postgresql/contrib/pg_test_timing/pg_test_timing.c

/*
 *	pg_test_timing.c
 *		tests overhead of timing calls and their monotonicity:	that
 *		they always move forward
 */

#include "postgres_fe.h"

#include "getopt_long.h"
#include "portability/instr_time.h"

static const char *progname;

static int32 test_duration = 3;

static void handle_args(int argc, char *argv[]);
static uint64 test_timing(int32);
static void output(uint64 loop_count);

/* record duration in powers of 2 microseconds */
int64 histogram[32];

int
main(int argc, char *argv[])
{
	uint64		loop_count;

	progname = get_progname(argv[0]);

	handle_args(argc, argv);

	loop_count = test_timing(test_duration);

	output(loop_count);

	return 0;
}

static void
handle_args(int argc, char *argv[])
{
	static struct option long_options[] = {
		{"duration", required_argument, NULL, 'd'},
		{NULL, 0, NULL, 0}
	};

	int			option;			/* Command line option */
	int			optindex = 0;	/* used by getopt_long */

	if (argc > 1)
	{
		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-h") == 0 ||
			strcmp(argv[1], "-?") == 0)
		{
			printf("Usage: %s [-d DURATION]\n", progname);
			exit(0);
		}
		if (strcmp(argv[1], "--version") == 0 || strcmp(argv[1], "-V") == 0)
		{
			puts("pg_test_timing (PostgreSQL) " PG_VERSION);
			exit(0);
		}
	}

	while ((option = getopt_long(argc, argv, "d:",
								 long_options, &optindex)) != -1)
	{
		switch (option)
		{
			case 'd':
				test_duration = atoi(optarg);
				break;

			default:
				fprintf(stderr, "Try \"%s --help\" for more information.\n",
						progname);
				exit(1);
				break;
		}
	}

	if (argc > optind)
	{
		fprintf(stderr,
				"%s: too many command-line arguments (first is \"%s\")\n",
				progname, argv[optind]);
		fprintf(stderr, "Try \"%s --help\" for more information.\n",
				progname);
		exit(1);
	}

	if (test_duration > 0)
	{
		printf("Testing timing overhead for %d seconds.\n", test_duration);
	}
	else
	{
		fprintf(stderr,
			"%s: duration must be a positive integer (duration is \"%d\")\n",
				progname, test_duration);
		fprintf(stderr, "Try \"%s --help\" for more information.\n",
				progname);
		exit(1);
	}
}

static uint64
test_timing(int32 duration)
{
	uint64		total_time;
	int64		time_elapsed = 0;
	uint64		loop_count = 0;
	uint64		prev, cur;
	instr_time	start_time, end_time, temp;

	total_time = duration > 0 ? duration * 1000000 : 0;

	INSTR_TIME_SET_CURRENT(start_time);
	cur = INSTR_TIME_GET_MICROSEC(start_time);

	while (time_elapsed < total_time)
	{
		int32		diff, bits = 0;

		prev = cur;
		INSTR_TIME_SET_CURRENT(temp);
		cur = INSTR_TIME_GET_MICROSEC(temp);
		diff = cur - prev;

		/* Did time go backwards? */
		if (diff < 0)
		{
			printf("Detected clock going backwards in time.\n");
			printf("Time warp: %d microseconds\n", diff);
			exit(1);
		}

		/* What is the highest bit in the time diff? */
		while (diff)
		{
			diff >>= 1;
			bits++;
		}

		/* Update appropriate duration bucket */
		histogram[bits]++;

		loop_count++;
		INSTR_TIME_SUBTRACT(temp, start_time);
		time_elapsed = INSTR_TIME_GET_MICROSEC(temp);
	}

	INSTR_TIME_SET_CURRENT(end_time);

	INSTR_TIME_SUBTRACT(end_time, start_time);

	printf("Per loop time including overhead: %0.2f nsec\n",
		   INSTR_TIME_GET_DOUBLE(end_time) * 1e9 / loop_count);

	return loop_count;
}

static void
output(uint64 loop_count)
{
	int64		max_bit = 31, i;

	/* find highest bit value */
	while (max_bit > 0 && histogram[max_bit] == 0)
		max_bit--;
		
	printf("Histogram of timing durations:\n");
	printf("%6s   %10s %10s\n", "< usec", "% of total", "count");

	for (i = 0; i <= max_bit; i++)
	{
		char		buf[100];

		/* lame hack to work around INT64_FORMAT deficiencies */
		snprintf(buf, sizeof(buf), INT64_FORMAT, histogram[i]);
		printf("%6ld    %9.5f %10s\n", 1l << i,
				(double) histogram[i] * 100 / loop_count, buf);
	}
}