1 files changed, 99 insertions, 0 deletions
diff --git a/perf_event_open.c b/perf_event_open.c
new file mode 100644
index 0000000..fb44469
--- /dev/null
+++ b/perf_event_open.c
@@ -0,0 +1,99 @@
+/* Copyright (c) 2015, Linaro Limited
+ * All rights reserved.
+ *
+ * SPDX-License-Identifier:	BSD-3-Clause
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/syscall.h>
+#include <linux/perf_event.h>
+
+static int fddev = -1;
+__attribute__((constructor)) static void
+init(void)
+{
+	static struct perf_event_attr attr;
+	attr.type = PERF_TYPE_HARDWARE;
+	attr.config = PERF_COUNT_HW_CPU_CYCLES;
+	fddev = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
+}
+
+__attribute__((destructor)) static void
+fini(void)
+{
+	close(fddev);
+}
+
+	static inline long long
+cpucycles(void)
+{
+	long long result = 0;
+	if (read(fddev, &result, sizeof(result)) < sizeof(result))
+		return 0;
+	return result;
+}
+
+/* Simple loop body to keep things interested. Make sure it gets inlined. */
+	static inline int
+loop(int* __restrict__ a, int* __restrict__ b, int n)
+{
+	unsigned sum = 0;
+	int i = 0;
+	for (i = 0; i < n; ++i)
+		if (a[i] > b[i])
+			sum += a[i] + 5;
+	return sum;
+}
+
+	int
+main(int ac, char **av)
+{
+	long long time_start = 0;
+	long long time_end   = 0;
+
+	int *a  = NULL;
+	int *b  = NULL;
+	int len = 0;
+	int i, sum = 0;
+	if (ac != 2)
+		return -1;
+	len = atoi(av[1]);
+	printf("%s: len = %d\n", av[0], len);
+
+	a = malloc(len*sizeof(*a));
+	b = malloc(len*sizeof(*b));
+
+	for (i = 0; i < len; ++i) {
+		a[i] = i+128;
+		b[i] = i+64;
+	}
+	printf("%s: beginning loop\n", av[0]);
+	time_start = time_end = 0;
+	/* --------------------Critical section-------------- */
+	time_start = cpucycles();
+	for (i = 0; i < 1000; i++) {
+		sum = loop(a, b, len);
+		cpucycles();
+	}
+	time_end = cpucycles();
+	/* ---------------------------------- */
+	printf("sum = %d; Avg time delta[Loop + Read] = %llu\n", sum,
+	       (time_end - time_start)/1000);
+	time_start = time_end = 0;
+	/* --------------------Critical section-------------- */
+	time_start = cpucycles();
+	for (i = 0; i < 1000; i++)
+		sum = loop(a, b, len);
+	time_end = cpucycles();
+	/* ---------------------------------- */
+	printf("sum = %d; Avg time delta[Loop]\t = %llu\n", sum,
+	       (time_end - time_start)/1000);
+	free(a);
+	free(b);
+	return 0;
+}