/******************************************************
/*
/* consume ratio freq
/*         to consume cpu time at ratio and frequency.
/*         The original code was from Peter Zijlstra,
/*         the  kernal.org maintainer of the sched
/*         area of the kernel code.
/*
/* consume.c Smythies 2014.05.05
/*         Fix usage message.
/*
/* consume.c Smythies 2013.11.04
/*         Add a time to execute parameter.
/*         allow the fraction to be as low as 0.5 percent
/*
/* consume.c Smythies 2012.06.27
/*         More precision desired. Switch to doubles for
/*         run time parameters.
/*
/* consume.c Smythies 2012.06.23
/*         I think in frequency for this stuff, so change
/*         the run time parameter from period to frequency.
/*         Make it not optional.
/*
/* consume.c Smythies 2012.06.23
/*         First just try to compile the code as sent
/*         from Peter Zijlstra.
/*         But converted to my coding standards (which will
/*         annoy Peter if it ever gets sent back).
/*
/******************************************************/

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

unsigned long long stamp(void){
   struct timeval tv;

   gettimeofday(&tv, NULL);

   return (unsigned long long)tv.tv_sec * 1000000 + tv.tv_usec;
} /* endprocedure */

void consume(int spin, int total, int elapsed){
   unsigned long long begin, now, start, lelapsed;

   begin = stamp();
   start = begin;
   now = begin;
   lelapsed = (long long)(elapsed * 1000000);

   while((long long)(now - start) < lelapsed) {  /* for the requested time */
      now = stamp();
      if ((long long)(now - begin) > spin) {
         usleep(total - spin);
         begin += total;
      } /* endif */
   } /* endwhile */
} /* endprocedure */

int main(int argc, char **argv){
   double frac, freq, duration, period;

   printf("consume: %s %s %s\n", argv[1], argv[2], argv[3]);

   switch(argc){
   case 4:
      frac = atof(argv[1]);
      freq = atof(argv[2]);
      duration = atof(argv[3]);
      break;
   default:
      fprintf(stderr, "%s <frac> <freq> <duration>\n  frac   -- [0.5-100.0] %% of time to burn\n  freq -- [hz] (min 1.0) frequency of burn/sleep cycle\n duration -- [seconds] (0.0 means 1 day) time for program to run\n", argv[0]);
      return -1;
   } /* endcase */

/*   printf("consume: %lf %lf %lf\n", frac, freq, duration); /*  */
   if (frac > 100.0){
      frac = 100.0;
   } /* endif */
   if (frac < 0.50){
      frac = 0.50;
   } /* endif */
   if (freq < 1.0){
      freq = 1.0;
   } /* endif */
   if (duration <= 0.0){
      duration = 86400.0;
   } /* endif */
   period = 1000000.0 / freq;
/*   printf("consume: %lf %lf %lf %lf\n", frac, freq, period, duration); /*  */
   consume((int)(period * frac / 100.0 + 0.5), (int)(period + 0.5), (int)(duration + 0.5));
   return 0;
} /* endprocedure */