Add limit.c: get the highest rate possible

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 81 insertions, 0 deletions

diff --git a/limit.c b/limit.c
new file mode 100644
index 0000000..7aea33f
--- /dev/null
+++ b/limit.c
@@ -0,0 +1,81 @@
+/* See LICENSE file for copyright and license details. */
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+
+
+#ifndef CAPACITY
+# define CAPACITY (1 << 20)
+#endif
+
+
+int
+main(int argc, char *argv[])
+{
+	static char buf[1 << 16];
+	int rw1[2], rw2[2], n = 0, m;
+	ssize_t r, p, w;
+	size_t sum = 0, totsum = 0;
+	struct timespec start, end;
+	double rate;
+
+	if (!argc)
+		*argv = "limit";
+
+	if (pipe(rw1) || fcntl(*rw1, F_SETPIPE_SZ, CAPACITY) != CAPACITY)
+		goto fail;
+	if (pipe(rw2) || fcntl(*rw2, F_SETPIPE_SZ, CAPACITY) != CAPACITY)
+		goto fail;
+
+	for (n = CAPACITY; n; n -= (int)r)
+		if ((r = write(rw1[1], buf, n)) < 0)
+			goto fail;
+
+	if (clock_gettime(CLOCK_MONOTONIC, &start))
+		goto fail;
+	for (;;) {
+		r = splice(rw1[0], NULL, rw2[1], NULL, CAPACITY, 0);
+		if (r <= 0) {
+			if (r < 0)
+				goto fail;
+			goto done;
+		}
+		for (p = 0; p < r; p += w) {
+			w = splice(rw2[0], NULL, rw1[1], NULL, r - p, 0);
+			if (w <= 0) {
+				if (w < 0)
+					goto fail;
+				goto done;
+			}
+		}
+		sum += (size_t)r << 1;
+		if (++n == 100000) {
+			if (clock_gettime(CLOCK_MONOTONIC, &end))
+				goto fail;
+			n = 0;
+			start.tv_sec  = end.tv_sec  - start.tv_sec;
+			start.tv_nsec = end.tv_nsec - start.tv_nsec;
+			rate = (double)start.tv_nsec;
+			rate /= 1000000000.;
+			rate += start.tv_sec;
+			rate = (double)sum / rate;
+			rate /= 1000000000.;
+			totsum += sum;
+			sum = 0;
+			dprintf(STDERR_FILENO, "  %lf GB/s\033[K\n\033[A", rate);
+			start = end;
+		}
+	}
+
+done:
+	return 0;
+
+fail:
+	perror(*argv);
+	return 1;
+}