Messages in this thread | | | Date | Tue, 22 Apr 2003 17:23:16 -0600 | From | Trammell Hudson <> | Subject | gettimeofday running backwards on 2.4.20 |
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[ 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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