1 /******************************************************************************
2 *
3 * Copyright © International Business Machines Corp., 2006, 2008
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
13 * the GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
18 *
19 * NAME
20 * rdtsc-latency.c
21 *
22 * DESCRIPTION
23 * Simple program to measure the time between several pairs of calls to
24 * rdtsc(). Based off of gtod-latency.c
25 *
26 * USAGE:
27 * Use run_auto.sh script in current directory to build and run test.
28 * Use "-j" to enable jvm simulator.
29 *
30 * AUTHOR
31 * Darren Hart <dvhltc@us.ibm.com>
32 *
33 * HISTORY
34 * 2006-Nov-15: Initial version by Darren Hart <dvhltc@us.ibm.com>
35 *
36 *****************************************************************************/
37
38 #include <stdio.h>
39 #include <stdlib.h>
40 #include <unistd.h>
41 #include <sys/time.h>
42 #include <sys/types.h>
43 #include <sched.h>
44 #include <errno.h>
45 #include <stdint.h>
46 #include <librttest.h>
47 #include <libtsc.h>
48
49 #define ITERATIONS 1000000
50
usage(void)51 void usage(void)
52 {
53 rt_help();
54 printf("rdtsc-latency specific options:\n");
55 printf(" This testcase don't expect any commandline options\n");
56 }
57
parse_args(int c,char * v)58 int parse_args(int c, char *v)
59 {
60
61 int handled = 1;
62 switch (c) {
63 case 'h':
64 usage();
65 exit(0);
66 default:
67 handled = 0;
68 break;
69 }
70 return handled;
71 }
72
73 /* return difference in nanoseconds */
tv_minus(struct timeval * tv_start,struct timeval * tv_end)74 unsigned long long tv_minus(struct timeval *tv_start, struct timeval *tv_end)
75 {
76 unsigned long long nsecs;
77 nsecs = (tv_end->tv_sec - tv_start->tv_sec) * 1000000000ULL;
78 nsecs += (tv_end->tv_usec - tv_start->tv_usec) * 1000;
79 return nsecs;
80 }
81
82 /* calculate the tsc period */
tsc_period_ps(void)83 unsigned long long tsc_period_ps(void)
84 {
85 struct timeval tv_start;
86 struct timeval tv_end;
87 unsigned long long tsc_start, tsc_end;
88
89 rdtscll(tsc_start);
90 gettimeofday(&tv_start, NULL);
91 sleep(1);
92 rdtscll(tsc_end);
93 gettimeofday(&tv_end, NULL);
94
95 return (1000 * tv_minus(&tv_start, &tv_end)) / tsc_minus(tsc_start,
96 tsc_end);
97 }
98
main(int argc,char * argv[])99 int main(int argc, char *argv[])
100 {
101 int i, err;
102 unsigned long long deltas[ITERATIONS];
103 unsigned long long max, min, avg, tsc_a, tsc_b, tsc_period;
104 struct sched_param param;
105
106 #ifdef TSC_UNSUPPORTED
107 printf("Error: test cannot be executed on an arch wihout TSC.\n");
108 return ENOTSUP;
109 #endif
110
111 setup();
112
113 rt_init("h", parse_args, argc, argv);
114
115 /* no arguments */
116 if (argc > 1) {
117 fprintf(stderr, "%s accepts no arguments\n", argv[0]);
118 exit(1);
119 }
120
121 /* switch to SCHED_FIFO 99 */
122 param.sched_priority = sched_get_priority_max(SCHED_FIFO);
123 err = sched_setscheduler(0, SCHED_FIFO, ¶m);
124
125 /* Check that the user has the appropriate privileges */
126 if (err) {
127 if (errno == EPERM) {
128 fprintf(stderr,
129 "This program runs with a scheduling policy of SCHED_FIFO at priority %d\n",
130 param.sched_priority);
131 fprintf(stderr,
132 "You don't have the necessary privileges to create such a real-time process.\n");
133 } else {
134 fprintf(stderr, "Failed to set scheduler, errno %d\n",
135 errno);
136 }
137 exit(1);
138 }
139
140 /* calculate the tsc period in picoseconds */
141 tsc_period = tsc_period_ps();
142
143 /* collect ITERATIONS pairs of gtod calls */
144 max = min = avg = 0;
145 for (i = 0; i < ITERATIONS; i++) {
146 rdtscll(tsc_a);
147 rdtscll(tsc_b);
148 deltas[i] = (tsc_minus(tsc_a, tsc_b) * tsc_period) / 1000; /* tsc period is in ps */
149 if (i == 0 || deltas[i] < min)
150 min = deltas[i];
151 if (deltas[i] > max)
152 max = deltas[i];
153 avg += deltas[i];
154 }
155 avg /= ITERATIONS;
156
157 /* report on deltas */
158 printf("Calculated tsc period = %llu ps\n", tsc_period);
159 printf("%d pairs of rdtsc() calls completed\n", ITERATIONS);
160 printf("Time between calls:\n");
161 printf(" Max: %llu ns\n", max);
162 printf(" Min: %llu ns\n", min);
163 printf(" Avg: %llu ns\n", avg);
164
165 return 0;
166 }
167