[Bug 251052] [sctp] Throughput becomes extremely low under load

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 22 Apr 2022 22:10:47 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=251052

bc979@lafn.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bc979@lafn.org

--- Comment #6 from bc979@lafn.org ---
I believe the iperf3 test case is incorrect.  I don't fine --nstreams
documented.  However, it does do something and it appears that it sends very
little data the first second and then none after that.  The output indicates
that it is only using 1 stream.  The proper argument for multiple streams is
-P.  Hear are the results using -P 1 when sending on a 100MB LAN between 2
13.1-RC3 systems:

test# iperf3 -c master --sctp -P 1
Connecting to host master, port 5201
[  5] local 10.0.1.235 port 52689 connected to 10.0.1.250 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  13.0 MBytes   109 Mbits/sec                  
[  5]   1.00-2.00   sec  11.2 MBytes  94.4 Mbits/sec                  
[  5]   2.00-3.00   sec  11.2 MBytes  93.9 Mbits/sec                  
[  5]   3.00-4.00   sec  11.2 MBytes  94.4 Mbits/sec                  
[  5]   4.00-5.00   sec  11.2 MBytes  94.4 Mbits/sec                  
[  5]   5.00-6.00   sec  11.2 MBytes  94.4 Mbits/sec                  
[  5]   6.00-7.00   sec  11.2 MBytes  94.4 Mbits/sec                  
[  5]   7.00-8.00   sec  11.2 MBytes  93.8 Mbits/sec                  
[  5]   8.00-9.00   sec  11.2 MBytes  94.4 Mbits/sec                  
[  5]   9.00-10.00  sec  11.2 MBytes  93.8 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.00  sec   114 MBytes  95.7 Mbits/sec                  sender
[  5]   0.00-10.02  sec   112 MBytes  94.2 Mbits/sec                  receiver

The results are as expected (Well a bit better than I expected actually).  Now
changing to -P 2 I get:

test# iperf3 -c master --sctp -P 2
Connecting to host master, port 5201
[  5] local 10.0.1.235 port 60452 connected to 10.0.1.250 port 5201
[  7] local 10.0.1.235 port 40730 connected to 10.0.1.250 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  9.12 MBytes  76.5 Mbits/sec                  
[  7]   0.00-1.00   sec  5.56 MBytes  46.7 Mbits/sec                  
[SUM]   0.00-1.00   sec  14.7 MBytes   123 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   1.00-2.00   sec  7.50 MBytes  62.9 Mbits/sec                  
[  7]   1.00-2.00   sec  3.75 MBytes  31.5 Mbits/sec                  
[SUM]   1.00-2.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   2.00-3.00   sec  5.69 MBytes  47.7 Mbits/sec                  
[  7]   2.00-3.00   sec  5.56 MBytes  46.7 Mbits/sec                  
[SUM]   2.00-3.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   3.00-4.00   sec  3.81 MBytes  32.0 Mbits/sec                  
[  7]   3.00-4.00   sec  7.44 MBytes  62.4 Mbits/sec                  
[SUM]   3.00-4.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   4.00-5.00   sec  7.62 MBytes  64.0 Mbits/sec                  
[  7]   4.00-5.00   sec  3.62 MBytes  30.4 Mbits/sec                  
[SUM]   4.00-5.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   5.00-6.00   sec  4.12 MBytes  34.6 Mbits/sec                  
[  7]   5.00-6.00   sec  7.12 MBytes  59.8 Mbits/sec                  
[SUM]   5.00-6.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   6.00-7.00   sec  3.69 MBytes  30.9 Mbits/sec                  
[  7]   6.00-7.00   sec  7.56 MBytes  63.4 Mbits/sec                  
[SUM]   6.00-7.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   7.00-8.00   sec  2.69 MBytes  22.5 Mbits/sec                  
[  7]   7.00-8.00   sec  8.50 MBytes  71.3 Mbits/sec                  
[SUM]   7.00-8.00   sec  11.2 MBytes  93.8 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   8.00-9.00   sec   192 KBytes  1.57 Mbits/sec                  
[  7]   8.00-9.00   sec  11.1 MBytes  92.8 Mbits/sec                  
[SUM]   8.00-9.00   sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[  5]   9.00-10.00  sec  0.00 Bytes  0.00 bits/sec                  
[  7]   9.00-10.00  sec  11.2 MBytes  94.4 Mbits/sec                  
[SUM]   9.00-10.00  sec  11.2 MBytes  94.4 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.00  sec  44.4 MBytes  37.3 Mbits/sec                  sender
[  5]   0.00-10.06  sec  42.7 MBytes  35.6 Mbits/sec                  receiver
[  7]   0.00-10.00  sec  71.4 MBytes  59.9 Mbits/sec                  sender
[  7]   0.00-10.06  sec  70.3 MBytes  58.7 Mbits/sec                  receiver
[SUM]   0.00-10.00  sec   116 MBytes  97.2 Mbits/sec                  sender
[SUM]   0.00-10.06  sec   113 MBytes  94.3 Mbits/sec                  receiver


It specifically indicates that there are two streams in use.  The sums seem to
be the same as for 1 stream.  However, the data transferred each second is
quite uneven.  I don't know if that is a feature or bug.  I suspect it is just
the way the buffering worked.

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