/*
 * Utility to estimate the overhead of timecounter hardware.
 *
 * cc tc.c
 * sudo ./a.out HPET; sudo ./a.out TSC; sudo ./a.out ACPI-fast
 */
#include <sys/time.h>
#include <sys/sysctl.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <libgen.h>

static const char *progname;

static void
usage(int rc)
{

	fprintf(stderr, "%s: [-h][-i <iterations>] [-s <usecs>] <tc_choice>\n",
	    progname);
	exit(rc);
}

int
main(int argc, char *argv[])
{
	int ch, error;
        long delta, iterations, i, usecs;
	char *tc_choice;
        struct timespec ts1, ts2, ts;
	sbintime_t sbt1, sbt2;

	progname = basename(argv[0]);
	iterations = 1000000;
	usecs = 0;

	while ((ch = getopt(argc, argv, "i:s:")) != -1) {
		switch (ch) {
		case 'i':
			iterations = strtol(optarg, NULL, 0);
			break;
		case 's':
			usecs = strtol(optarg, NULL, 0);
			break;
		case 'h':
			usage(0);
		default:
			usage(1);
		}
	}

	argc -= optind;
	argv += optind;

	if (argc != 1)
		usage(1);

	tc_choice = argv[0];
	error = sysctlbyname("kern.timecounter.hardware", NULL, NULL,
	    tc_choice, strlen(tc_choice) + 1);
	if (error) {
		fprintf(stderr, "Error changing timecounter to \"%s\"\n",
		    tc_choice);
		fprintf(stderr, "sysctl node kern.timecounter.choice lists "
		    "valid timecounter names\n");
		exit(1);
	}
	usleep(usecs);

	clock_gettime(CLOCK_UPTIME_PRECISE, &ts1);

        for (i = 0; i < iterations; i++)
                (void)clock_gettime(CLOCK_MONOTONIC_PRECISE, &ts);

	clock_gettime(CLOCK_UPTIME_PRECISE, &ts2);

	sbt1 = tstosbt(ts1);
	sbt2 = tstosbt(ts2);
	ts = sbttots(sbt2 - sbt1);
	delta = ts.tv_sec * 1000000000 + ts.tv_nsec;

	printf("%s: ts1 (%ld.%ld) ts2 (%ld.%ld) delta (%ld msecs)\n",
	    tc_choice, ts1.tv_sec, ts1.tv_nsec, ts2.tv_sec, ts2.tv_nsec,
	    delta / 1000000);
}