add system call overhead measurement program

Run this tool (and a background workload) to measure system call
overheads.

1 files changed, 62 insertions, 0 deletions

diff --git a/bin/null_call.c b/bin/null_call.c
new file mode 100644
index 0000000..94ba866
--- /dev/null
+++ b/bin/null_call.c
@@ -0,0 +1,62 @@
+#include <sys/time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <math.h>
+
+#include "litmus.h"
+#include "cycles.h"
+
+static void time_null_call(void)
+{
+        cycles_t t0, t1, t2;
+        int ret;
+
+        t0 = get_cycles();
+        ret = null_call(&t1);
+        t2 = get_cycles();
+        if (ret != 0)
+                perror("null_call");
+        printf("%10" CYCLES_FMT ", " 
+               "%10" CYCLES_FMT ", "
+               "%10" CYCLES_FMT ", "
+               "%10" CYCLES_FMT ", "
+               "%10" CYCLES_FMT ", "
+               "%10" CYCLES_FMT "\n",
+               t0, t1, t2, t1 - t0, t2 - t1, t2 - t0);
+}
+
+static struct timespec sec2timespec(double seconds)
+{
+        struct timespec tspec;
+        double full_secs = floor(seconds);
+        tspec.tv_sec  = (time_t) full_secs;
+        tspec.tv_nsec = (long) ((seconds  - full_secs) * 1000000000L);
+        return tspec;
+}
+
+int main(int argc, char **argv)
+{
+        double delay;
+        struct timespec sleep_time;
+        
+        if (argc == 2) {
+                delay = atof(argv[1]);
+                sleep_time = sec2timespec(delay);
+                if (delay <= 0.0)
+                        fprintf(stderr, "Invalid time spec: %s\n", argv[1]);
+                fprintf(stderr, "Measuring syscall overhead every "
+                        "%lus and %luns.\n",
+                        (unsigned long) sleep_time.tv_sec,
+                        (unsigned long) sleep_time.tv_nsec);
+                do {
+                        time_null_call();
+                } while (nanosleep(&sleep_time, NULL) == 0);
+        } else {
+                fprintf(stderr, "Press enter key to measure...\n");
+                while (getchar() != EOF) {
+                        time_null_call();
+                }
+        }
+        return 0;
+}