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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 (at) us.ibm.com>
     37  *
     38  * HISTORY
     39  *      2006-May-05: Initial version by John Stultz <johnstul (at) us.ibm.com>
     40  *      2007-July-18: Support to gather stats by Ankita Garg <ankita (at) 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 
     63 void usage(void)
     64 {
     65 	rt_help();
     66 	printf("sched_jitter specific options:\n");
     67 }
     68 
     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 
     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 
     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 
    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 
    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 
    157 void *thread_interrupter(void *arg)
    158 {
    159 	while (!flag)
    160 		usleep(ISLEEP);
    161 	return NULL;
    162 }
    163 
    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