added cache_benchmark

cache_benchmark/cache.c

@@ -0,0 +1,107 @@
+#include<stdio.h>
+#include<stdlib.h>
+#include<time.h>
+
+//prints out usage information
+void usage();
+
+//generate dynamically allocated array, initialized with rand()
+int* rand_array(size_t n);
+
+//converts clock ticks to nano seconds
+double clocks_to_ns(double ct);
+
+//write to /dev/null or nul
+//exits if it fails
+void int_to_dev_null(int trash);
+
+//calculates the clock ticks rand() probably needs
+//from a hot cache
+double clock_ticks_rand();
+
+int main(int argc, char* argv[]) {
+	if(argc != 4) {
+		usage();
+		return 1;
+	}	
+	unsigned n_bytes;
+	unsigned array_size;
+	unsigned n_times_access;
+	unsigned n_loops;
+	sscanf(argv[1], "%u", &n_bytes);
+	sscanf(argv[2], "%u", &n_times_access);
+	sscanf(argv[3], "%u", &n_loops);
+	srand(time(NULL));
+	array_size = n_bytes / 4;
+	int* parry = rand_array(array_size);
+
+	clock_t start;
+	clock_t end;
+	clock_t overall = 0;
+	int tmp = 0;
+	double rc = clock_ticks_rand();
+	for(size_t n=0; n<n_loops; ++n) {
+		start = clock();
+		for(size_t t=0; t<n_times_access; ++t) {
+			//alternative way(without inner rand): tmp += parry[parry[t % array_size] % array_size];
+			tmp += parry[rand() % array_size];
+		}
+		end = clock();
+		overall += (end - start);
+	}
+	double per_instruct_ticks = overall / ((double) n_times_access * n_loops);
+	per_instruct_ticks = per_instruct_ticks - rc;
+	printf("%u, %u, %lf, %lf\n", n_bytes, array_size, clocks_to_ns(per_instruct_ticks), clocks_to_ns(rc));
+	int_to_dev_null(tmp);
+}
+double clocks_to_ns(double ct) {
+	return ct / CLOCKS_PER_SEC * 1000000000.0;
+}
+void int_to_dev_null(int trash) {
+#ifdef _WIN32
+	const char* dev_null = "nul";
+#else
+	const char* dev_null = "/dev/null";
+#endif
+	FILE* fnull = fopen(dev_null, "w");
+	if(! fnull) {
+		perror("unable to open /dev/null or nul");
+		exit(2);
+	}
+	fprintf(fnull, "%d", trash);
+	fclose(fnull);
+}
+
+int* array(size_t n) {
+	int* p=NULL;
+        p = malloc(sizeof(int) * n);
+	if(!p) {
+		perror("malloc failed");
+		exit(2);
+	}
+	return p;
+}
+int* rand_array(size_t n) {
+	int* p = array(n);
+	for(size_t i=0; i<n; ++i) {
+		p[i] = rand();
+	}
+	return p;
+}
+
+void usage() {
+	printf("<prog> array-size n-times-access n-loops\n");
+}
+double clock_ticks_rand() {
+#define N 1000000
+	for(size_t i=0; i<N; ++i) {
+		rand();
+	}
+	clock_t start = clock();
+	for(size_t i=0; i<N; ++i) {
+		rand();
+	}
+	double time_per_rand = (double)(clock() - start) / N;
+	return time_per_rand;
+#undef N
+}