[RndTbl] NIC performance with iperf

Kevin McGregor kevin.a.mcgregor at gmail.com
Sat Apr 17 07:40:57 CDT 2010

Hmm. Now I'll have to do some tests at work next week using various
combinations of OS and VMware ESX/vSphere. I'll get back to you. :)

On Fri, Apr 16, 2010 at 3:36 PM, Adam Thompson <athompso at athompso.net>wrote:

> 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 at athompso.net>
>  (204) 291-7950
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> Roundtable at muug.mb.ca
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