Re: iperf takes a lot of CPU bandwidth

To: iperf-users --at-- dast.nlanr.net
Subject: Re: iperf takes a lot of CPU bandwidth
From: Yaniv Kaul <ykaul --at-- checkpoint.com>
Date: Thu, 01 May 2003 09:21:40 +0200
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I'm using it as a testing tool, of course.
I'm trying to QoS and give priority for another application, while loading the line a bit with iperf. I still think that if I'm using iperf for ~100K UDP connection, the busy cycles shouldn't be that CPU cycles consuming. Perhaps that's an enhancement, though. Thanks for the explanation.

Y.
Technology Specialist, QA.
Check Point Software Technologies.

Kevin Gibbs wrote:

First Iperf is a testing tool and is not designed to be used in 
conjunction with other high profile applications or in a production 
environment. Second Iperf attempts to send at constant bit rate with UDP 
tests. As such it can not rely on any built-in timers or sleep functions 
due to inaccuracy of these functions and lack of fine granularity (<1ms). 
Therefore Iperf uses busy waiting to provide as close to constant bit rate 
as possible. This busy waiting consumes CPU time. Once again Iperf is a 
testing tool not something to run in the background all the time.

Kevin

On Wed, 30 Apr 2003, Yaniv Kaul wrote:

I'm running iperf 1.7.0, on Linux (RH 7.2), as a client, connected with 
IPv4 to multicast, with '-b 100K'.
I was running another multicast application, and it seemed sluggish, so 
I looked at 'top' and saw that iperf was constantly taking loads of CPU 
bandwidth - 60% and more!
The VNC I was connecting through was taking ~25%, the video application 
a mere ~20%. How could iperf be taking so much cpu?

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