The -w argument can only kindly request the operating system for a given socket buffer size. Then the operating system allocates whatever buffer size it wants. It's a pure operating system issue and iperf can do nothing about it. The actual TCP window size is limited by but not necessarily equal to socket buffer size of the receiver. It is constantly changing depending on the dynamics of the network. 2010/5/19 Peter George <peter.geo...@lumison.net>
> Hello, > > > > While doing some throughput testing, I was experimenting with fixed window > 256Kb sizes at both client and server end with the following flags; > > > > Linux Client [iperf version 2.0.4 (7 Apr 2008) pthreads] : ]#iperf -c > _SERVER_ -i5 -t60 -w 131072 > > Linux Server [iperf version 2.0.4 (7 Apr 2008) pthreads]: ]#iperf -s -w > 131072 > > > > I’m aware that Linux iPerf clients and servers double the –w switch for > Window size, and have observed this for window sizes smaller than 256Kb. > > > > However, when attempting to test 256Kb window sizes, I observed a > discrepancy at both client (214Kb) and server (224Kb) ends. Furthermore, > Tcpdump taken during the transfer, showed a maximum Window size achieved of > 170Kb. > > > > Can anyone explain why the –w switch did not let me achieve a 256Kb window > size in this case? > > > > Client, server, and Tcpdump output below; > > > > ------------------------------------------------------------ > > Client connecting to _SERVER_, TCP port 5001 > > TCP window size: *214 KByte* (WARNING: requested 128 KByte) > > ------------------------------------------------------------ > > [ 3] local 87.246.127.2 port 44874 connected with 87.246.83.2 port 5001 > > [ ID] Interval Transfer Bandwidth > > [ 3] 0.0- 5.0 sec 37.0 MBytes 62.1 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 5.0-10.0 sec 39.8 MBytes 66.8 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 10.0-15.0 sec 36.8 MBytes 61.7 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 15.0-20.0 sec 42.0 MBytes 70.5 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 20.0-25.0 sec 35.0 MBytes 58.7 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 25.0-30.0 sec 42.5 MBytes 71.3 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 30.0-35.0 sec 36.0 MBytes 60.5 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 35.0-40.0 sec 40.0 MBytes 67.2 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 40.0-45.0 sec 38.2 MBytes 64.1 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 45.0-50.0 sec 41.6 MBytes 69.9 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 50.0-55.0 sec 38.0 MBytes 63.7 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 55.0-60.0 sec 39.3 MBytes 65.9 Mbits/sec > > [ ID] Interval Transfer Bandwidth > > [ 3] 0.0-60.0 sec 466 MBytes 65.2 Mbits/sec > > > > ------------------------------------------------------------ > > Server listening on TCP port 5001 > > TCP window size: *224 KByte* (WARNING: requested 128 KByte) > > ------------------------------------------------------------ > > [ 4] local 87.246.83.2 port 5001 connected with 87.246.127.2 port 44874 > > [ ID] Interval Transfer Bandwidth > > [ 4] 0.0-60.0 sec 466 MBytes 65.2 Mbits/sec > > > > 135059 2010-04-20 10:09:37.266170 87.246.83.2 87.246.127.2 > TCP commplex-link > 44874 [ACK] Seq=1 Ack=377541609 *Win=170592* Len=0 > TSV=79744062 TSER=3433290552 > > > > > > Many thanks, > > > > P > > > > -- > > Peter George > > Network Administrator > > Lumison > > D: 0131 514 4022 > > T: 0845 1199 900 > > www.lumison.net > > > > P.S. do you love Lumison? Why not take a moment and vote for us? > > http://bit.ly/Vote_Lumison > > > > ------------------------------ > -- > > This email and any files transmitted with it are confidential and intended > solely for the use of the individual or entity to whom they are addressed. > If you have received this email in error please notify the sender. Any > offers or quotation of service are subject to formal specification. > Errors and omissions excepted. Please note that any views or opinions > presented in this email are solely those of the author and do not > necessarily represent those of Lumison. > Finally, the recipient should check this email and any attachments for the > presence of viruses. Lumison accept no liability for any > damage caused by any virus transmitted by this email. > > > ------------------------------------------------------------------------------ > > > _______________________________________________ > Iperf-users mailing list > Iperf-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/iperf-users > >
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