FYI. Windows networking sucks, across all versions of Windows. (At least, at Gigabit speeds, it does.)
Between my Windows 7 PC (3.06Ghz HT Pentium 4, Intel PRO 1000/MT Desktop Adapter [82540EM]) and Gentoo Linux server (2 x 2.2GHz Xeon [P4 core], PCI-X [64-bit,66Mhz] Intel PRO 1000/MT Dual-Port Server Adapter [82546EB])
Using "iperf -s" and "iperf -c 192.168.x.x", I get - consistently - between 238Mbps and 250Mbps **in both directions**.
Interesting to note is that the Windows 7 PC is CPU-limited on both sending and receiving, despite having all the offload and acceleration features turned on. Simultaneously, the Gentoo box sees a spike on one CPU... to 1%.
In UDP traffic, however, I see a startling asymmetry: PC-to-Linux can only send UDP at ~50Mbps, Linux-to-PC sends UDP at ~475Mbps. WTF?
I also tried the Parallel option, which runs multiple streams in parallel. Results are consistent, aggregate bandwidth is still only about 260Mbps. Two streams pegs both logical (HT) CPUs on the client at ~95% utilization.
I tried enabling and disabling both the Windows Firewall and my AV software, which made essentially no difference at all.
Then I also tried running the same set of tests from a Windows 2003 R2 server (2 x 2.13GHz Athlon MP, PCI-X [64-bit,66Mhz] Broadcom NetXtreme [BCM57xx]) N.B. this is the same model of motherboard Kevin is using in his Linux server. and observed slightly better throughput to the Linux server: about 380Mbps. Still better was Linux-to-W2K3R2, at about 440Mbps. UDP performance was similar to Kevin's results, at 103Mbps W2K3-to-Linux & 950Mbps Linux-to-W2K3.
CPU utilization on the W2K3R2 box exhibited similar properties as the Win7 client, although none of the tests actually managed to max out either CPU, instead peaking at about 70% utilization.
Just for kicks, I ran a test between a RHEL5 VM (under VMWare ESXi 4.0U1, VMXNET adapter) and my Linux server... 920+ Mbps every time! Of course, that number may be suspect since the UDP test reports speeds of 45.3Gbps :-).
Conclusion: the culprit is the Windows networking stack. Note that W2K3R2 is supposed to support zero-copy TCP offload, theoretically allowing network communications at wirespeed with extremely low latency. So much for that idea...
-Adam Thompson athompso@athompso.net (204) 291-7950