Re: iperf

[Gerrit Renker <gerrit@erg.abdn.ac.uk>]

Quoting Patrick:
|  Hi,
|  
|  Quick question on iperf and kernel 2.6.22 (official and exp DCCP tree).
|  I use 2 computers + 1 netembox in between
|  Here are iperf cmd lines I use :
|  on dccpServer : # iperf -s -Xdccp -l1424
|  on dccpClient : # iperf -c dccpServer -Xdccp -l1424 -t30

This iperf variant only sends at full/maximum speed, i.e. it will try aggressively
to stuff your link, until it is forced to slow down by the kernel. This generates
a lot of other problems - such as increase in delay, queue overflow etc.

I haven't done bandwidth tests during the last days, but if you are doing such tests
can you please compare with the constant-bitrate variant of iperf:

 * use original source 
   http://www.erg.abdn.ac.uk/users/gerrit/dccp/apps/iperf/zip/iperf-2.0.2.tar.gz
 * only needs patch #1 from
   http://www.erg.abdn.ac.uk/users/gerrit/dccp/apps/iperf/patches/
 
 * then try iteratively with the -b switch to increase the bandwidth, i.e.
    iperf -c dccpServer -l1424  -d -b1m		# 1Mbps CBR DCCP
    iperf -c dccpServer -l1424  -d -b5m         # 5Mbps
    iperf -c dccpServer -l1424  -d -b10m        # 10Mbps
  
Do you get a higher speed this way? If yes, then the low speeds are likely due to
queue overflow, otherwise there is another reason. There have been a lot of changes
in the netdev kernel, the test tree has not been changed.

|  
|  On 2.6.22 kernel:
|  Without netem rate control, iperf result is about 95.0 Mbits/sec
|  With netem rate control at 1024Kbits/sec, iperf result could be
|  10Kbits/sec or 30Kbits/sec...
|  
|  On 2.6.20 with Ian's patches:
|  Without netem rate control, iperf result is about 95.0 Mbits/sec
|  With netem rate control at 1024Kbits/sec, iperf result is about 950Kbits/sec.
|  
|  netem cmd lines: (I also tried with delay and loss turned on)
|  tc qdisc add dev eth0 root handle 1:0 tbf rate 1024kbit buffer 10000 limit 30000
|  tc qdisc add dev eth1 root handle 1:0 tbf rate 1024kbit buffer 10000 limit 30000
|  
|  Is anyone has a such low rate on 2.6.22 kernel? do you know why?
|  
|  regards,
|  Patrick.
|  
|  
|  On 17/07/07, Ian McDonald <ian.mcdonald@jandi.co.nz> wrote:
|  > On 7/18/07, ツ Leandro Sales <leandroal@gmail.com> wrote:
|  > > Hi,
|  > >
|  > >    I'm using iperf to make some DCCP tests and I'd like to know if it
|  > > is possible to make iperf client (with -c option) transmit packets
|  > > during certain duration and measure the throughput each x seconds.
|  > > I've used -t 3 (for instance) option, but iperf just connect, send
|  > > packets, show the results and finish its job. I'd like to continuous
|  > > take instant throughput for each x seconds, how to do this?
|  > >
|  > > []s
|  > > Leandro.
|  >
|  > From iperf --help
|  >   -i, --interval  #        seconds between periodic bandwidth reports
|  >
|  > I use this quite a bit and works perfectly. I've also modified iperf
|  > to run continuously if you need that capability - available from my
|  > web page.
|  >
|  > Ian
|  > --
|  > Web: http://wand.net.nz/~iam4/
|  > Blog: http://iansblog.jandi.co.nz
|  > WAND Network Research Group
|  > -
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