1 /* $NetBSD: latency1.c,v 1.1 2008/05/23 22:22:36 ad Exp $ */
2
3 /*-
4 * Copyright (c) 2008 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
19 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 /*
30 * THIS IS NOT A GOOD TEST OF REALTIME DISPATCH LATENCY AND SHOULD NOT
31 * BE USED AS ONE.
32 *
33 * Two threads are involved in the test. Every 100ms the first thread
34 * writes a byte down a pipe. The second thread waits to read it. The
35 * time taken for the byte to move between threads is measured. With
36 * no arguments, it uses timeshared threads. When given any argument
37 * (junk will do) it uses realtime threads. Ctrl-C ends the test.
38 */
39
40 #include <sys/mman.h>
41 #include <sys/resource.h>
42
43 #include <pthread.h>
44 #include <stdio.h>
45 #include <stdlib.h>
46 #include <unistd.h>
47 #include <sched.h>
48 #include <limits.h>
49 #include <signal.h>
50 #include <err.h>
51
52 pthread_barrier_t barrier;
53 struct timespec start;
54 int fds[2];
55 int done;
56 long max = 0;
57 long min = LONG_MAX;
58
59 static void
sigint(int junk)60 sigint(int junk)
61 {
62
63 done = 1;
64 }
65
66 static void *
reader(void * cookie)67 reader(void *cookie)
68 {
69 struct timespec end;
70 char buf[1];
71 long val;
72
73 for (;;) {
74 (void)pthread_barrier_wait(&barrier);
75 if (read(fds[0], buf, sizeof(buf)) == -1) {
76 err(1, "read");
77 }
78 clock_gettime(CLOCK_MONOTONIC, &end);
79 timespecsub(&end, &start, &end);
80 val = (long)end.tv_sec * 1000000000 + (long)end.tv_nsec;
81 printf("%ld\n", val);
82 if (val > max)
83 max = val;
84 if (val < min)
85 min = val;
86 }
87 }
88
89 int
main(int argc,char * argv[])90 main(int argc, char *argv[])
91 {
92 static struct timespec delay = { 0, 100000000 }; /* 100ms */
93 struct sched_param sp;
94 pthread_t pt;
95 char buf[1];
96
97 if (geteuid() != 0) {
98 errx(1, "run me as root");
99 }
100 if (pipe(fds)) {
101 err(1, "pipe");
102 }
103 pthread_barrier_init(&barrier, NULL, 2);
104 if (pthread_create(&pt, NULL, reader, NULL)) {
105 errx(1, "pthread_create failed");
106 }
107 if (mlockall(MCL_CURRENT | MCL_FUTURE)) {
108 err(1, "mlockall");
109 }
110 if (signal(SIGINT, sigint)) {
111 err(1, "siginal");
112 }
113 if (argc != 1) {
114 /* Have an argument, use realtime priorities. */
115 sp.sched_priority = sched_get_priority_max(SCHED_FIFO) - 2;
116 if (pthread_setschedparam(pthread_self(), SCHED_FIFO, &sp)) {
117 errx(1, "pthread_setschedparam");
118 }
119 sp.sched_priority = sched_get_priority_max(SCHED_FIFO) - 1;
120 if (pthread_setschedparam(pt, SCHED_FIFO, &sp)) {
121 errx(1, "pthread_setschedparam");
122 }
123 } else {
124 /* Not realtime, set the maximum timeshared priority. */
125 if (setpriority(PRIO_PROCESS, 0, -20)) {
126 err(1, "setpriority");
127 }
128 }
129
130 do {
131 (void)pthread_barrier_wait(&barrier);
132 while (nanosleep(&delay, NULL) != 0) {
133 /* nothing */
134 }
135 clock_gettime(CLOCK_MONOTONIC, &start);
136 if (write(fds[1], buf, sizeof(buf)) == -1) {
137 err(1, "write");
138 }
139 } while (!done);
140
141 printf("\nmin %ldns, max=%ldns\n", min, max);
142 return 0;
143 }
144