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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  *      sched_jitter.c
21  *
22  * DESCRIPTION
23  *      This test measures scheduling jitter w/ realtime processes.
24  *
25  *      It spawns a realtime thread that repeatedly times how long it takes to
26  *      do a fixed amount of work. It then prints out the maximum jitter seen
27  *      (longest execution time - the shortest execution time).
28  *      It also spawns off a realtime thread of higher priority that simply
29  *      wakes up and goes back to sleep. This tries to measure how much overhead
30  *      the scheduler adds in switching quickly to another task and back.
31  *
32  * USAGE:
33  *      Use run_auto.sh script in current directory to build and run test.
34  *
35  * AUTHOR
36  *      John Stultz <johnstul@us.ibm.com>
37  *
38  * HISTORY
39  *      2006-May-05: Initial version by John Stultz <johnstul@us.ibm.com>
40  *      2007-July-18: Support to gather stats by Ankita Garg <ankita@in.ibm.com>
41  *
42  *      This line has to be added to avoid a stupid CVS problem
43  *****************************************************************************/
44 
45 #include <stdio.h>
46 #include <time.h>
47 #include <pthread.h>
48 #include <sched.h>
49 #include <unistd.h>
50 #include <libstats.h>
51 #include <librttest.h>
52 
53 #define NUMRUNS 1000
54 #define NUMLOOPS 1000000
55 #define NSEC_PER_SEC 1000000000
56 #define WORKLEN 64
57 #define ISLEEP 50000
58 
59 int array[WORKLEN];
60 
61 volatile int flag;		/*let interrupter know we're done */
62 
usage(void)63 void usage(void)
64 {
65 	rt_help();
66 	printf("sched_jitter specific options:\n");
67 }
68 
parse_args(int c,char * v)69 int parse_args(int c, char *v)
70 {
71 
72 	int handled = 1;
73 	switch (c) {
74 	case 'h':
75 		usage();
76 		exit(0);
77 	default:
78 		handled = 0;
79 		break;
80 	}
81 	return handled;
82 }
83 
ts_sub(struct timespec a,struct timespec b)84 unsigned long long ts_sub(struct timespec a, struct timespec b)
85 {
86 	unsigned long long first, second;
87 
88 	first = (unsigned long long)a.tv_sec * NSEC_PER_SEC + a.tv_nsec;
89 	second = (unsigned long long)b.tv_sec * NSEC_PER_SEC + b.tv_nsec;
90 	return first - second;
91 }
92 
print_unit(unsigned long long val)93 void print_unit(unsigned long long val)
94 {
95 	if (val > 1000000)
96 		printf("%f ms\n", (float)(val) / 1000000);
97 	else if (val > 1000)
98 		printf("%f us\n", (float)(val) / 1000);
99 	else
100 		printf("%f ns\n", (float)val);
101 
102 }
103 
do_work(int runs)104 void do_work(int runs)
105 {
106 	int i, j;
107 	for (i = 0; i < runs; i++) {
108 		for (j = 0; j < WORKLEN - 1; j++)
109 			array[j] = array[j] + array[j + 1];
110 		for (j = 0; j < WORKLEN - 1; j++)
111 			array[j] = array[j] - array[j + 1];
112 	}
113 }
114 
thread_worker(void * arg)115 void *thread_worker(void *arg)
116 {
117 	struct timespec start, stop;
118 	int i;
119 	unsigned long long delta;
120 	unsigned long long min = -1, max = 0;
121 
122 	stats_container_t dat;
123 	stats_record_t rec;
124 
125 	stats_container_init(&dat, NUMRUNS);
126 
127 	for (i = 0; i < NUMRUNS; i++) {
128 
129 		do_work(1);	/* warm cache */
130 
131 		/* do test */
132 		clock_gettime(CLOCK_MONOTONIC, &start);
133 		do_work(NUMLOOPS);
134 		clock_gettime(CLOCK_MONOTONIC, &stop);
135 
136 		/* calc delta, min and max */
137 		delta = ts_sub(stop, start);
138 		if (delta < min)
139 			min = delta;
140 		if (delta > max)
141 			max = delta;
142 		rec.x = i;
143 		rec.y = delta;
144 		stats_container_append(&dat, rec);
145 
146 		printf("delta: %llu ns\n", delta);
147 		usleep(1);	/* let other things happen */
148 	}
149 
150 	printf("max jitter: ");
151 	print_unit(max - min);
152 	stats_container_save("samples", "Scheduling Jitter Scatter Plot",
153 			     "Iteration", "Delay (ns)", &dat, "points");
154 	return NULL;
155 }
156 
thread_interrupter(void * arg)157 void *thread_interrupter(void *arg)
158 {
159 	while (!flag)
160 		usleep(ISLEEP);
161 	return NULL;
162 }
163 
main(int argc,char * argv[])164 int main(int argc, char *argv[])
165 {
166 	int worker, interrupter;
167 
168 	setup();
169 
170 	rt_init("h", parse_args, argc, argv);
171 
172 	interrupter = create_fifo_thread(thread_interrupter, NULL, 80);
173 	sleep(1);
174 	worker = create_fifo_thread(thread_worker, NULL, 10);
175 
176 	join_thread(worker);
177 	flag = 1;
178 	join_thread(interrupter);
179 
180 	return 0;
181 }
182