I don't know the iperf internals very well. It could be possible it's waiting on the OS which is in turn waiting on the driver / hardware. MAYBE try bumping your buffer size and running longer than 10 seconds, such as 30 seconds. Also, what is the client CPU doing during the test? Perhaps set your packet size to 1400 bytes. If for some reason it's being fragmented at 1470 bytes it could really slow things down.
G ________________________________ From: Randy Buck [mailto:[email protected]] Sent: Tuesday, April 27, 2010 11:05 AM To: [email protected] Subject: [Iperf-users] UDP not sending at full rate Hi, I'm working on a wireless mesh network and am trying to use iperf to benchmark performance. I'm running into an issue that has been very troublesome to understand. I am using the following setup: OS: Ubuntu 9.10 Wireless chipset: Aetheros Wireless driver: ath5k (included in 9.10) Let me know if I've left anything out.... Here is how I am starting the server: iperf -s -u -p 4000 Here is what I am running on the client: iperf -u -fk -c 5.0.0.9 -b 10000K -p 4000 -t 10 Note that I understand that the bandwidth is really 10 Mbps, I'm simply leaving in terms of Kbps for graphing purposes. Here is my output: ------------------------------------------------------------ Client connecting to 5.0.0.9, UDP port 4000 Sending 1470 byte datagrams UDP buffer size: 112 KByte (default) ------------------------------------------------------------ [ 3] local 5.0.0.5 port 38669 connected with 5.0.0.9 port 4000 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 8343 KBytes 6834 Kbits/sec [ 3] Sent 5812 datagrams [ 3] Server Report: [ 3] 0.0-10.1 sec 8137 KBytes 6631 Kbits/sec 0.698 ms 143/ 5811 (2.5%) [ 3] 0.0-10.1 sec 1 datagrams received out-of-order My concern is that I am not sending at 10 Mbps, but rather at 6.8 Mbps. I need to be able to send at 10 Mbp; I don't care what the packet loss is, I just need to be able to see what it is in terms of what I configured iperf to send at (10 Mbps). When I run over the wired network, I get what I expect (namely that I always send at the correct sending rate). The send rate is much higher for the wired network: Here is how I am starting the server: iperf -s -u -p 4000 Here is what I am running on the client: iperf -u -fk -c mesh9 -b 200000K -p 4000 -t 10 ------------------------------------------------------------ Client connecting to mesh9, UDP port 4000 Sending 1470 byte datagrams UDP buffer size: 112 KByte (default) ------------------------------------------------------------ [ 3] local 192.168.21.205 port 56030 connected with 192.168.21.209 port 4000 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 247418 KBytes 202684 Kbits/sec [ 3] Sent 172351 datagrams [ 3] Server Report: [ 3] 0.0-10.3 sec 117083 KBytes 93574 Kbits/sec 13.143 ms 90780/172340 (53%) [ 3] 0.0-10.3 sec 1 datagrams received out-of-order Why does iperf (or my wireless card, or my OS, or something else) not send at the full rate when transferring wirelessly? I'm beginning to believe that iperf is not the tool to use for wireless measurements. Are there any better solutions? Thanks for all your help, Randy
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