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
51void 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
58int 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 */
74unsigned 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 */
83unsigned 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
99int 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, &param);
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