Sawtooth ping RTT on RPi

[Peter Jeremy]

I've noticed a sawtooth-shaped cyclic pattern in ping RTTs to my RPi
(running r249590M):
64 bytes from 192.168.123.231: icmp_seq=22 ttl=64 time=1.321 ms
64 bytes from 192.168.123.231: icmp_seq=23 ttl=64 time=10.312 ms
64 bytes from 192.168.123.231: icmp_seq=24 ttl=64 time=9.328 ms
64 bytes from 192.168.123.231: icmp_seq=25 ttl=64 time=8.335 ms
64 bytes from 192.168.123.231: icmp_seq=26 ttl=64 time=7.411 ms
64 bytes from 192.168.123.231: icmp_seq=27 ttl=64 time=6.448 ms
64 bytes from 192.168.123.231: icmp_seq=28 ttl=64 time=5.497 ms
64 bytes from 192.168.123.231: icmp_seq=29 ttl=64 time=4.508 ms
64 bytes from 192.168.123.231: icmp_seq=30 ttl=64 time=3.540 ms
64 bytes from 192.168.123.231: icmp_seq=31 ttl=64 time=2.588 ms
64 bytes from 192.168.123.231: icmp_seq=32 ttl=64 time=1.635 ms
64 bytes from 192.168.123.231: icmp_seq=33 ttl=64 time=0.738 ms
64 bytes from 192.168.123.231: icmp_seq=34 ttl=64 time=9.770 ms
64 bytes from 192.168.123.231: icmp_seq=35 ttl=64 time=8.805 ms
64 bytes from 192.168.123.231: icmp_seq=36 ttl=64 time=7.833 ms
64 bytes from 192.168.123.231: icmp_seq=37 ttl=64 time=6.843 ms
64 bytes from 192.168.123.231: icmp_seq=38 ttl=64 time=5.869 ms

This doesn't appear with Linux (which has a RTT of 0.42ms with
very little variance).

What is causing the RTT pattern on FreeBSD?
Haw does Linux manage to respond so much faster?

-- 
Peter Jeremy
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