[Codel] Recent top-of-trunk netperf change

[Rick Jones]

On the off chance that netperf gets used as part of evaluating CoDel, 
I've enhanced the "demo mode" functionality to respond a bit more 
quickly to drops in available bandwidth.  Just checked-in the change to 
the top-of-trunk at http://www.netperf.org/svn/netperf2/trunk .

Normally, when the user tells netperf she wants output every N time 
units, netperf calculates and updates an estimate for how many work 
units (bytes transferred, transactions) would take place in that length 
of time.  It then checks the elapsed time after that many units of work 
have been performed to see if it is time to emit an interim result. 
This goes back to the days when a gettimeofday() call was relatively 
expensive (and it can remain so in some places, IIRC).

Now, if the demo interval is expressed as a negative number rather than 
a positive one, netperf will check elapsed time after each unit of work 
is performed (send and/or recv call).

"Why not just the interval timer?"  Because netperf must also run under 
Windows :)  And the granularity may not be what the user desires.  And 
it also means less worry about handling signals.

happy benchmarking,

rick jones

BTW, it would appear that one can add an HTB qdisc to an interface, and 
then change the speed at will.  There may still be some small quantity 
of disruption (need to check the packet traces) but it behaves much more 
nicely than causing an Ethernet interface to re-negotiate speed... and 
allows a much broader range of speeds as well.

For example, a speed change from 500 to 5 Mbit/s via HTB with the legacy 
demo mode:

raj at tardy:~/netperf2_trunk$ src/netperf -D 1 -H 192.168.1.3 -l 0 -- -m 1K
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 
192.168.1.3 () port 0 AF_INET : demo
Interim result:  510.28 10^6bits/s over 1.533 seconds ending at 
1335385826.970
Interim result:  508.96 10^6bits/s over 1.003 seconds ending at 
1335385827.972
Interim result:  508.75 10^6bits/s over 1.001 seconds ending at 
1335385828.974
Interim result:  509.28 10^6bits/s over 1.001 seconds ending at 
1335385829.975
Interim result:  508.92 10^6bits/s over 1.001 seconds ending at 
1335385830.975
Interim result:    6.54 10^6bits/s over 77.768 seconds ending at 
1335385908.743
Interim result:    4.74 10^6bits/s over 1.382 seconds ending at 
1335385910.125
Interim result:    4.97 10^6bits/s over 1.126 seconds ending at 
1335385911.251
Interim result:    4.92 10^6bits/s over 1.126 seconds ending at 
1335385912.378
Interim result:    5.53 10^6bits/s over 1.024 seconds ending at 
1335385913.401
Interim result:    4.50 10^6bits/s over 1.229 seconds ending at 
1335385914.630
^CRecv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

  87380  16384   1024    90.11      37.31

And now with the new mode:
raj at tardy:~/netperf2_trunk$ src/netperf -D -1 -H 192.168.1.3 -l 0 -- -m 1K
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 
192.168.1.3 () port 0 AF_INET : demo
Interim result:  503.91 10^6bits/s over 1.000 seconds ending at 
1335386002.740
Interim result:  509.18 10^6bits/s over 1.001 seconds ending at 
1335386003.741
Interim result:  509.35 10^6bits/s over 1.001 seconds ending at 
1335386004.742
Interim result:  507.00 10^6bits/s over 1.001 seconds ending at 
1335386005.743
Interim result:  509.35 10^6bits/s over 1.000 seconds ending at 
1335386006.743
Interim result:  298.03 10^6bits/s over 1.012 seconds ending at 
1335386007.755
Interim result:    4.97 10^6bits/s over 1.126 seconds ending at 
1335386008.882
Interim result:    4.98 10^6bits/s over 1.127 seconds ending at 
1335386010.008
Interim result:    4.98 10^6bits/s over 1.126 seconds ending at 
1335386011.135
Interim result:    4.98 10^6bits/s over 1.177 seconds ending at 
1335386012.312
Interim result:    4.98 10^6bits/s over 1.075 seconds ending at 
1335386013.387
^CRecv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

  87380  16384   1024    12.26     234.27


This is what an advertise change from 1000 to 10 looks like, under the 
new netperf mechanism:

raj at tardy:~/netperf2_trunk$ src/netperf -D -1 -H 192.168.1.3 -l 0 -- -m 1K
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 
192.168.1.3 () port 0 AF_INET : demo
Interim result:  941.69 10^6bits/s over 1.001 seconds ending at 
1335386264.055
Interim result:  941.50 10^6bits/s over 1.000 seconds ending at 
1335386265.055
Interim result:  941.66 10^6bits/s over 1.000 seconds ending at 
1335386266.055
Interim result:  941.47 10^6bits/s over 1.000 seconds ending at 
1335386267.055
Interim result:  939.56 10^6bits/s over 1.000 seconds ending at 
1335386268.055
Interim result:   84.82 10^6bits/s over 7.253 seconds ending at 
1335386275.309
Interim result:    9.41 10^6bits/s over 1.056 seconds ending at 
1335386276.364
Interim result:    9.41 10^6bits/s over 1.056 seconds ending at 
1335386277.420
Interim result:    9.42 10^6bits/s over 1.056 seconds ending at 
1335386278.476
Interim result:    9.41 10^6bits/s over 1.056 seconds ending at 
1335386279.531
Interim result:    9.41 10^6bits/s over 1.056 seconds ending at 
1335386280.587
Interim result:    9.42 10^6bits/s over 1.056 seconds ending at 
1335386281.643
^CRecv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

  87380  16384   1024    19.38     277.95

basically the link was down for a number of seconds, which forced TCP to 
back-off even more