 Mb/s
> > >
> > > and, when we switch the PC next to Linux system in BSB 113 to 1Gb
> > > (uses Windows 7), we get:
> > >
> > > Camden-to-Camden:
> > > running 10s outbound test (client to server) . . . . . 272.50 Mb/s
> > > running 10s inbound test (server to client) . . . . . . 726.08 Mb/s
> > >
> > > Camden-to-Newark:
> > > running 10s outbound test (client to server) . . . . . 55.24 Mb/s
> > > running 10s inbound test (server to client) . . . . . . 219.61 Mb/s
> > >
> > > Camden-to-NB:
> > > running 10s outbound test (client to server) . . . . . 60.01 Mb/s
> > > running 10s inbound test (server to client) . . . . . . 229.60 Mb/s
> > >
> > > comparable to Windows XP at Gig speed.
> > >
> > > It must be WINDOWS? and, it's configuration?
> > >
> > > So, is there an optimal setting for a Windows machine that I could try?
> > >
> > > > With the 3 systems tested giving basically the same results, this
> > > > kind of eliminates the possibility of cable issues or port
> > > > malfunctioning as well as OS and NIC issues.
> > > >
> > > > The traffic shaping and receiver limited issue seem puzzling.
> > > > > > > From two linux servers, got the following:
> > > > > > >
> > > > > > > From Office System (165.230.105 subnet):
> > > > > > > Camden-to-Camden:
> > > > > > > running 10s outbound test (client to server) . . . . . 862.62 Mb/s
> > > > > > > running 10s inbound test (server to client) . . . . . . 850.73 Mb/s
> > > > > > >
> > > > > > > Camden-to-Newark:
> > > > > > > running 10s outbound test (client to server) . . . . . 574.44 Mb/s
> > > > > > > running 10s inbound test (server to client) . . . . . . 519.07 Mb/s
> > > > > > >
> > > > > > > Camden-to-NB:
> > > > > > > running 10s outbound test (client to server) . . . . . 846.37 Mb/s
> > > > > > > running 10s inbound test (server to client) . . . . . . 816.39 Mb/s
> > > > > > >
> > > > > > >
> > > > > > > From clamshell (165.230.99 subnet):
> > > > > > > Camden-to-Camden:
> > > > > > > running 10s outbound test (client to server) . . . . . 882.16 Mb/s
> > > > > > > running 10s inbound test (server to client) . . . . . . 891.93 Mb/s
> > > > > > >
> > > > > > > Camden-to-Newark:
> > > > > > > running 10s outbound test (client to server) . . . . . 490.35 Mb/s
> > > > > > > running 10s inbound test (server to client) . . . . . . 531.92 Mb/s
> > > > > > >
> > > > > > > Camden-to-NB:
> > > > > > > running 10s outbound test (client to server) . . . . . 838.58 Mb/s
> > > > > > > running 10s inbound test (server to client) . . . . . . 869.51 Mb/s
> > > > > > >
> > > > > > > The NDT servers that I used were:
> > > > > > > ndt-cam.rutgers.edu
> > > > > > > ndt-nwk.rutgers.edu
> > > > > > > ndt-nbp.rutgers.edu