raidzero · June 10, 2017 17:29 · Jun 10, 2017
diff --git a/Cpu usage over the last second b/Cpu usage over the last second
@@ -0,0 +1,97 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+
+#define BUF_SIZE 4096
+
+typedef struct {
+  unsigned long int user;
+  unsigned long int nice;
+  unsigned long int system;
+  unsigned long int idle;
+  unsigned long int iowait;
+  unsigned long int irq;
+  unsigned long int softirq;
+  unsigned long int steal;
+} cpu_usage;
+
+cpu_usage readStats() {
+  FILE* fp = fopen("/proc/stat", "r");
+
+  cpu_usage usage;
+
+  if (fp != NULL) {
+    char buf[BUF_SIZE];
+
+    while (fgets(buf, BUF_SIZE, fp)) {
+      if (sscanf(buf, "cpu %lu %lu %lu %lu %lu %lu %lu %lu", 
+        &usage.user, &usage.nice, &usage.system, &usage.idle, &usage.iowait, &usage.irq, &usage.softirq, &usage.steal)) {
+        break;
+      }
+    }
+  }
+
+  fclose(fp);
+
+  //printf("usage: %lu %lu %lu %lu %lu %lu %lu %lu\n", 
+  //  usage.user, usage.nice, usage.system, usage.idle, usage.iowait, usage.irq, usage.softirq, usage.steal);
+
+  return usage;
+}
+
+// count from composite value until we reach the intr line
+int countCores() {
+  FILE* fp = fopen("/proc/stat" ,"r");
+    int num = -1;
+  if (fp != NULL) {
+    char buf[BUF_SIZE];
+
+    while (fgets(buf, BUF_SIZE, fp)) {
+      // dont care about composite value
+      if (strstr(buf, "cpu ") != NULL) {
+        continue;
+      }
+      num += 1;
+
+      if (strstr(buf, "intr") != NULL) {
+        fclose(fp);
+        return num;
+      }
+    }
+  }
+
+  return num;
+}
+
+double calculateUsage(cpu_usage u1, cpu_usage u2, int numCores) {
+  unsigned long int totalUsage1 = u1.user + u1.nice + u1.system + u1.irq + u1.softirq + u1.steal;
+  unsigned long int totalUsage2 = u2.user + u2.nice + u2.system + u2.irq + u2.softirq + u2.steal;
+
+  unsigned long int totalIdle1 = u1.idle + u1.iowait;
+  unsigned long int totalIdle2 = u2.idle + u2.iowait;
+
+  unsigned long int total1 = totalUsage1 + totalIdle1;
+  unsigned long int total2 = totalUsage2 + totalIdle2;
+
+  unsigned long int totald = total2 - total1;
+  unsigned long int idled = totalIdle2 - totalIdle1;
+
+  double result = (double) (totald - idled) / (double) totald;
+
+  return result;
+}
+
+int main(void) {
+  int numCores = countCores();
+  // take a reading
+  cpu_usage usage1 = readStats();
+
+  // wait a second and take another
+  sleep(1);
+  cpu_usage usage2 = readStats();
+
+  double usagePercent = calculateUsage(usage1, usage2, numCores) * 100;
+
+  //printf("Usage: %.0f%%\n", usagePercent);
+  printf("%0.2f%%\n", usagePercent);
+}