Hi,

Just an FYI for those who might be interested.  We added RTT and CWND samples in iperf 2.0.8 for the TCP transmitter (iperf client) as well as UDP mean/min/max/stdev in the iperf server (assumes the clocks are synched.)   Also, much faster sampling is supported.  These may be helpful to those trying to improve wi-fi performance. To get the output one needs to use the –e option.  Also, RTT/CWND is linux only.   Apple is evaluating the change set and *may* ship it with future phones and Mac OS X systems. 

Full change set here:

• Fix portability, compile and tested with Linux, Win10, Win7, WinXP, MacOS and Android
• Require -u for UDP (-b no longer defaults to UDP)
• Improved performance
• Enhanced reporting with -e
• Support smaller report intervals (5 ms or greater)
• Support SO_RCVTIMEOUT for server reports regardless of no packets
• Server will close the socket after no received traffic per the -t value (default is 10 sec)
• Support SO_TIMESTAMP for kernel level packet timestamping
• Support end/end latency in mean/min/max/stdev format (UDP) (-e required)
• (assumes client and server clocks synched, e.g by Precision Time Protocol)
• Add local port to bind support (-B option) using colon as separator
• (e.g. iperf -c 192.168.100.100 -B 192.168.100.10:6001)
• Support TCP rate limited streams (via the -b) using token bucket
• Support packets per second (UDP) via pps as units, (e.g. -b 1000pps)
• Display PPS in both client and server reports (UDP) (-e required)
• Support realtime scheduler as a command line option (--realtime or -z, assumes proper user privileges)
• Improve client tx code path so actual tx offered rate will converge to the -b value
• Improve accuracy of microsecond delay calls (in platform independent manner)
• (Use of Kalman filter to predict delay errors and adjust delays per predicted error)
• Display target loop time in initial client header (UDP)
• Fix final latency report sent from server to client (UDP)
• Include standard deviation in latency output
• Suppress unrealistic latency output using (-/-/-/-)
• Support SO_SNDTIMEO on send so socket write won't block beyond -t (TCP)
• Use clock_gettime if available (preferred over gettimeofday())
• TCP write and error counts (TCP retries and CWND for linux) (-e required)
• TCP read count, TCP read histogram (8 bins) (-e required)
• TCP RTT and CWND values in client reports (-e required, Linux only, RTT units microseconds)

Bob McMahon

Broadcom Wi-Fi QA Engineer