cpu_usage_as_sin.c

/// Make CPUs usage as a sin wave

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

const float PI = 3.1415926;
const int TIME_SLICE = 40000;  // 40 ms
const int PIECE = 500;
const int CYCLE = 10;

int get_time_diff(struct timeval *start, struct timeval *end) {
  return 1000000 * (end->tv_sec - start->tv_sec) + end->tv_usec -
         start->tv_usec;
}

void run() {
  pid_t pid = getpid();
  printf("Process ID: %d\n", pid);

  struct timeval start;
  struct timeval end;

  for (int _c = 0; _c < CYCLE; _c++) {  // how many cycles
    for (int i = 0; i < PIECE; i++) {   // a single cycle
      int diff = 0;
      gettimeofday(&start, NULL);

      float ratio = sin(PI * i * 2 / PIECE) * 0.5f + 0.5f;
      int run_time = TIME_SLICE * ratio;

      while (diff < run_time) {
        gettimeofday(&end, NULL);
        diff = get_time_diff(&start, &end);
      }

      usleep(TIME_SLICE - run_time);
    }
  }
}

int main() {
  // create 4 processes for 4 cores
  // each process occupies a core
  fork();  // 2
  fork();  // 4

  run();

  return 0;
}

Result: