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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  *      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 (at) us.ibm.com>
     32  *
     33  * HISTORY
     34  *      2006-Nov-15: Initial version by Darren Hart <dvhltc (at) 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 
     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 
     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 */
     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 */
     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 
     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, &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