[Bug 254695] Hyper-V + TCP_BBR: Kernel Panic: Assertion in_epoch(net_epoch_preempt) failed at netinet/tcp_lro.c:1180

From: <bugzilla-noreply_at_freebsd.org>
Date: Thu, 26 Aug 2021 12:30:22 UTC 
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254695

--- Comment #39 from Gordon Bergling <gbe@FreeBSD.org> ---
(In reply to Michael Tuexen from comment #38)

I tested D31679 and haven't system is running stable. I did some iperf3 testing
and the performance is somewhat strange when enabling TCP BBR. With the default
stack I got

[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   268 MBytes  2.24 Gbits/sec  4646   78.4 KBytes
[  5]   1.00-2.00   sec   304 MBytes  2.55 Gbits/sec  5520   85.5 KBytes
[  5]   2.00-3.00   sec   305 MBytes  2.56 Gbits/sec  5474    106 KBytes
[  5]   3.00-4.00   sec   311 MBytes  2.61 Gbits/sec  5705   1.41 KBytes
[  5]   4.00-5.00   sec   303 MBytes  2.54 Gbits/sec  5565   71.3 KBytes
[  5]   5.00-6.00   sec   305 MBytes  2.56 Gbits/sec  5474   88.4 KBytes
[  5]   6.00-7.00   sec   302 MBytes  2.53 Gbits/sec  5566   78.4 KBytes
[  5]   7.00-8.00   sec   287 MBytes  2.41 Gbits/sec  5198   65.6 KBytes
[  5]   8.00-9.00   sec   309 MBytes  2.60 Gbits/sec  5566   67.1 KBytes
[  5]   9.00-10.00  sec   297 MBytes  2.49 Gbits/sec  5520   65.6 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  2.92 GBytes  2.51 Gbits/sec  54234             sender
[  5]   0.00-10.00  sec  2.92 GBytes  2.51 Gbits/sec                  receiver


and with TCP BBR

[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.02   sec  22.4 MBytes   183 Mbits/sec  806   17.0 KBytes
[  5]   1.02-2.00   sec  8.48 KBytes  71.1 Kbits/sec    4   17.0 KBytes
[  5]   2.00-3.01   sec  0.00 Bytes  0.00 bits/sec    2   17.0 KBytes
[  5]   3.01-4.02   sec  2.83 KBytes  23.1 Kbits/sec    1   17.0 KBytes
[  5]   4.02-5.05   sec  2.83 KBytes  22.5 Kbits/sec    2   17.0 KBytes
[  5]   5.05-6.05   sec  0.00 Bytes  0.00 bits/sec    0   17.0 KBytes
[  5]   6.05-7.05   sec  2.83 KBytes  23.2 Kbits/sec    1   17.0 KBytes
[  5]   7.05-8.05   sec  0.00 Bytes  0.00 bits/sec    0   17.0 KBytes
[  5]   8.05-9.02   sec  0.00 Bytes  0.00 bits/sec    1   17.0 KBytes
[  5]   9.02-10.04  sec  0.00 Bytes  0.00 bits/sec    0   17.0 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.04  sec  22.4 MBytes  18.7 Mbits/sec  817             sender
[  5]   0.00-10.04  sec  22.1 MBytes  18.4 Mbits/sec                  receiver


Tested from VM to VM on the same host.

But at least the panic is gone.

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