cpu hog

2 files changed, 109 insertions, 0 deletions

diff --git a/launch.sh b/launch.sh
new file mode 100755
index 0000000..bb68274
--- /dev/null
+++ b/launch.sh
@@ -0,0 +1,12 @@
+#!/bin/bash
+
+./loop 0 0.33 &
+./loop 1 0.5 &
+./loop 2 0.1 &
+./loop 3 0.2 &
+
+read
+
+kill `pidof loop`
+
+wait
diff --git a/loop.c b/loop.c
new file mode 100644
index 0000000..d18b191
--- /dev/null
+++ b/loop.c
@@ -0,0 +1,97 @@
+#define _GNU_SOURCE /* for cpu sets */
+
+#include <sys/time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <time.h>
+
+#include <sched.h>
+
+static int migrate_to(int target_cpu)
+{
+        cpu_set_t cpu_set;
+
+        CPU_ZERO(&cpu_set);
+        CPU_SET(target_cpu, &cpu_set);
+        return sched_setaffinity(0, sizeof(cpu_set_t), &cpu_set);
+}
+
+static int become_fifo_task(void)
+{
+        struct sched_param sp;
+        sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
+        return sched_setscheduler(0, SCHED_FIFO, &sp);
+}
+
+static int suspend(double seconds)
+{
+        struct timespec delay;
+        delay.tv_sec = (time_t) seconds;
+        delay.tv_nsec = (long) ((seconds - delay.tv_sec) * 1E9);
+        return nanosleep(&delay, NULL);
+}
+
+static double cputime(void)
+{
+        struct timespec ts;
+        int err;
+        err = clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts);
+        if (err != 0)
+                perror("clock_gettime");
+        return (ts.tv_sec + 1E-9 * ts.tv_nsec);
+}
+
+static double wctime(void)
+{
+        struct timeval tv;
+        gettimeofday(&tv, NULL);
+        return (tv.tv_sec + 1E-6 * tv.tv_usec);
+}
+
+static void waste_time(double seconds)
+{
+        double start = cputime();
+
+        while (start + seconds > cputime())
+                ;
+}
+
+
+int main(int argc, char** argv)
+{
+        int i = 1, cpu;
+        double start, end;
+        double delay;
+
+        if (argc != 3) {
+                fprintf(stderr, "usage: loop <cpu> <loop length (seconds)>\n");
+                return 1;
+        } else {
+                cpu   = atoi(argv[1]);
+                delay = atof(argv[2]);
+        }
+
+        if (migrate_to(cpu) != 0) {
+                perror("migrate_to");
+                return 1;
+        }
+
+        if (delay <= 0) {
+                fprintf(stderr, "bad delay: must exceed 0 seconds\n");
+                return 1;
+        }
+
+        if (become_fifo_task() != 0)
+                fprintf(stderr, "cold not become SCHED_FIFO task (%m)\n");
+
+        while (1) {
+                start = wctime();
+                waste_time(delay);
+                end   = wctime();
+                printf("%d: loop %d took %.2f seconds \n",
+                       getpid(), i++, end - start);
+                suspend(delay * 4); /* about 20% utilization */
+        }
+        return 0;
+}