Some might find the new --trip-times option in iperf 2.0.14 useful. It uses
little's law to compute the effective end/end queue size. The calculation is the queue size = send rate * write2read latency. It's under the inP column. Note that the client and server clocks must be synchronized for this option to work.
An example:
[root@localhost iperf2-code]# src/iperf -s -i 1 -w 4M
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 8.00 MByte (WARNING: requested 4.00 MByte)
------------------------------------------------------------
[ 4] local 192.168.1.4 port 5001 connected with 192.168.1.1 port 43158 (WARN: winsize=8.00 MByte req=4.00 MByte) (trip-times) (1580858380.423534)
[ ID] Interval Transfer Bandwidth Reads Dist(bin=16.0K) Burst Latency avg/min/max/stdev (cnt/size) inP NetPwr
[ 4] 0.00-1.00 sec 38.8 MBytes 326 Mbits/sec 1174 346:223:215:303:74:7:6:0 47.585/ 7.006/119.725/17.335 ms (310/131397) 1.92 MByte 856.01
[ 4] 1.00-2.00 sec 40.9 MBytes 343 Mbits/sec 1234 345:268:214:312:74:12:9:0 47.583/ 7.730/67.730/11.787 ms (328/130858) 1.96 MByte 902.05
[ 4] 2.00-3.00 sec 41.2 MBytes 346 Mbits/sec 1250 380:232:204:324:93:11:5:1 43.227/ 7.440/65.904/13.816 ms (330/131066) 1.78 MByte 1000.57
[ 4] 3.00-4.00 sec 41.3 MBytes 347 Mbits/sec 1249 384:226:218:322:85:8:5:1 44.932/ 6.927/66.840/12.453 ms (330/131310) 1.87 MByte 964.40
[ 4] 4.00-5.00 sec 41.0 MBytes 344 Mbits/sec 1240 344:257:243:296:86:6:7:1 44.778/ 5.779/66.241/13.478 ms (328/131140) 1.83 MByte 960.60
[ 4] 5.00-6.00 sec 41.2 MBytes 345 Mbits/sec 1244 379:228:226:319:72:11:7:2 47.515/ 6.943/66.759/11.371 ms (330/130808) 1.97 MByte 908.49
[ 4] 6.00-7.00 sec 41.4 MBytes 348 Mbits/sec 1250 361:246:236:308:81:12:5:1 46.300/ 5.783/66.702/12.341 ms (331/131264) 1.92 MByte 938.42
[ 4] 7.00-8.00 sec 41.4 MBytes 347 Mbits/sec 1254 366:254:230:293:92:12:7:0 45.072/ 8.689/66.511/12.084 ms (331/131054) 1.86 MByte 962.44
[ 4] 8.00-9.00 sec 41.3 MBytes 346 Mbits/sec 1269 370:263:223:328:76:7:2:0 48.664/12.814/67.439/10.563 ms (330/131136) 2.04 MByte 889.26
[ 4] 9.00-10.00 sec 41.3 MBytes 347 Mbits/sec 1262 386:234:231:310:86:9:6:0 48.086/ 8.675/66.493/11.122 ms (331/130971) 1.91 MByte 901.54
[ 4] 10.00-10.03 sec 937 KBytes 295 Mbits/sec 28 7:6:9:4:2:0:0:0 37.819/21.810/48.450/ 7.850 ms (8/119946) 89.9 MByte 976.33
[ 4] 0.00-10.03 sec 411 MBytes 344 Mbits/sec 12454 3668:2437:2249:3119:821:95:59:6 46.203/48.450/48.450/ 0.000 ms (3287/131072) 1.90 MByte 930.07
[root@localhost iperf2-code]# src/iperf -c 192.168.1.4 -w 4M -i 1 -e --trip-times
------------------------------------------------------------
Client connecting to 192.168.1.4, TCP port 5001 with pid 32598
Write buffer size: 128 KByte
TCP window size: 8.00 MByte (WARNING: requested 4.00 MByte)
------------------------------------------------------------
[ 3] local 192.168.1.1 port 43158 connected with 192.168.1.4 port 5001 (WARN: winsize=8.00 MByte req=4.00 MByte) (trip-times) (ct=3.49 ms)
[ ID] Interval Transfer Bandwidth Write/Err Rtry Cwnd/RTT NetPwr
[ 3] 0.00-1.00 sec 41.0 MBytes 344 Mbits/sec 328/0 0 5179K/26872 us 1599.87
[ 3] 1.00-2.00 sec 40.9 MBytes 343 Mbits/sec 327/0 0 5179K/30661 us 1397.88
[ 3] 2.00-3.00 sec 40.8 MBytes 342 Mbits/sec 326/0 0 5462K/23347 us 1830.19
[ 3] 3.00-4.00 sec 41.8 MBytes 350 Mbits/sec 334/0 0 5462K/20827 us 2101.99
[ 3] 4.00-5.00 sec 40.8 MBytes 342 Mbits/sec 326/0 0 5462K/23358 us 1829.33
[ 3] 5.00-6.00 sec 40.9 MBytes 343 Mbits/sec 327/0 0 5462K/20509 us 2089.84
[ 3] 6.00-7.00 sec 41.5 MBytes 348 Mbits/sec 332/0 0 5462K/19378 us 2245.63
[ 3] 7.00-8.00 sec 42.1 MBytes 353 Mbits/sec 337/0 0 5462K/23068 us 1914.83
[ 3] 8.00-9.00 sec 41.2 MBytes 346 Mbits/sec 330/0 0 5462K/23057 us 1875.95
[ 3] 9.00-10.00 sec 39.9 MBytes 334 Mbits/sec 319/0 0 5462K/6923 us 6039.57
[ 3] 0.00-10.02 sec 411 MBytes 344 Mbits/sec 3288/1 0 NA/0 us 0.00
Here's an example where the reads are rate limited to congest the end/end pipe
[root@localhost iperf2-code]# src/iperf -s -i 1 -w 4M -b 300m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 8.00 MByte (WARNING: requested 4.00 MByte)
------------------------------------------------------------
[ 4] local 192.168.1.4 port 5001 connected with 192.168.1.1 port 43162 (WARN: winsize=8.00 MByte req=4.00 MByte) (trip-times) (1580858757.457579)
[ ID] Interval Transfer Bandwidth Reads Dist(bin=16.0K) Burst Latency avg/min/max/stdev (cnt/size) inP NetPwr
[ 4] 0.00-1.00 sec 35.8 MBytes 300 Mbits/sec 734 178:122:118:149:29:6:4:128 66.196/11.050/127.404/25.372 ms (286/131072) 2.71 MByte 566.29
[ 4] 1.00-2.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 161.396/104.023/187.104/18.337 ms (286/131072) 6.13 MByte 232.27
[ 4] 2.00-3.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 172.448/149.679/187.410/ 8.933 ms (286/131072) 6.11 MByte 217.38
[ 4] 3.00-4.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 170.794/145.354/187.129/ 9.532 ms (286/131072) 6.12 MByte 219.48
[ 4] 4.00-5.00 sec 35.9 MBytes 301 Mbits/sec 287 0:0:0:0:0:0:0:287 167.554/119.285/187.002/12.842 ms (287/131072) 5.97 MByte 224.51
[ 4] 5.00-6.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 168.277/129.686/186.839/11.908 ms (286/131072) 6.07 MByte 222.77
[ 4] 6.00-7.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 164.621/118.836/188.298/14.838 ms (286/131072) 5.73 MByte 227.71
[ 4] 7.00-8.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 166.965/126.764/187.960/13.069 ms (286/131072) 5.94 MByte 224.52
[ 4] 8.00-9.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 169.325/131.557/189.220/11.436 ms (286/131072) 6.11 MByte 221.39
[ 4] 9.00-10.00 sec 35.8 MBytes 300 Mbits/sec 286 0:0:0:0:0:0:0:286 169.883/134.273/188.687/10.671 ms (286/131072) 6.15 MByte 220.66
[ 4] 10.00-10.17 sec 6.12 MBytes 297 Mbits/sec 49 0:0:0:0:0:0:0:49 153.230/121.217/175.104/13.653 ms (49/131072) 5.58 MByte 242.67
[ 4] 0.00-10.17 sec 364 MBytes 300 Mbits/sec 3358 178:122:118:149:29:6:4:2752 157.102/175.104/175.104/ 0.000 ms (2910/131072) 5.72 MByte 238.66
[root@localhost iperf2-code]# src/iperf -c 192.168.1.4 -w 4M -i 1 -e --trip-times
------------------------------------------------------------
Client connecting to 192.168.1.4, TCP port 5001 with pid 32618
Write buffer size: 128 KByte
TCP window size: 8.00 MByte (WARNING: requested 4.00 MByte)
------------------------------------------------------------
[ 3] local 192.168.1.1 port 43162 connected with 192.168.1.4 port 5001 (WARN: winsize=8.00 MByte req=4.00 MByte) (trip-times) (ct=3.29 ms)
[ ID] Interval Transfer Bandwidth Write/Err Rtry Cwnd/RTT NetPwr
[ 3] 0.00-1.00 sec 40.6 MBytes 341 Mbits/sec 325/0 0 4233K/26435 us 1611.44
[ 3] 1.00-2.00 sec 36.5 MBytes 306 Mbits/sec 292/0 0 4233K/15386 us 2487.52
[ 3] 2.00-3.00 sec 36.0 MBytes 302 Mbits/sec 288/0 0 4233K/15064 us 2505.89
[ 3] 3.00-4.00 sec 36.4 MBytes 305 Mbits/sec 291/0 0 4233K/17723 us 2152.12
[ 3] 4.00-5.00 sec 35.0 MBytes 294 Mbits/sec 280/0 0 4233K/15435 us 2377.72
[ 3] 5.00-6.00 sec 36.4 MBytes 305 Mbits/sec 291/0 0 4233K/14964 us 2548.91
[ 3] 6.00-7.00 sec 35.6 MBytes 299 Mbits/sec 285/0 0 4233K/15145 us 2466.52
[ 3] 7.00-8.00 sec 35.1 MBytes 295 Mbits/sec 281/0 0 4233K/16909 us 2178.20
[ 3] 8.00-9.00 sec 35.8 MBytes 300 Mbits/sec 286/0 0 4233K/17094 us 2192.97
[ 3] 9.00-10.00 sec 36.2 MBytes 304 Mbits/sec 290/0 0 4233K/19964 us 1903.97
[ 3] 0.00-10.03 sec 364 MBytes 304 Mbits/sec 2911/1 0 NA/0 us 0.00