Re: udp performance on Windows XP

To: iperf-users --at-- dast.nlanr.net
Subject: Re: udp performance on Windows XP
From: Kevin Gibbs <kgibbs --at-- ncsa.uiuc.edu>
Date: Tue, 9 Dec 2003 10:06:06 -0600 (CST)
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In-reply-to: <77EBF06B.63E0E979.032A1F23 --at-- netscape.net>
Reply-to: iperf-users --at-- dast.nlanr.net
Sender: owner-iperf-users --at-- dast.nlanr.net

On Mon, 8 Dec 2003, lilyco wrote:
> Hi, has anyone ever met such problem that, on Windows XP, the UDP 
> sending rate of Iperf is very slow?
> 
> I have 2 machines connected by 1GigE link. Both have 2 2.4G Xeon CPU, 
> and one is running Linux, the other is running XP. When I test UDP 
> performance between these 2 machines, the throughput from Linux to XP is 
> very good, but the reverse direction can only reach about 50Mbps. The 
> TCP throughputs are both very well on two directions.
> 
> Any ideas?
> 
> Thanks a lot,
> Gu

You may be experiencing the lack of granularity of the 
GetSystemTimeAsFileTime on Win32 which is used for the replacement of 
gettimeofday which Win32 does not implement. This function has a large 
granularity 10ms, I believe, where gettimeofday on most *nixs will get you 
around a granularity of 10us. Unfortunately we have not had the time to 
rewrite the gettimeofday replacement for Win32 to use a Win32 Performance 
Timer rather than the GetSystemTimeAsFileTime function.

Kevin

References:
- udp performance on Windows XP
  - From: netlilyco --at-- netscape.net (lilyco)

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