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/*
* 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);
}
}
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