From 77fb4c791241998a85496388337a2d4c80e512c7 Mon Sep 17 00:00:00 2001
From: "B. Watson" <yalhcru@gmail.com>
Date: Thu, 22 Jul 2021 16:50:09 -0400
Subject: Add -b (benchmark) flag

---
 slowbaud.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 11 deletions(-)

(limited to 'slowbaud.c')

diff --git a/slowbaud.c b/slowbaud.c
index bbf31ac..63a8a3b 100644
--- a/slowbaud.c
+++ b/slowbaud.c
@@ -26,7 +26,7 @@
 	#include <pty.h>
 #endif
 
-#define DEFAULT_BPS 1200
+#define DEFAULT_BPS 2400
 #define MIN_BPS 1
 #define MAX_BPS 500000
 
@@ -67,6 +67,8 @@ void setup_timer(void) {
 	sigprocmask(SIG_BLOCK, &sigmask, NULL);
 }
 
+/* on both Linux and OSX, using setitimer() and sigwait() gives better
+   timing accuracy than usleep() or nanosleep(). */
 void slow_write(int outfd, char c) {
 	int j;
 	unsigned long now, target, overslept;
@@ -84,13 +86,8 @@ void slow_write(int outfd, char c) {
 	if(now > target) {
 		overslept = now - target;
 		if(overslept < interval) {
-			unsigned long old = itv.it_interval.tv_usec;
 			itv.it_interval.tv_usec -= overslept;
 			itv.it_value.tv_usec = itv.it_interval.tv_usec;
-			if(debug) {
-				fprintf(stderr, "tv_usec was %ldms, overslept %ld, new tv_usec %ldms\n",
-						old, overslept, itv.it_interval.tv_usec);
-			}
 		}
 	} else {
 		while(NOW_USEC() < target)
@@ -99,24 +96,25 @@ void slow_write(int outfd, char c) {
 }
 
 void debug_stats(void) {
-	if(outbytes && debug) {
+	if(outbytes) {
 		unsigned long elapsed_us = NOW_USEC() - starttime;
 		double elapsed_sec = ((double)elapsed_us/1000000.0L);
 		double finterval = (1000000.0L / ((double)bps / 10.0L));
 		double actual = ((double)outbytes * 10.0L) / elapsed_sec;
 		double offby = 100.0L * (((double)bps / actual) - 1.0L);
 		fprintf(stderr,
-				"outbytes %lu, elapsed_us %lu, requested bps %d (%.2fms), "
+				"outbytes %lu, elapsed_us %lu, tv_usec %lu, requested bps %d (%.2fms), "
 				"actual %.2f, accuracy %.2f%%\n",
-				outbytes, elapsed_us, bps, finterval, actual, 100.0 - offby);
+				outbytes, elapsed_us, itv.it_value.tv_usec, bps, finterval, actual, 100.0 - offby);
 	}
-	outbytes = 0;
 }
 
 void slowcat(int infd) {
 	int c;
 
+	outbytes = 0;
 	starttime = NOW_USEC();
+
 	while(read(infd, &c, 1) == 1) {
 		slow_write(1, c);
 	}
@@ -216,12 +214,32 @@ void echo_args(char **args) {
 	exit(0);
 }
 
+void benchmark(char **args) {
+	int bytes = 0, devnull;
+
+	if(*args) bytes = atoi(*args);
+	if(bytes < 1) bytes = 4096;
+	fprintf(stderr, "benchmarking with %d bytes\n", bytes);
+
+	devnull = open("/dev/null", O_RDONLY);
+	if(devnull < 1) die("/dev/null");
+
+	starttime = NOW_USEC();
+	while(bytes--)
+		slow_write(devnull, 0);
+	close(devnull);
+
+	debug_stats();
+	exit(0);
+}
+
 void usage(int exitstat) {
 	printf("Usage: %s [<bits-per-sec>] [<file> [<file> ...]]\n", self);
 	printf("       With no filenames, reads stdin.\n");
 	printf("or:    %s [<bits-per-sec>] -c [<command> [<arg> ...]]\n", self);
 	printf("       With no command, spawns a shell.\n");
 	printf("or:    %s [<bits-per-sec>] -e <string> [<string> ...]\n", self);
+	printf("or:    %s [<bits-per-sec>] -b [<bytes>]\n", self);
 	printf("With no <bits-per-sec>, default rate is %d\n", DEFAULT_BPS);
 	exit(exitstat);
 }
@@ -232,6 +250,7 @@ int main(int argc, char **argv) {
 
 	if(getenv("SLOWBAUD_DEBUG")) debug = 1;
 
+	/* for usage message, we want "slowbaud", not "/path/to/slowbaud" */
 	self = argv[0];
 	for(p = argv[0]; *p; p++) {
 		if(*p == '/') self = p + 1;
@@ -259,7 +278,12 @@ int main(int argc, char **argv) {
 	}
 
 	/* if we used only integer math here, we couldn't support bps not
-      a multiple of 10 (e.g. 75 would be taken as 70). */
+      a multiple of 10 (e.g. 75 would be taken as 70).
+      We still have a rounding problem: 115200bps is 86.81ms/char, but
+      it gets rounded down to 86 here. Which would be around 116279bps,
+      or almost 1% too fast. We never reach 100% speed anyway, so the
+      loss from overhead actually offsets the extra bit of speed.
+	 */
 	interval = (unsigned long)(1000000.0L / ((double)bps / 10.0L));
 	if(debug) fprintf(stderr, "interval %ld us\n", interval);
 
@@ -284,6 +308,9 @@ int main(int argc, char **argv) {
 				if(debug) fprintf(stderr, "-e given, echoing args\n");
 				echo_args(++argv);
 				break;
+			case 'b':
+				benchmark(++argv);
+				break;
 			case 'h':
 			case '?':
 				usage(0);
-- 
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