Negative ping times with FreeBSD 8.1-RELEASE on older Celeron system

Brett Glass brett at
Mon Sep 12 23:50:13 UTC 2011

More information regarding the odd behavior I'm seeing. Turns out
that packets do not even need to leave the machine for it to
report large negative ping times, on the order of more than half
a second. (See below.) Clearly something is odd about timekeeping
in this system (SiS motherboard chipset, PII-generation Celeron
but still effectively a "686") which was not a problem when it was
running FreeBSD 4.11-RELEASE (as it was before). What's more, it
appears that the negative ping times being shown for pings of
localhost are off by about -687 ms, consistently. Any ideas?
I am wondering if perhaps some recent change to the kernel
assumed that one would always have a faster CPU than the old
Celeron this machine is running, and that there is a race
condition or an error in the kernel code.

--Brett Glass

# ping localhost
PING localhost ( 56 data bytes
64 bytes from icmp_seq=0 ttl=64 time=-0.148 ms
64 bytes from icmp_seq=1 ttl=64 time=-0.151 ms
64 bytes from icmp_seq=2 ttl=64 time=-686.111 ms
64 bytes from icmp_seq=3 ttl=64 time=-0.180 ms
64 bytes from icmp_seq=4 ttl=64 time=0.110 ms
64 bytes from icmp_seq=5 ttl=64 time=686.351 ms
64 bytes from icmp_seq=6 ttl=64 time=-686.376 ms
64 bytes from icmp_seq=7 ttl=64 time=0.121 ms
64 bytes from icmp_seq=8 ttl=64 time=-686.402 ms
64 bytes from icmp_seq=9 ttl=64 time=-686.105 ms
64 bytes from icmp_seq=10 ttl=64 time=686.623 ms
64 bytes from icmp_seq=11 ttl=64 time=0.107 ms
64 bytes from icmp_seq=12 ttl=64 time=0.119 ms
64 bytes from icmp_seq=13 ttl=64 time=0.418 ms
64 bytes from icmp_seq=14 ttl=64 time=0.401 ms
64 bytes from icmp_seq=15 ttl=64 time=-0.169 ms
64 bytes from icmp_seq=16 ttl=64 time=0.113 ms
64 bytes from icmp_seq=17 ttl=64 time=0.401 ms
64 bytes from icmp_seq=18 ttl=64 time=-686.117 ms
64 bytes from icmp_seq=19 ttl=64 time=0.115 ms
64 bytes from icmp_seq=20 ttl=64 time=0.111 ms

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