Re: strange nonmonotonic behavior of gettimeoftheday

Manfred Spraul (
Fri, 02 Mar 2001 18:06:05 +0100

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> on AMD K6, VIA Technologies VT 82C586, Compaq Presario XL119.
> [snip]
> gives following result on box in question
> root@******:# ./clo
> Leap found: -1687 msec
> and prints nothing on all other my boxes.

Perhaps APM or SMI problems?
Could you run the attached program?

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#include <stdio.h> #include <sys/time.h> #include <unistd.h> #include <time.h>

static unsigned long long get_tsc(void) { unsigned long v1; unsigned long v2; __asm__ __volatile__( "rdtsc\n\t" : "=a" (v1), "=d" (v2)); return (((unsigned long long)v2)<<32)+v1; }

int main(int argc, char** argv) { unsigned long long t1; unsigned long long t2;

printf("RDTSC tester\n"); t1 = get_tsc(); for(;;) { t2 = get_tsc(); if(t1 > t2) { printf("tsc jumped backwards: from %lld to %lld.\n", t1, t2); } #if 0 printf("diff is %lld-%lld=%d.\n",t2,t1,t2-t1); #endif t1 = t2; } return 1; }


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