Re: Reason to drop packets
- more information is necessary
The two systems are interconnected point-to-point via ethernrt wire (
100Mbit /s ), the CPU utilization I see during the test is ~ 90 % (
using "top" command or system monitor ).
I start dropping packets when UDP bandwidt > 9Mbit / s.
- questions
You wrote : "using larger buffers may help this since there will be less
overhead", but what do you mean by buffer ? UDP buffer size or UDP packet
size ?
How can I know the lost packets number on outgoing interface queues ?
Thanks
----- Original Message -----
From: "Jon Dugan" <jdugan --at-- ncsa.uiuc.edu>
To: <iperf-users --at-- dast.nlanr.net>
Sent: Monday, February 23, 2004 10:01 PM
Subject: Re: Reason to drop packets
> On Mon, Feb 23, 2004 at 06:46:30PM +0100, onorati_m --at-- virgilio.it wrote:
> > Hi all!
> >
> > Could someone explain why Iperf really starts dropping packets?
> >
> > I mean, selecting the UDP mode, setting a UDP bandwidth value and the
> > number of bytes to be transmitted, why does Iperf show losses for higher
> > values of the UDP bandwdith rate?
> >
> > Is it a matter of CPU load or something related with the buffer sizes?
>
> Iperf using UDP doesn't drop packets per se, rather it will blindly
transmit
> at the specified rate and if there is contention for resources somewhere
in
> the system the data will be lost. Often it is CPU utilization that is
the
> culprit. What is the CPU utilization you see during the test? Using
larger
> buffers may help this since there will be less overhead.
>
> The other common cause of lost data with a UDP test is loss somewhere in
the
> network. How are the two systems interconnected?
>
> Jon
> --
> Jon Dugan | Senior Network Engineer, NCSA Network Research
> jdugan --at-- ncsa.uiuc.edu | 269 CAB, 605 E Springfield, Champaign, IL 61820
> 217-244-7715 | http://www.ncsa.uiuc.edu/~jdugan/
>