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We've just installed gigabit switches at work, and things on the Linux side are going well. Our linux boxes, which use a Intel Corporation 82566DM-2 Gigabit nic (according to lspci), consistently get over 900 mbits/sec:

iperf -c ipserver
------------------------------------------------------------
Client connecting to ipserver, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.40.9 port 39823 connected with 192.168.1.115 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.08 GBytes    929 Mbits/sec

We have a bunch of Windows XP 64-bit machines that use Broadcom NetXtreme 57xx cards. I spent around a day trying to get equivalent speeds on them, but couldn't get above 200 Mbits/sec.

I noticed the Windows iperf tests said that the TCP window size was 8 Kb by default (as opposed to 16 Kb on Linux, so I modified my test to reflect that. Still no love.

I went to Broadcom's site, downloaded the latest drivers for the card and installed. Still no love. However, finally, I tried a 64 Kb window size with the new drivers, and finally an improvement!

$ iperf -c ipserver -w64k
------------------------------------------------------------
Client connecting to ipserver, TCP port 5001
TCP window size: 64.0 KByte
------------------------------------------------------------
[  3] local 192.168.40.214 port 1848 connected with 192.168.1.115 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec    933 MBytes    782 Mbits/sec

Much better, but still not really taking advantage of the full capabilities of the network. If the Linux box can reach 950 Mbits/sec consistently, this box should be able to as well.

Also, if you're wondering about the medium, this is over the same cable...I'm switching back and forth.

Any suggestion or ideas would be really welcome.

Thanks!

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run iperf -c ipserver -m on both machines. also, if the switches are smart look at the ports on the switch when the different machines are connected. –  dbasnett May 28 '10 at 13:53
    
are you dual booting between linux and xp, for test purposes? –  tony roth May 28 '10 at 15:38
    
Did you check anything comes default with wrong configuration in Broadcom's driver's "Advanced tab" ?. Device manager -> Broadcom NetXtreme > "Advanced" –  risyasin May 29 '10 at 9:31
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2 Answers

I would try booting the Windows machine with a bootable Linux CD like Ubuntu, and check the statistics there, to exclude the possible Hardware issues.

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How does booting to a live CD exclude the hardware? It's using the same hardware and infrastructure regardless of what OS is running. –  joeqwerty May 28 '10 at 17:24
    
If the OP gets the same results then he's excluded the OS, if he gets different (better) results then he's excluded the hardware (for the most part). The way your answer was worded didn't make sense to me. Sorry. –  joeqwerty May 28 '10 at 17:32
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Try getting a dedicated NIC that doesn't offload processing to the CPU. NewEgg sells a few OEM Intel cards for $25-40 that will do the trick.

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