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Subjectgettimeofday running backwards on 2.4.20
[ Please cc hudson@osresearch.net on any replies.  Thank you! ]

A few months ago I noticed gettimeofday running backwards on
dual Pentium II and dual Pentium Pro systems with 2.4.18. Based
on postings made to linux-kernel in June of 2002, I upgraded
to 2.4.20 and the problem seemed to go away:

http://groups.google.com/groups?threadm=3D16DE83.3060409@tiscalinet.it

Just recently my NAS benchmarks and MPI latency tests showed bizarre
results, so I pulled out my test program and am seeing the same
problems again. It seems that roughly 50 in 1 million calls go
backwards, even with 2.4.20.

Occasionally it is 4295 seconds (very consistently that value),
but most of them are just a few microseconds backwards. No error
code is returned from the system call either. No NTP or rdate type
services are running.

My test program can be seen here:

http://www.swcp.com/~hudson/gettimeofday.c

Interestingly, it only happens on the compute nodes with NFS root.
The service node has booted from a local SCSI disk and is serving roughly
140 compute nodes without any timing bugs.

service:~/tflop-linux: ssh node-181 uname -a \; cat /proc/cpuinfo
Linux node-181 2.4.20 #73 SMP Mon Apr 21 14:06:49 MDT 2003 i686 unknown
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 3
model name : Pentium II (Klamath)
stepping : 2
cpu MHz : 333.356
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr
bogomips : 665.19

processor : 1
vendor_id : GenuineIntel
cpu family : 6
model : 3
model name : Pentium II (Klamath)
stepping : 2
cpu MHz : 333.356
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr
bogomips : 665.19

Trammell
--
-----|----- hudson@osresearch.net W 240-283-1700
*>=====[]L\ hudson@rotomotion.com M 505-463-1896
' -'-`- http://www.swcp.com/~hudson/ KC5RNF

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