freeBSD network performance abnormal when iperf -s as server testing,
Only normal about 1/10 ~ 1/5

Three test OS on the same vmware ESXi 6.0 update 2

FreeBSD11.0  IP 10.10.10.110
FreeBSD10.3  IP 10.10.10.103
RHEL66       IP 10.10.10.66

netowrk Cards are vmxnet3, these test OS all in the same ESXi host, the same vswitcher, the same subnet, otherwise no adjustment is installed by default

When FreeBSD running iperf as server : iperf -s

Any other client iperf -c 10.10.10.110 (FreeBSD 11.0 IP address)
Speed is generally 3.xG
Any other client iperf -c 10.10.10.103 (FreeBSD 10.3 IP address)
Speed is generally 7.xG

But RHEL66 run iperf as server: iperf -s
Any client iperf -c 10.10.10.66 (RHEL66 IP address)
Speeds of up to 30G, 38G highest

And then on another host ESXi6.0 update2 test, the situation is still,
FreeBSD run ipers -c as client ,speed can reach 38G
But FreeBSD 11.0 run iperf -s as server, the highest speed only 4G
But FreeBSD 10.3 run iperf -s as server, the highest speed only 8G

FreeBSD10.3 amd64 and i386 result same

test result:

root@freebsd103:~ # uname -a
FreeBSD freebsd103 10.3-RELEASE-p2 FreeBSD 10.3-RELEASE-p2 #0: Wed May  4 06:03:51 UTC 2016     root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
root@freebsd103:~ #
root@freebsd103:~ # iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 64.0 KByte (default)
------------------------------------------------------------
[  4] local 10.10.10.103 port 5001 connected with 10.10.10.66 port 38535
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  9.14 GBytes  7.85 Gbits/sec
^Croot@freebsd103:~ # iperf -c rhel66
------------------------------------------------------------
Client connecting to rhel66, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local 10.10.10.103 port 10056 connected with 10.10.10.66 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  45.2 GBytes  38.8 Gbits/sec
root@freebsd103:~ #