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Date:      Wed, 8 May 2013 18:59:01 +1000
From:      Peter Jeremy <peter@rulingia.com>
To:        freebsd-arm@freebsd.org
Subject:   Sawtooth ping RTT on RPi
Message-ID:  <20130508085901.GA90732@server.rulingia.com>

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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=3D22 ttl=3D64 time=3D1.321 ms
64 bytes from 192.168.123.231: icmp_seq=3D23 ttl=3D64 time=3D10.312 ms
64 bytes from 192.168.123.231: icmp_seq=3D24 ttl=3D64 time=3D9.328 ms
64 bytes from 192.168.123.231: icmp_seq=3D25 ttl=3D64 time=3D8.335 ms
64 bytes from 192.168.123.231: icmp_seq=3D26 ttl=3D64 time=3D7.411 ms
64 bytes from 192.168.123.231: icmp_seq=3D27 ttl=3D64 time=3D6.448 ms
64 bytes from 192.168.123.231: icmp_seq=3D28 ttl=3D64 time=3D5.497 ms
64 bytes from 192.168.123.231: icmp_seq=3D29 ttl=3D64 time=3D4.508 ms
64 bytes from 192.168.123.231: icmp_seq=3D30 ttl=3D64 time=3D3.540 ms
64 bytes from 192.168.123.231: icmp_seq=3D31 ttl=3D64 time=3D2.588 ms
64 bytes from 192.168.123.231: icmp_seq=3D32 ttl=3D64 time=3D1.635 ms
64 bytes from 192.168.123.231: icmp_seq=3D33 ttl=3D64 time=3D0.738 ms
64 bytes from 192.168.123.231: icmp_seq=3D34 ttl=3D64 time=3D9.770 ms
64 bytes from 192.168.123.231: icmp_seq=3D35 ttl=3D64 time=3D8.805 ms
64 bytes from 192.168.123.231: icmp_seq=3D36 ttl=3D64 time=3D7.833 ms
64 bytes from 192.168.123.231: icmp_seq=3D37 ttl=3D64 time=3D6.843 ms
64 bytes from 192.168.123.231: icmp_seq=3D38 ttl=3D64 time=3D5.869 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?

--=20
Peter Jeremy

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