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pg_test_timing: store timing deltas in int64

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Commit 0b096e379e changed pg_test_timing to measure timing
differences in nanoseconds instead of microseconds, but the resulting
deltas continued to be stored in int32.

That can overflow for large gaps (for example, values greater than about
2.14 seconds in nanoseconds), leading to truncation or incorrect output.

This commit fixes the issue by storing measured timing deltas in int64.
This prevents overflow for large values and better matches
nanosecond-resolution measurements.

Author: Chao Li <lic@highgo.com>
Reviewed-by: Lukas Fittl <lukas@fittl.com>
Reviewed-by: Xiaopeng Wang <wxp_728@163.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/F780CEEB-A237-4302-9F55-60E9D8B6533D@gmail.com
This commit is contained in:
Fujii Masao 2026-04-24 12:11:40 +09:00
parent 94219a73f7
commit 863c4b827d
1 changed files with 17 additions and 13 deletions
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30
src/bin/pg_test_timing/pg_test_timing.c
View file

@ -18,14 +18,14 @@ static unsigned int test_duration = 3;
static double max_rprct = 99.99;
/* record duration in powers of 2 nanoseconds */
static long long int histogram[32];
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 int32 largest_diff;
static int64 largest_diff;
static long long int largest_diff_count;
@ -262,8 +262,8 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
while (INSTR_TIME_GT(end_time, cur))
{
int32 diff,
bits;
int64 diff;
int32 bits;
instr_time diff_time;
prev = cur;
@ -281,13 +281,17 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
if (unlikely(diff < 0))
{
fprintf(stderr, _("Detected clock going backwards in time.\n"));
fprintf(stderr, _("Time warp: %d ns\n"), diff);
fprintf(stderr, _("Time warp: " INT64_FORMAT " ns\n"), diff);
exit(1);
}
/* What is the highest bit in the time diff? */
if (diff > 0)
bits = pg_leftmost_one_pos32(diff) + 1;
{
bits = pg_leftmost_one_pos64(diff) + 1;
/* histogram should be defined large enough */
Assert(bits < lengthof(histogram));
}
else
bits = 0;
@ -316,7 +320,7 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
INSTR_TIME_SUBTRACT(end_time, start_time);
printf(_("Average loop time including overhead: %0.2f ns\n"),
INSTR_TIME_GET_DOUBLE(end_time) * 1e9 / loop_count);
INSTR_TIME_GET_DOUBLE(end_time) * NS_PER_S / loop_count);
return loop_count;
}
@ -324,7 +328,7 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
static void
output(uint64 loop_count)
{
int max_bit = 31;
int max_bit = lengthof(histogram) - 1;
const char *header1 = _("<= ns");
const char *header1b = _("ns");
const char *header2 = /* xgettext:no-c-format */ _("% of total");
@ -342,7 +346,7 @@ output(uint64 loop_count)
max_bit--;
/* set minimum column widths */
len1 = Max(8, len1);
len1 = Max(19, len1);
len2 = Max(10, len2);
len3 = Max(10, len3);
len4 = Max(10, len4);
@ -360,8 +364,8 @@ output(uint64 loop_count)
double prct = (double) histogram[i] * 100 / loop_count;
rprct += prct;
printf("%*ld %*.4f %*.4f %*lld\n",
len1, (1L << i) - 1,
printf("%*llu %*.4f %*.4f %*lld\n",
len1, (1ULL << i) - 1,
len2, prct,
len3, rprct,
len4, histogram[i]);
@ -409,8 +413,8 @@ output(uint64 loop_count)
double prct = (double) largest_diff_count * 100 / loop_count;
printf("...\n");
printf("%*d %*.4f %*.4f %*lld\n",
len1, largest_diff,
printf("%*lld %*.4f %*.4f %*lld\n",
len1, (long long) largest_diff,
len2, prct,
len3, 100.0,
len4, largest_diff_count);