Unable to set socket size > 16MB

[Kevin Oberman]

I am trying to tune a FreeBSD system for ~100 ms. RTT at 10 Gbps. (I
posted another message about this back on 8/17). I am running current of
late July 31.

I am using iperf and I have confirmed (with gdb) that it is passing
setsockopt a size of 67108864 and setsockopt is returning 0. When I
capture the SYN packets, I am seeing a window of 64K and a scale
factor of 8. For 64 MB, the scale factor should be 10.

Is there some hidden limitation that would restrict this or is there a
bug involved? I have set net.inet.tcp.(send|recv)space to
64m. kern.ipc.maxsockbuf=134217728.

Here is the 3-way handshake:
13:57:45.571614 IP lbl.52460 > perf-bnl.commplex-link: S 4070670678:4070670678(0) win 65535 <mss 8960,nop,wscale 8,sackOK,timestamp 345761341 0>
13:57:45.665645 IP perf-bnl.commplex-link > lbl.52460: S 3909263475:3909263475(0) ack 4070670679 win 65535 <mss 8960,nop,wscale 8,nop,nop,timestamp 3623078172 345761341>
13:57:45.665683 IP lbl.52460 > perf-bnl.commplex-link: . ack 1 win 65535 <nop,nop,timestamp 345761435 3623078172>

Any reason for this? Any workaround or fix? Or am I missing something?
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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