A dumb test of how long it takes to send a byte through a pipe, using

timeshared threads and realtime threads.

regress/sys/kern/latency1/Makefile

@@ -0,0 +1,9 @@
+#	$NetBSD: Makefile,v 1.1 2008/05/23 22:22:36 ad Exp $
+
+NOMAN=		# defined
+
+PROG=		latency1
+WARNS?=		4
+LDADD=		-lpthread -lrt
+
+.include <bsd.prog.mk>

regress/sys/kern/latency1/latency1.c

@@ -0,0 +1,143 @@
+/*	$NetBSD: latency1.c,v 1.1 2008/05/23 22:22:36 ad Exp $	*/
+
+/*-
+ * Copyright (c) 2008 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * THIS IS NOT A GOOD TEST OF REALTIME DISPATCH LATENCY AND SHOULD NOT
+ * BE USED AS ONE.
+ *
+ * Two threads are involved in the test.  Every 100ms the first thread
+ * writes a byte down a pipe.  The second thread waits to read it.  The
+ * time taken for the byte to move between threads is measured.  With
+ * no arguments, it uses timeshared threads.  When given any argument
+ * (junk will do) it uses realtime threads.  Ctrl-C ends the test.
+ */
+
+#include <sys/mman.h>
+#include <sys/resource.h>
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sched.h>
+#include <limits.h>
+#include <signal.h>
+#include <err.h>
+
+pthread_barrier_t	barrier;
+struct timespec		start;
+int			fds[2];
+int 			done;
+long			max = 0;
+long			min = LONG_MAX;
+
+static void
+sigint(int junk)
+{
+
+	done = 1;
+}
+
+static void *
+reader(void *cookie)
+{
+	struct timespec end;
+	char buf[1];
+	long val;
+
+	for (;;) {
+		(void)pthread_barrier_wait(&barrier);
+		if (read(fds[0], buf, sizeof(buf)) == -1) {
+			err(1, "read");
+		}
+		clock_gettime(CLOCK_MONOTONIC, &end);
+		timespecsub(&end, &start, &end);
+		val = (long)end.tv_sec * 1000000000 + (long)end.tv_nsec;
+		printf("%ld\n", val);
+		if (val > max)
+			max = val;
+		if (val < min)
+			min = val;
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	static struct timespec delay = { 0, 100000000 };	/* 100ms */
+	struct sched_param sp;
+	pthread_t pt;
+	char buf[1];
+
+	if (geteuid() != 0) {
+		errx(1, "run me as root");
+	}
+	if (pipe(fds)) {
+		err(1, "pipe");
+	}
+	pthread_barrier_init(&barrier, NULL, 2);
+	if (pthread_create(&pt, NULL, reader, NULL)) {
+		errx(1, "pthread_create failed");
+	}
+	if (mlockall(MCL_CURRENT | MCL_FUTURE)) {
+		err(1, "mlockall");
+	}
+	if (signal(SIGINT, sigint)) {
+		err(1, "siginal");
+	}
+	if (argc != 1) {
+		/* Have an argument, use realtime priorities. */
+		sp.sched_priority = sched_get_priority_max(SCHED_FIFO) - 2;
+		if (pthread_setschedparam(pthread_self(), SCHED_FIFO, &sp)) {
+			errx(1, "pthread_setschedparam");
+		}
+		sp.sched_priority = sched_get_priority_max(SCHED_FIFO) - 1;
+		if (pthread_setschedparam(pt, SCHED_FIFO, &sp)) {
+			errx(1, "pthread_setschedparam");
+		}
+	} else {
+		/* Not realtime, set the maximum timeshared priority. */
+		if (setpriority(PRIO_PROCESS, 0, -20)) {
+			err(1, "setpriority");
+		}
+	}
+
+	do {
+		(void)pthread_barrier_wait(&barrier);
+		while (nanosleep(&delay, NULL) != 0) {
+			/* nothing */
+		}
+		clock_gettime(CLOCK_MONOTONIC, &start);
+		if (write(fds[1], buf, sizeof(buf)) == -1) {
+			err(1, "write");
+		}
+	} while (!done);
+
+	printf("\nmin %ldns, max=%ldns\n", min, max);
+	return 0;
+}