make experiment size adjustable

bench.c

@@ -12,8 +12,8 @@
 void init(int fd);
 void do_write(int fd, const void *buf, size_t count);
 
-const size_t warmup = 10000;
-const size_t iterations = 1000000;
+size_t warmup = 10000;
+size_t iterations = 1000000;
 
 #define BUFSIZE 64
 
@@ -44,10 +44,14 @@ int main() {
 	int fd = create_eventfd();
 
 	init(fd);
+	const size_t exp_warmup = warmup;
+	const size_t exp_iterations = iterations;
 
-	for (size_t i = 0; i < warmup; ++i) do_write(fd, &write_buf, sizeof(write_buf));
+	if (exp_iterations == 0) errx(EXIT_FAILURE, "experiment must do at least one iteration");
 
-	for (int64_t i = 1; i <= iterations; ++i) {
+	for (size_t i = 0; i < exp_warmup; ++i) do_write(fd, &write_buf, sizeof(write_buf));
+
+	for (int64_t i = 1; i <= exp_iterations; ++i) {
 		do_write(fd, &write_buf, sizeof(write_buf));
 		if (__builtin_add_overflow(nanos_sum, clock_diff_nanos(), &nanos_sum))
 			errx(EXIT_FAILURE, "nanos overflowed at %ld", i);
@@ -58,8 +62,8 @@ int main() {
 	// Since uint64_t <-> double conversion are not well defined
 	// and we use really small units (cycles and nanoseconds) I am willing
 	// to accept that we throw away anything after the decimal point.
-	uint64_t avg_nanos = nanos_sum / iterations;
-	uint64_t avg_cycles = cycles_sum / iterations;
+	uint64_t avg_nanos = nanos_sum / exp_iterations;
+	uint64_t avg_cycles = cycles_sum / exp_iterations;
 
 	printf("%lu ns, %lu cycles\n", avg_nanos, avg_cycles);
 	return 0;

common.h

 #pragma once
 
 #define unlikely(x) __builtin_expect(!!(x), 0)
+
+extern size_t warmup, iterations;

paio-thrd.c

@@ -5,6 +5,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#include "common.h"
 #include "stopwatch.h"
 
 atomic_int done;
@@ -19,6 +20,9 @@ void callback(union sigval sigval) {
 }
 
 void init(int fd) {
+	// decrease the experiment size because this takes much longer than anything else
+	warmup = 10;
+	iterations = 100;
 	aiocb.aio_fildes = fd;
 	aiocb.aio_sigevent.sigev_notify = SIGEV_THREAD;
 	aiocb.aio_sigevent.sigev_notify_function = callback;