Intel Virtualization and clock_gettime reproducer

[Mr. Berkley Shands]

This affects every kernel I tried, 4.9.[54|35|24], 3.18.27, RH 3.10.0-693*.
The test machine is a Dell R740 with 2X8168 and 384GB.


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

inline long GetPerf()
{
   int _hi, _lo;
   __asm__ __volatile__ ("rdtsc":"=a" (_lo), "=d"(_hi));
   return ((long) _hi << 32) | _lo;
}

int main()
{

   struct timespec ts;
   int i, count;
   long start, end, delta, min, max, total, avg;

   count = 100;
   min = 0x7fffffff;
   max = 0;
   total = 0;

   for (i = 0; i < count; i++)
   {

      start = GetPerf();

      clock_gettime(CLOCK_REALTIME, &ts);

      end = GetPerf();

      delta = end - start;

      if (delta > max) max = delta;
      if (delta < min) min = delta;
      total += delta;
   }

   avg = total / count;

   printf("min: %ld\n", min);

--

//E. F. Berkley Shands, MSc
Senior Software Architect/Engineer
Exegy Systems Engineering//

**Exegy Inc.**

349 Marshall Road, Suite 100

St. Louis , MO 63119

Direct: (314) 218-3600 X450

Cell: (314) 303-2546

Office: (314) 218-3600

Fax: (314) 218-3601

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