pg_test_timing.c

Go to the documentation of this file.

/*
 *  pg_test_timing.c
 *      tests overhead of timing calls and their monotonicity:  that
 *      they always move forward
 */
 
#include "postgres_fe.h"
 
#include <limits.h>
 
#include "getopt_long.h"
#include "port/pg_bitutils.h"
#include "portability/instr_time.h"
 
static const char *progname;
 
static unsigned int test_duration = 3;
static double max_rprct = 99.99;
 
/* record duration in powers of 2 nanoseconds */
static long long int histogram[64];
 
/* record counts of first 10K durations directly */
#define NUM_DIRECT 10000
static long long int direct_histogram[NUM_DIRECT];
 
/* separately record highest observed duration */
static int64 largest_diff;
static long long int largest_diff_count;
 
 
static void handle_args(int argc, char *argv[]);
static void test_system_timing(void);
#if PG_INSTR_TSC_CLOCK
static void test_tsc_timing(void);
#endif
static uint64 test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timing);
static void output(uint64 loop_count);
 
int
main(int argc, char *argv[])
{
    set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_test_timing"));
    progname = get_progname(argv[0]);
 
    handle_args(argc, argv);
 
    /* initialize timing infrastructure (required for INSTR_* calls) */
    pg_initialize_timing();
 
    test_system_timing();
 
#if PG_INSTR_TSC_CLOCK
    test_tsc_timing();
#endif
 
    return 0;
}
 
static void
handle_args(int argc, char *argv[])
{
    static struct option long_options[] = {
        {"duration", required_argument, NULL, 'd'},
        {"cutoff", required_argument, NULL, 'c'},
        {NULL, 0, NULL, 0}
    };
 
    int         option;         /* Command line option */
    int         optindex = 0;   /* used by getopt_long */
    unsigned long optval;       /* used for option parsing */
    char       *endptr;
 
    if (argc > 1)
    {
        if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
        {
            printf(_("Usage: %s [-d DURATION] [-c CUTOFF]\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:c:",
                                 long_options, &optindex)) != -1)
    {
        switch (option)
        {
            case 'd':
                errno = 0;
                optval = strtoul(optarg, &endptr, 10);
 
                if (endptr == optarg || *endptr != '\0' ||
                    errno != 0 || optval != (unsigned int) optval)
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"),
                            progname, "--duration");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
 
                test_duration = (unsigned int) optval;
                if (test_duration == 0)
                {
                    fprintf(stderr, _("%s: %s must be in range %u..%u\n"),
                            progname, "--duration", 1, UINT_MAX);
                    exit(1);
                }
                break;
 
            case 'c':
                errno = 0;
                max_rprct = strtod(optarg, &endptr);
 
                if (endptr == optarg || *endptr != '\0' || errno != 0)
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"),
                            progname, "--cutoff");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
 
                if (max_rprct < 0 || max_rprct > 100)
                {
                    fprintf(stderr, _("%s: %s must be in range %u..%u\n"),
                            progname, "--cutoff", 0, 100);
                    exit(1);
                }
                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);
    }
 
    printf(ngettext("Testing timing overhead for %u second.\n\n",
                    "Testing timing overhead for %u seconds.\n\n",
                    test_duration),
           test_duration);
}
 
/*
 * This tests default (non-fast) timing code. A clock source for that is
 * always available. Hence, we can unconditionally output the result.
 */
static void
test_system_timing(void)
{
    uint64      loop_count;
 
    loop_count = test_timing(test_duration, TIMING_CLOCK_SOURCE_SYSTEM, false);
    output(loop_count);
}
 
/*
 * If on a supported architecture, test the TSC clock source. This clock
 * source is not always available. In that case we print an informational
 * message indicating as such.
 *
 * We first emit "slow" timings (RDTSCP on x86), which are used for higher
 * precision measurements when the TSC clock source is enabled. We emit
 * "fast" timings second (RDTSC on x86), which is used for faster timing
 * measurements with lower precision.
 */
#if PG_INSTR_TSC_CLOCK
static void
test_tsc_timing(void)
{
    uint64      loop_count;
    uint32      calibrated_freq;
 
    printf("\n");
    loop_count = test_timing(test_duration, TIMING_CLOCK_SOURCE_TSC, false);
    if (loop_count > 0)
    {
        output(loop_count);
        printf("\n");
 
        /* Now, emit fast timing measurements */
        loop_count = test_timing(test_duration, TIMING_CLOCK_SOURCE_TSC, true);
        output(loop_count);
        printf("\n");
 
        printf(_("TSC frequency in use: %u kHz\n"), timing_tsc_frequency_khz);
 
        calibrated_freq = pg_tsc_calibrate_frequency();
        if (calibrated_freq > 0)
            printf(_("TSC frequency from calibration: %u kHz\n"), calibrated_freq);
        else
            printf(_("TSC calibration did not converge\n"));
 
        pg_set_timing_clock_source(TIMING_CLOCK_SOURCE_AUTO);
        if (pg_current_timing_clock_source() == TIMING_CLOCK_SOURCE_TSC)
            printf(_("TSC clock source will be used by default, unless timing_clock_source is set to 'system'.\n"));
        else
            printf(_("TSC clock source will not be used by default, unless timing_clock_source is set to 'tsc'.\n"));
    }
    else
        printf(_("TSC clock source is not usable. Likely unable to determine TSC frequency. Are you running in an unsupported virtualized environment?\n"));
}
#endif
 
static uint64
test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timing)
{
    uint64      loop_count = 0;
    instr_time  start_time,
                end_time,
                prev,
                cur;
    const char *time_source = NULL;
 
    if (!pg_set_timing_clock_source(source))
        return 0;
 
    time_source = PG_INSTR_SYSTEM_CLOCK_NAME;
 
#if PG_INSTR_TSC_CLOCK
    if (pg_current_timing_clock_source() == TIMING_CLOCK_SOURCE_TSC)
        time_source = fast_timing ? PG_INSTR_TSC_CLOCK_NAME_FAST : PG_INSTR_TSC_CLOCK_NAME;
#endif
 
    if (fast_timing)
        printf(_("Fast clock source: %s\n"), time_source);
    else if (source == TIMING_CLOCK_SOURCE_SYSTEM)
        printf(_("System clock source: %s\n"), time_source);
    else
        printf(_("Clock source: %s\n"), time_source);
 
    /*
     * Pre-zero the statistics data structures.  They're already zero by
     * default, but this helps bring them into processor cache and avoid
     * possible timing glitches due to COW behavior.
     */
    memset(direct_histogram, 0, sizeof(direct_histogram));
    memset(histogram, 0, sizeof(histogram));
    largest_diff = 0;
    largest_diff_count = 0;
 
    INSTR_TIME_SET_CURRENT(start_time);
    cur = start_time;
 
    end_time = start_time;
    INSTR_TIME_ADD_NANOSEC(end_time, duration * NS_PER_S);
 
    while (INSTR_TIME_GT(end_time, cur))
    {
        int64       diff;
        int32       bits;
        instr_time  diff_time;
 
        prev = cur;
 
        if (fast_timing)
            INSTR_TIME_SET_CURRENT_FAST(cur);
        else
            INSTR_TIME_SET_CURRENT(cur);
 
        diff_time = cur;
        INSTR_TIME_SUBTRACT(diff_time, prev);
        diff = INSTR_TIME_GET_NANOSEC(diff_time);
 
        /* Did time go backwards? */
        if (unlikely(diff < 0))
        {
            fprintf(stderr, _("Detected clock going backwards in time.\n"));
            fprintf(stderr, _("Time warp: %" PRId64 " ns\n"), diff);
            exit(1);
        }
 
        /* What is the highest bit in the time diff? */
        if (diff > 0)
        {
            bits = pg_leftmost_one_pos64(diff) + 1;
            /* histogram should be defined large enough */
            Assert(bits < lengthof(histogram));
        }
        else
            bits = 0;
 
        /* Update appropriate duration bucket */
        histogram[bits]++;
 
        /* Update direct histogram of time diffs */
        if (diff < NUM_DIRECT)
            direct_histogram[diff]++;
 
        /* Also track the largest observed duration, even if >= NUM_DIRECT */
        if (diff > largest_diff)
        {
            largest_diff = diff;
            largest_diff_count = 1;
        }
        else if (diff == largest_diff)
            largest_diff_count++;
 
        loop_count++;
    }
 
    /* Refresh end time to be the actual time spent (vs the target end time) */
    INSTR_TIME_SET_CURRENT(end_time);
 
    INSTR_TIME_SUBTRACT(end_time, start_time);
 
    printf(_("Average loop time including overhead: %0.2f ns\n"),
           INSTR_TIME_GET_DOUBLE(end_time) * NS_PER_S / loop_count);
 
    return loop_count;
}
 
static void
output(uint64 loop_count)
{
    int         max_bit = lengthof(histogram) - 1;
    const char *header1 = _("<= ns");
    const char *header1b = _("ns");
    const char *header2 = /* xgettext:no-c-format */ _("% of total");
    const char *header3 = /* xgettext:no-c-format */ _("running %");
    const char *header4 = _("count");
    int         len1 = strlen(header1);
    int         len2 = strlen(header2);
    int         len3 = strlen(header3);
    int         len4 = strlen(header4);
    double      rprct;
    bool        stopped = false;
 
    /* find highest bit value */
    while (max_bit > 0 && histogram[max_bit] == 0)
        max_bit--;
 
    /* set minimum column widths */
    len1 = Max(19, len1);
    len2 = Max(10, len2);
    len3 = Max(10, len3);
    len4 = Max(10, len4);
 
    printf(_("Histogram of timing durations:\n"));
    printf("%*s   %*s %*s %*s\n",
           len1, header1,
           len2, header2,
           len3, header3,
           len4, header4);
 
    rprct = 0;
    for (int i = 0; i <= max_bit; i++)
    {
        double      prct = (double) histogram[i] * 100 / loop_count;
 
        rprct += prct;
        printf("%*llu   %*.4f %*.4f %*lld\n",
               len1, (1ULL << i) - 1,
               len2, prct,
               len3, rprct,
               len4, histogram[i]);
    }
 
    printf(_("\nObserved timing durations up to %.4f%%:\n"), max_rprct);
    printf("%*s   %*s %*s %*s\n",
           len1, header1b,
           len2, header2,
           len3, header3,
           len4, header4);
 
    rprct = 0;
    for (int i = 0; i < NUM_DIRECT; i++)
    {
        if (direct_histogram[i])
        {
            double      prct = (double) direct_histogram[i] * 100 / loop_count;
            bool        print_it = !stopped;
 
            rprct += prct;
 
            /* if largest diff is < NUM_DIRECT, be sure we print it */
            if (i == largest_diff)
            {
                if (stopped)
                    printf("...\n");
                print_it = true;
            }
 
            if (print_it)
                printf("%*d   %*.4f %*.4f %*lld\n",
                       len1, i,
                       len2, prct,
                       len3, rprct,
                       len4, direct_histogram[i]);
            if (rprct >= max_rprct)
                stopped = true;
        }
    }
 
    /* print largest diff when it's outside the array range */
    if (largest_diff >= NUM_DIRECT)
    {
        double      prct = (double) largest_diff_count * 100 / loop_count;
 
        printf("...\n");
        printf("%*lld   %*.4f %*.4f %*lld\n",
               len1, (long long) largest_diff,
               len2, prct,
               len3, 100.0,
               len4, largest_diff_count);
    }
}