Date: Mon, 12 Sep 2011 17:50:08 -0600 From: Brett Glass <brett@lariat.net> To: questions@freebsd.org Subject: RE: Negative ping times with FreeBSD 8.1-RELEASE on older Celeron system Message-ID: <201109122350.RAA21916@lariat.net>
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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 (127.0.0.1): 56 data bytes 64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=-0.148 ms 64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=-0.151 ms 64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=-686.111 ms 64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=-0.180 ms 64 bytes from 127.0.0.1: icmp_seq=4 ttl=64 time=0.110 ms 64 bytes from 127.0.0.1: icmp_seq=5 ttl=64 time=686.351 ms 64 bytes from 127.0.0.1: icmp_seq=6 ttl=64 time=-686.376 ms 64 bytes from 127.0.0.1: icmp_seq=7 ttl=64 time=0.121 ms 64 bytes from 127.0.0.1: icmp_seq=8 ttl=64 time=-686.402 ms 64 bytes from 127.0.0.1: icmp_seq=9 ttl=64 time=-686.105 ms 64 bytes from 127.0.0.1: icmp_seq=10 ttl=64 time=686.623 ms 64 bytes from 127.0.0.1: icmp_seq=11 ttl=64 time=0.107 ms 64 bytes from 127.0.0.1: icmp_seq=12 ttl=64 time=0.119 ms 64 bytes from 127.0.0.1: icmp_seq=13 ttl=64 time=0.418 ms 64 bytes from 127.0.0.1: icmp_seq=14 ttl=64 time=0.401 ms 64 bytes from 127.0.0.1: icmp_seq=15 ttl=64 time=-0.169 ms 64 bytes from 127.0.0.1: icmp_seq=16 ttl=64 time=0.113 ms 64 bytes from 127.0.0.1: icmp_seq=17 ttl=64 time=0.401 ms 64 bytes from 127.0.0.1: icmp_seq=18 ttl=64 time=-686.117 ms 64 bytes from 127.0.0.1: icmp_seq=19 ttl=64 time=0.115 ms 64 bytes from 127.0.0.1: icmp_seq=20 ttl=64 time=0.111 ms
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