Hi,
On 2/7/23 19:12, Andres Freund wrote:
This fails to build on several platforms:
https://cirrus-ci.com/github/postgresql-cfbot/postgresql/commitfest%2F42%2F3751
I think I fixed the compilation errors. It was due to a few variables
being declared under
#if defined(__x86_64__) && defined(__linux__)
while being used also under non x86 Linux.
I also removed again the code to obtain the TSC frequency under
hypervisors because the TSC is usually emulated and therefore no faster
than clock_gettime() anyways. So we now simply fallback to
clock_gettime() on hypervisors when we cannot obtain the frequency via
leaf 0x16.
Beyond that I reviewed the first two patches a while ago in [1]. I hope
we can progress with them to further reduce the size of this patch set.
[1]
https://www.postgresql.org/message-id/3ac157f7-085d-e071-45fc-b87cd306360c%40gmail.com
--
David Geier
(ServiceNow)
From 36ff7f7ee14bf42ef0fb775cec428180251c3ff9 Mon Sep 17 00:00:00 2001
From: Andres Freund <and...@anarazel.de>
Date: Fri, 20 Jan 2023 15:31:54 -0800
Subject: [PATCH v8 1/3] instr_time: Add INSTR_TIME_SET_SECONDS(),
INSTR_TIME_IS_LT()
INSTR_TIME_SET_SECONDS() is useful to calculate the end of a time-bound loop
without having to convert into time units (which is
costly). INSTR_TIME_IS_LT() can be used to check the loop condition.
Author:
Reviewed-by:
Discussion: https://postgr.es/m/
Backpatch:
---
src/include/portability/instr_time.h | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/src/include/portability/instr_time.h b/src/include/portability/instr_time.h
index cc85138e21..aab80effb0 100644
--- a/src/include/portability/instr_time.h
+++ b/src/include/portability/instr_time.h
@@ -15,6 +15,8 @@
*
* INSTR_TIME_IS_ZERO(t) is t equal to zero?
*
+ * INSTR_TIME_IS_LT(x, y) x < y
+ *
* INSTR_TIME_SET_ZERO(t) set t to zero (memset is acceptable too)
*
* INSTR_TIME_SET_CURRENT(t) set t to current time
@@ -22,6 +24,8 @@
* INSTR_TIME_SET_CURRENT_LAZY(t) set t to current time if t is zero,
* evaluates to whether t changed
*
+ * INSTR_TIME_SET_SECONDS(t, s) set t to s seconds
+ *
* INSTR_TIME_ADD(x, y) x += y
*
* INSTR_TIME_SUBTRACT(x, y) x -= y
@@ -122,6 +126,9 @@ pg_clock_gettime_ns(void)
#define INSTR_TIME_SET_CURRENT(t) \
((t) = pg_clock_gettime_ns())
+#define INSTR_TIME_SET_SECONDS(t, s) \
+ ((t).ticks = NS_PER_S * (s))
+
#define INSTR_TIME_GET_NANOSEC(t) \
((int64) (t).ticks)
@@ -156,6 +163,9 @@ GetTimerFrequency(void)
#define INSTR_TIME_SET_CURRENT(t) \
((t) = pg_query_performance_counter())
+#define INSTR_TIME_SET_SECONDS(t, s) \
+ ((t).ticks = s * GetTimerFrequency())
+
#define INSTR_TIME_GET_NANOSEC(t) \
((int64) ((t).ticks * ((double) NS_PER_S / GetTimerFrequency())))
@@ -168,6 +178,8 @@ GetTimerFrequency(void)
#define INSTR_TIME_IS_ZERO(t) ((t).ticks == 0)
+#define INSTR_TIME_IS_LT(x, y) ((x).ticks < (y).ticks)
+
#define INSTR_TIME_SET_ZERO(t) ((t).ticks = 0)
--
2.34.1
From 1200bfee5b8ebf7c68d8cefb3771a4c3523c2cea Mon Sep 17 00:00:00 2001
From: Andres Freund <and...@anarazel.de>
Date: Mon, 16 Jan 2023 11:19:11 -0800
Subject: [PATCH v8 2/3] wip: report nanoseconds in pg_test_timing
This commit also updates pg_test_timing's documentation:
- compare EXPLAIN (ANALYZE, TIMING ON/OFF) instead of comparing performance of
of statement with/without EXPLAIN ANALYZE
- explain the 2x overhead (due to two timestamp acquisitions per row)
- remove old section about old versions of linux - I couldn't update the
numbers, and it's old enough nobody would care
---
doc/src/sgml/ref/pgtesttiming.sgml | 117 ++++++++++--------------
src/bin/pg_test_timing/pg_test_timing.c | 74 +++++++++------
2 files changed, 95 insertions(+), 96 deletions(-)
diff --git a/doc/src/sgml/ref/pgtesttiming.sgml b/doc/src/sgml/ref/pgtesttiming.sgml
index a5eb3aa25e..7e0266cf58 100644
--- a/doc/src/sgml/ref/pgtesttiming.sgml
+++ b/doc/src/sgml/ref/pgtesttiming.sgml
@@ -93,28 +93,34 @@ PostgreSQL documentation
<para>
Good results will show most (>90%) individual timing calls take less than
- one microsecond. Average per loop overhead will be even lower, below 100
- nanoseconds. This example from an Intel i7-860 system using a TSC clock
- source shows excellent performance:
+ one microsecond (1000 nanoseconds). Average per loop overhead will be even
+ lower, below 100 nanoseconds. This example from an Intel i9-9880H system
+ using a TSC clock source shows excellent performance:
<screen><![CDATA[
Testing timing overhead for 3 seconds.
-Per loop time including overhead: 35.96 ns
+Per loop time including overhead: 13.74 ns
Histogram of timing durations:
- < us % of total count
- 1 96.40465 80435604
- 2 3.59518 2999652
- 4 0.00015 126
- 8 0.00002 13
- 16 0.00000 2
+ < ns % of total count
+ 16 97.00221 211857215
+ 32 2.99555 6542412
+ 64 0.00115 2505
+ 128 0.00035 759
+ 256 0.00004 78
+ 512 0.00000 3
+ 1024 0.00000 4
+ 2048 0.00034 732
+ 4096 0.00000 6
+ 8192 0.00000 8
+ 16384 0.00019 409
+ 32768 0.00018 403
+ 65536 0.00000 1
]]></screen>
</para>
<para>
- Note that different units are used for the per loop time than the
- histogram. The loop can have resolution within a few nanoseconds (ns),
- while the individual timing calls can only resolve down to one microsecond
- (us).
+ Note that the accuracy of the histogram entries may be lower than the
+ per loop time.
</para>
</refsect2>
@@ -125,24 +131,25 @@ Histogram of timing durations:
When the query executor is running a statement using
<command>EXPLAIN ANALYZE</command>, individual operations are timed as well
as showing a summary. The overhead of your system can be checked by
- counting rows with the <application>psql</application> program:
+ disabling the per-row timing, using the <literal>TIMING OFF</literal>
+ option:
<screen>
-CREATE TABLE t AS SELECT * FROM generate_series(1,100000);
-\timing
-SELECT COUNT(*) FROM t;
-EXPLAIN ANALYZE SELECT COUNT(*) FROM t;
+CREATE TABLE t AS SELECT * FROM generate_series(1, 100000);
+EXPLAIN (ANALYZE, TIMING OFF) SELECT COUNT(*) FROM t;
+EXPLAIN (ANALYZE, TIMING ON) SELECT COUNT(*) FROM t;
</screen>
</para>
<para>
- The i7-860 system measured runs the count query in 9.8 ms while
- the <command>EXPLAIN ANALYZE</command> version takes 16.6 ms, each
- processing just over 100,000 rows. That 6.8 ms difference means the timing
- overhead per row is 68 ns, about twice what pg_test_timing estimated it
- would be. Even that relatively small amount of overhead is making the fully
- timed count statement take almost 70% longer. On more substantial queries,
- the timing overhead would be less problematic.
+ The i9-9880H system measured shows an execution time of 4.116 ms for the
+ <literal>TIMING OFF</literal> query, and 6.965 ms for the
+ <literal>TIMING ON</literal>, each processing 100,000 rows.
+
+ That 2.849 ms difference means the timing overhead per row is 28 ns. As
+ <literal>TIMING ON</literal> measures timestamps twice per row returned by
+ an executor node, the overhead is very close to what pg_test_timing
+ estimated it would be.
</para>
</refsect2>
@@ -157,28 +164,31 @@ EXPLAIN ANALYZE SELECT COUNT(*) FROM t;
<screen><![CDATA[
# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
-tsc hpet acpi_pm
+tsc acpi_pm
# echo acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource
# pg_test_timing
-Per loop time including overhead: 722.92 ns
+Testing timing overhead for 3 seconds.
+Per loop time including overhead: 708.58 ns
Histogram of timing durations:
- < us % of total count
- 1 27.84870 1155682
- 2 72.05956 2990371
- 4 0.07810 3241
- 8 0.01357 563
- 16 0.00007 3
+ < ns % of total count
+ 1024 99.79796 4225270
+ 2048 0.15560 6588
+ 4096 0.00035 15
+ 8192 0.01738 736
+ 16384 0.01679 711
+ 32768 0.01190 504
]]></screen>
</para>
<para>
In this configuration, the sample <command>EXPLAIN ANALYZE</command> above
- takes 115.9 ms. That's 1061 ns of timing overhead, again a small multiple
- of what's measured directly by this utility. That much timing overhead
- means the actual query itself is only taking a tiny fraction of the
- accounted for time, most of it is being consumed in overhead instead. In
- this configuration, any <command>EXPLAIN ANALYZE</command> totals involving
- many timed operations would be inflated significantly by timing overhead.
+ shows an execution time of 148.7 ms. That's 1392 ns of per-row timing
+ overhead. Taking the two timestamps per row into account, that's again
+ close to what pg_test_timing estimated. That much timing overhead means
+ the actual query itself is only taking a tiny fraction of the accounted for
+ time, most of it is being consumed in overhead instead. In this
+ configuration, any <command>EXPLAIN ANALYZE</command> totals involving many
+ timed operations would be inflated significantly by timing overhead.
</para>
<para>
@@ -196,33 +206,6 @@ kern.timecounter.hardware: ACPI-fast -> TSC
</screen>
</para>
- <para>
- Other systems may only allow setting the time source on boot. On older
- Linux systems the "clock" kernel setting is the only way to make this sort
- of change. And even on some more recent ones, the only option you'll see
- for a clock source is "jiffies". Jiffies are the older Linux software clock
- implementation, which can have good resolution when it's backed by fast
- enough timing hardware, as in this example:
-
-<screen><![CDATA[
-$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
-jiffies
-$ dmesg | grep time.c
-time.c: Using 3.579545 MHz WALL PM GTOD PIT/TSC timer.
-time.c: Detected 2400.153 MHz processor.
-$ pg_test_timing
-Testing timing overhead for 3 seconds.
-Per timing duration including loop overhead: 97.75 ns
-Histogram of timing durations:
- < us % of total count
- 1 90.23734 27694571
- 2 9.75277 2993204
- 4 0.00981 3010
- 8 0.00007 22
- 16 0.00000 1
- 32 0.00000 1
-]]></screen></para>
-
</refsect2>
<refsect2>
diff --git a/src/bin/pg_test_timing/pg_test_timing.c b/src/bin/pg_test_timing/pg_test_timing.c
index c29d6f8762..e20718669a 100644
--- a/src/bin/pg_test_timing/pg_test_timing.c
+++ b/src/bin/pg_test_timing/pg_test_timing.c
@@ -19,8 +19,8 @@ static void handle_args(int argc, char *argv[]);
static uint64 test_timing(unsigned int duration);
static void output(uint64 loop_count);
-/* record duration in powers of 2 microseconds */
-long long int histogram[32];
+/* record duration in powers of 2 nanoseconds */
+uint64 histogram[64];
int
main(int argc, char *argv[])
@@ -121,35 +121,48 @@ handle_args(int argc, char *argv[])
static uint64
test_timing(unsigned int duration)
{
- uint64 total_time;
- int64 time_elapsed = 0;
uint64 loop_count = 0;
- uint64 prev,
- cur;
+ instr_time until_time,
+ total_time;
instr_time start_time,
- end_time,
- temp;
-
- total_time = duration > 0 ? duration * INT64CONST(1000000) : 0;
+ end_time;
+ instr_time cur;
INSTR_TIME_SET_CURRENT(start_time);
- cur = INSTR_TIME_GET_MICROSEC(start_time);
- while (time_elapsed < total_time)
+ /*
+ * To reduce loop overhead, check loop condition in instr_time domain.
+ */
+ INSTR_TIME_SET_SECONDS(total_time, duration);
+ until_time = start_time;
+ INSTR_TIME_ADD(until_time, total_time);
+
+ cur = start_time;
+
+ while (INSTR_TIME_IS_LT(cur, until_time))
{
- int32 diff,
- bits = 0;
+ instr_time temp;
+ instr_time prev;
+ int64 diff;
+ int32 bits = 0;
prev = cur;
- INSTR_TIME_SET_CURRENT(temp);
- cur = INSTR_TIME_GET_MICROSEC(temp);
- diff = cur - prev;
+ INSTR_TIME_SET_CURRENT(cur);
+ temp = cur;
+ INSTR_TIME_SUBTRACT(temp, prev);
+ diff = INSTR_TIME_GET_NANOSEC(temp);
/* Did time go backwards? */
- if (diff < 0)
+ if (unlikely(diff <= 0))
{
+ /* can't do anything with that measurement */
+ if (diff == 0)
+ {
+ loop_count++;
+ continue;
+ }
fprintf(stderr, _("Detected clock going backwards in time.\n"));
- fprintf(stderr, _("Time warp: %d ms\n"), diff);
+ fprintf(stderr, _("Time warp: %lld ns\n"), (long long) diff);
exit(1);
}
@@ -164,8 +177,6 @@ test_timing(unsigned int duration)
histogram[bits]++;
loop_count++;
- INSTR_TIME_SUBTRACT(temp, start_time);
- time_elapsed = INSTR_TIME_GET_MICROSEC(temp);
}
INSTR_TIME_SET_CURRENT(end_time);
@@ -173,7 +184,7 @@ test_timing(unsigned int duration)
INSTR_TIME_SUBTRACT(end_time, start_time);
printf(_("Per 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;
}
@@ -181,9 +192,10 @@ test_timing(unsigned int duration)
static void
output(uint64 loop_count)
{
- int64 max_bit = 31,
+ int64 low_bit = 0,
+ max_bit = 63,
i;
- char *header1 = _("< us");
+ char *header1 = _("< ns");
char *header2 = /* xgettext:no-c-format */ _("% of total");
char *header3 = _("count");
int len1 = strlen(header1);
@@ -194,15 +206,19 @@ output(uint64 loop_count)
while (max_bit > 0 && histogram[max_bit] == 0)
max_bit--;
+ /* find lowest bit value */
+ while (low_bit < max_bit && histogram[low_bit] == 0)
+ low_bit++;
+
printf(_("Histogram of timing durations:\n"));
printf("%*s %*s %*s\n",
- Max(6, len1), header1,
+ Max(9, len1), header1,
Max(10, len2), header2,
Max(10, len3), header3);
- for (i = 0; i <= max_bit; i++)
- printf("%*ld %*.5f %*lld\n",
- Max(6, len1), 1l << i,
+ for (i = low_bit; i <= max_bit; i++)
+ printf("%*ld %*.5f %*llu\n",
+ Max(9, len1), 1l << i,
Max(10, len2) - 1, (double) histogram[i] * 100 / loop_count,
- Max(10, len3), histogram[i]);
+ Max(10, len3), (long long unsigned) histogram[i]);
}
--
2.34.1
From c3c90049579af7cb9c12d7baa0301f9759d20abf Mon Sep 17 00:00:00 2001
From: David Geier <geidav...@gmail.com>
Date: Mon, 23 Jan 2023 18:13:55 +0100
Subject: [PATCH v8 3/3] Use RDTSC(P) instructions to measure time on x86 Linux
For now this is only enabled on Linux/x86 when the system clocksource is
marked TSC as well, as determined at runtime. This way we can rely on the
Linux kernel to make a decision whether TSC is invariant and usable on the
current CPU architecture. In all other cases we continue to use the
clock_gettime() implementation like before.
Note that we intentionally use RDTSC, not RDTSCP, as RDTSCP waits for
currently running CPU instructions to have retired. This adds up to
noticable latency for little benefit in the typical InstrStartNode() /
InstrStopNode() use case. The macro to be used for these cases is
called INSTR_TIME_SET_CURRENT_FAST(). The original macro
INSTR_TIME_SET_CURRENT() uses RDTSCP and is supposed to be used when
precision is more important than performance.
---
src/backend/access/heap/vacuumlazy.c | 3 +-
src/backend/commands/explain.c | 2 +-
src/backend/executor/instrument.c | 12 ++-
src/backend/utils/init/postinit.c | 3 +
src/bin/pg_test_timing/pg_test_timing.c | 7 +-
src/bin/pgbench/pgbench.c | 3 +
src/bin/psql/startup.c | 4 +
src/common/Makefile | 1 +
src/common/instr_time.c | 130 ++++++++++++++++++++++++
src/common/meson.build | 1 +
src/include/portability/instr_time.h | 130 ++++++++++++++++++++----
src/tools/msvc/Mkvcbuild.pm | 2 +-
12 files changed, 266 insertions(+), 32 deletions(-)
create mode 100644 src/common/instr_time.c
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 8f14cf85f3..212093568b 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -3002,8 +3002,7 @@ count_nondeletable_pages(LVRelState *vacrel, bool *lock_waiter_detected)
INSTR_TIME_SET_CURRENT(currenttime);
elapsed = currenttime;
INSTR_TIME_SUBTRACT(elapsed, starttime);
- if ((INSTR_TIME_GET_MICROSEC(elapsed) / 1000)
- >= VACUUM_TRUNCATE_LOCK_CHECK_INTERVAL)
+ if (INSTR_TIME_GET_MILLISEC(elapsed) >= VACUUM_TRUNCATE_LOCK_CHECK_INTERVAL)
{
if (LockHasWaitersRelation(vacrel->rel, AccessExclusiveLock))
{
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index fbbf28cf06..c4243bc668 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -526,7 +526,7 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
double totaltime = 0;
int eflags;
int instrument_option = 0;
-
+
Assert(plannedstmt->commandType != CMD_UTILITY);
if (es->analyze && es->timing)
diff --git a/src/backend/executor/instrument.c b/src/backend/executor/instrument.c
index ee78a5749d..1ce3d62cff 100644
--- a/src/backend/executor/instrument.c
+++ b/src/backend/executor/instrument.c
@@ -67,9 +67,13 @@ InstrInit(Instrumentation *instr, int instrument_options)
void
InstrStartNode(Instrumentation *instr)
{
- if (instr->need_timer &&
- !INSTR_TIME_SET_CURRENT_LAZY(instr->starttime))
- elog(ERROR, "InstrStartNode called twice in a row");
+ if (instr->need_timer)
+ {
+ if (!INSTR_TIME_IS_ZERO(instr->starttime))
+ elog(ERROR, "InstrStartNode called twice in a row");
+ else
+ INSTR_TIME_SET_CURRENT_FAST(instr->starttime);
+ }
/* save buffer usage totals at node entry, if needed */
if (instr->need_bufusage)
@@ -95,7 +99,7 @@ InstrStopNode(Instrumentation *instr, double nTuples)
if (INSTR_TIME_IS_ZERO(instr->starttime))
elog(ERROR, "InstrStopNode called without start");
- INSTR_TIME_SET_CURRENT(endtime);
+ INSTR_TIME_SET_CURRENT_FAST(endtime);
INSTR_TIME_ACCUM_DIFF(instr->counter, endtime, instr->starttime);
INSTR_TIME_SET_ZERO(instr->starttime);
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 2f07ca7a0e..2eef902483 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -805,6 +805,9 @@ InitPostgres(const char *in_dbname, Oid dboid,
/* Initialize portal manager */
EnablePortalManager();
+ /* initialize high-precision interval timing */
+ INSTR_TIME_INITIALIZE();
+
/* Initialize status reporting */
pgstat_beinit();
diff --git a/src/bin/pg_test_timing/pg_test_timing.c b/src/bin/pg_test_timing/pg_test_timing.c
index e20718669a..d185c8fe2e 100644
--- a/src/bin/pg_test_timing/pg_test_timing.c
+++ b/src/bin/pg_test_timing/pg_test_timing.c
@@ -128,7 +128,8 @@ test_timing(unsigned int duration)
end_time;
instr_time cur;
- INSTR_TIME_SET_CURRENT(start_time);
+ INSTR_TIME_INITIALIZE();
+ INSTR_TIME_SET_CURRENT_FAST(start_time);
/*
* To reduce loop overhead, check loop condition in instr_time domain.
@@ -147,7 +148,7 @@ test_timing(unsigned int duration)
int32 bits = 0;
prev = cur;
- INSTR_TIME_SET_CURRENT(cur);
+ INSTR_TIME_SET_CURRENT_FAST(cur);
temp = cur;
INSTR_TIME_SUBTRACT(temp, prev);
diff = INSTR_TIME_GET_NANOSEC(temp);
@@ -179,7 +180,7 @@ test_timing(unsigned int duration)
loop_count++;
}
- INSTR_TIME_SET_CURRENT(end_time);
+ INSTR_TIME_SET_CURRENT_FAST(end_time);
INSTR_TIME_SUBTRACT(end_time, start_time);
diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index 508ed218e8..4125bc8cb7 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -7059,6 +7059,9 @@ main(int argc, char **argv)
initRandomState(&state[i].cs_func_rs);
}
+ /* initialize high-precision interval timing */
+ INSTR_TIME_INITIALIZE();
+
/* opening connection... */
con = doConnect();
if (con == NULL)
diff --git a/src/bin/psql/startup.c b/src/bin/psql/startup.c
index 5a28b6f713..3f95e01320 100644
--- a/src/bin/psql/startup.c
+++ b/src/bin/psql/startup.c
@@ -24,6 +24,7 @@
#include "help.h"
#include "input.h"
#include "mainloop.h"
+#include "portability/instr_time.h"
#include "settings.h"
/*
@@ -322,6 +323,9 @@ main(int argc, char *argv[])
PQsetNoticeProcessor(pset.db, NoticeProcessor, NULL);
+ /* initialize high-precision interval timing */
+ INSTR_TIME_INITIALIZE();
+
SyncVariables();
if (options.list_dbs)
diff --git a/src/common/Makefile b/src/common/Makefile
index 113029bf7b..23a5c68705 100644
--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -59,6 +59,7 @@ OBJS_COMMON = \
file_perm.o \
file_utils.o \
hashfn.o \
+ instr_time.o \
ip.o \
jsonapi.o \
keywords.o \
diff --git a/src/common/instr_time.c b/src/common/instr_time.c
new file mode 100644
index 0000000000..998fb30e2f
--- /dev/null
+++ b/src/common/instr_time.c
@@ -0,0 +1,130 @@
+/*-------------------------------------------------------------------------
+ *
+ * instr_time.c
+ * Non-inline parts of the portable high-precision interval timing
+ * implementation
+ *
+ * Portions Copyright (c) 2022, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ * src/backend/port/instr_time.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "portability/instr_time.h"
+
+#ifndef WIN32
+/*
+ * Stores what the number of cycles needs to be multiplied with to end up
+ * with nanoseconds using integer math. See comment in pg_initialize_rdtsc()
+ * for more details.
+ *
+ * By default assume we are using clock_gettime() as a fallback which uses
+ * nanoseconds as ticks. Hence, we set the multiplier to the precision scalar
+ * so that the division in INSTR_TIME_GET_NANOSEC() won't change the nanoseconds.
+ *
+ * When using the RDTSC instruction directly this is filled in during initialization
+ * based on the relevant CPUID fields.
+ */
+int64 ticks_per_ns_scaled = TICKS_TO_NS_PRECISION;
+int64 ticks_per_sec = NS_PER_S;
+int64 max_ticks_no_overflow = PG_INT64_MAX / TICKS_TO_NS_PRECISION;
+
+#if defined(__x86_64__) && defined(__linux__)
+/*
+ * Indicates if RDTSC can be used (Linux/x86 only, when OS uses TSC clocksource)
+ */
+bool has_rdtsc = false;
+
+/*
+ * Indicates if RDTSCP can be used. True if RDTSC can be used and RDTSCP is available.
+ */
+bool has_rdtscp = false;
+
+/*
+ * This fails on hypervisors. On hypervisors a different CPUID leaf could be used
+ * to obtain the TSC frequency. We don't do that because the TSC on hypervisors
+ * is usually emulated and the performance of emulated an TSC is usually as bad as
+ * the performance of the hypervisor's clock_gettime() implementation.
+ */
+static bool get_tsc_frequency_khz(uint32 *tsc_freq)
+{
+ uint32 r0, r1, r2;
+ int result = __get_cpuid(0x16, tsc_freq, &r0, &r1, &r2);
+ *tsc_freq *= 1000; // Convert from MHz to KHz
+ return result > 0 && *tsc_freq > 0;
+}
+
+static bool is_rdtscp_available()
+{
+ uint32 r0, r1, r2, r3;
+ return __get_cpuid(0x80000001, &r0, &r1, &r2, &r3) > 0 && (r3 & (1 << 27)) != 0;
+}
+
+/*
+ * Decide whether we use the RDTSC instruction at runtime, for Linux/x86,
+ * instead of incurring the overhead of a full clock_gettime() call.
+ *
+ * This can't be reliably determined at compile time, since the
+ * availability of an "invariant" TSC (that is not affected by CPU
+ * frequency changes) is dependent on the CPU architecture. Additionally,
+ * there are cases where TSC availability is impacted by virtualization,
+ * where a simple cpuid feature check would not be enough.
+ *
+ * Since Linux already does a significant amount of work to determine
+ * whether TSC is a viable clock source, decide based on that.
+ */
+void pg_initialize_rdtsc(void)
+{
+ FILE *fp = fopen("/sys/devices/system/clocksource/clocksource0/current_clocksource", "r");
+
+ if (fp)
+ {
+ char buf[128];
+
+ if (fgets(buf, sizeof(buf), fp) != NULL && strcmp(buf, "tsc\n") == 0)
+ {
+ /*
+ * Compute baseline CPU peformance, determines speed at which RDTSC advances.
+ */
+ uint32 tsc_freq;
+
+ if (get_tsc_frequency_khz(&tsc_freq))
+ {
+ /*
+ * Ticks to nanoseconds conversion requires floating point math
+ * because because:
+ *
+ * sec = ticks / frequency_hz
+ * ns = ticks / frequency_hz * 1,000,000,000
+ * ns = ticks * (1,000,000,000 / frequency_hz)
+ * ns = ticks * (1,000,000 / frequency_khz) <-- now in kilohertz
+ *
+ * Here, 'ns' is usually a floating number. For example for a 2.5 GHz
+ * CPU the scaling factor becomes 1,000,000 / 2,500,000 = 1.2.
+ *
+ * To be able to use integer math we work around the lack of precision.
+ * We first scale the integer up and after the multiplication by the
+ * number of ticks in INSTR_TIME_GET_NANOSEC() we divide again by the
+ * same value. We picked the scaler such that it provides enough precision
+ * and is a power-of-two which allows for shifting instead of doing an
+ * integer division.
+ */
+ ticks_per_ns_scaled = INT64CONST(1000000) * TICKS_TO_NS_PRECISION / tsc_freq;
+ ticks_per_sec = tsc_freq * 1000; // KHz -> Hz
+ max_ticks_no_overflow = PG_INT64_MAX / ticks_per_ns_scaled;
+
+ has_rdtsc = true;
+ has_rdtscp = is_rdtscp_available();
+ }
+ }
+
+ fclose(fp);
+ }
+}
+#endif /* defined(__x86_64__) && defined(__linux__) */
+
+#endif /* WIN32 */
diff --git a/src/common/meson.build b/src/common/meson.build
index 41bd58ebdf..000983c6bf 100644
--- a/src/common/meson.build
+++ b/src/common/meson.build
@@ -11,6 +11,7 @@ common_sources = files(
'file_perm.c',
'file_utils.c',
'hashfn.c',
+ 'instr_time.c',
'ip.c',
'jsonapi.c',
'keywords.c',
diff --git a/src/include/portability/instr_time.h b/src/include/portability/instr_time.h
index aab80effb0..6fda565366 100644
--- a/src/include/portability/instr_time.h
+++ b/src/include/portability/instr_time.h
@@ -4,9 +4,11 @@
* portable high-precision interval timing
*
* This file provides an abstraction layer to hide portability issues in
- * interval timing. On Unix we use clock_gettime(), and on Windows we use
- * QueryPerformanceCounter(). These macros also give some breathing room to
- * use other high-precision-timing APIs.
+ * interval timing. On Linux/x86 we use the rdtsc instruction when a TSC
+ * clocksource is also used on the host OS. Otherwise, and on other
+ * Unix-like systems we use clock_gettime() and on Windows we use
+ * QueryPerformanceCounter(). These macros also give some breathing
+ * room to use other high-precision-timing APIs.
*
* The basic data type is instr_time, which all callers should treat as an
* opaque typedef. instr_time can store either an absolute time (of
@@ -19,10 +21,11 @@
*
* INSTR_TIME_SET_ZERO(t) set t to zero (memset is acceptable too)
*
- * INSTR_TIME_SET_CURRENT(t) set t to current time
- *
- * INSTR_TIME_SET_CURRENT_LAZY(t) set t to current time if t is zero,
- * evaluates to whether t changed
+ * INSTR_TIME_SET_CURRENT_FAST(t) set t to current time without waiting
+ * for instructions in out-of-order window
+ *
+ * INSTR_TIME_SET_CURRENT(t) set t to current time while waiting for
+ * instructions in OOO to retire
*
* INSTR_TIME_SET_SECONDS(t, s) set t to s seconds
*
@@ -84,7 +87,15 @@ typedef struct instr_time
#ifndef WIN32
+/*
+ * Make sure this is a power-of-two, so that the compiler can turn the
+ * multiplications and divisions into shifts.
+ */
+#define TICKS_TO_NS_PRECISION (1<<14)
+extern int64 ticks_per_ns_scaled;
+extern int64 ticks_per_sec;
+extern int64 max_ticks_no_overflow;
/* Use clock_gettime() */
@@ -110,35 +121,113 @@ typedef struct instr_time
#define PG_INSTR_CLOCK CLOCK_REALTIME
#endif
-/* helper for INSTR_TIME_SET_CURRENT */
+#if defined(__x86_64__) && defined(__linux__)
+#include <x86intrin.h>
+#include <cpuid.h>
+
+extern bool has_rdtsc;
+extern bool has_rdtscp;
+#endif
+
static inline instr_time
-pg_clock_gettime_ns(void)
+pg_clock_gettime()
{
instr_time now;
struct timespec tmp;
clock_gettime(PG_INSTR_CLOCK, &tmp);
now.ticks = tmp.tv_sec * NS_PER_S + tmp.tv_nsec;
-
return now;
}
+static inline instr_time
+pg_get_ticks_fast(void)
+{
+#if defined(__x86_64__) && defined(__linux__)
+ if (has_rdtsc)
+ {
+ instr_time now;
+ uint32 a;
+ now.ticks = __rdtscp(&a);
+ return now;
+ }
+#endif
+
+ return pg_clock_gettime();
+}
+
+static inline instr_time
+pg_get_ticks(void)
+{
+#if defined(__x86_64__) && defined(__linux__)
+ if (has_rdtscp)
+ {
+ instr_time now;
+ uint32 unused;
+ now.ticks = __rdtscp(&unused);
+ return now;
+ }
+#endif
+
+ return pg_clock_gettime();
+}
+
+static inline int64_t
+pg_ticks_to_ns(instr_time t)
+{
+ /*
+ * Would multiplication overflow? If so perform computation in two parts.
+ * Check overflow without actually overflowing via:
+ * a * b > max <=> a > max / b
+ */
+ int64 ns = 0;
+
+ if (unlikely(t.ticks > max_ticks_no_overflow))
+ {
+ /*
+ * Compute how often the maximum number of ticks fits completely into the
+ * number of elapsed ticks and convert that number into nanoseconds.
+ * Then multiply by the count to arrive at the final value. In a 2nd step
+ * we adjust the number of elapsed ticks and convert the remaining ticks.
+ */
+ int64 count = t.ticks / max_ticks_no_overflow;
+ int64 max_ns = max_ticks_no_overflow * ticks_per_ns_scaled / TICKS_TO_NS_PRECISION;
+ ns = max_ns * count;
+
+ /*
+ * Subtract the ticks that we now already accounted for, so that they don't
+ * get counted twice.
+ */
+ t.ticks -= count * max_ticks_no_overflow;
+ Assert(t.ticks >= 0);
+ }
+
+ ns += t.ticks * ticks_per_ns_scaled / TICKS_TO_NS_PRECISION;
+ return ns;
+}
+
+extern void pg_initialize_rdtsc(void);
+
+#define INSTR_TIME_INITIALIZE() \
+ pg_initialize_rdtsc()
+
+#define INSTR_TIME_SET_CURRENT_FAST(t) \
+ ((t) = pg_get_ticks_fast())
+
#define INSTR_TIME_SET_CURRENT(t) \
- ((t) = pg_clock_gettime_ns())
+ ((t) = pg_get_ticks())
#define INSTR_TIME_SET_SECONDS(t, s) \
- ((t).ticks = NS_PER_S * (s))
+ ((t).ticks = (s) * ticks_per_sec)
#define INSTR_TIME_GET_NANOSEC(t) \
- ((int64) (t).ticks)
-
+ pg_ticks_to_ns(t)
#else /* WIN32 */
/* Use QueryPerformanceCounter() */
-/* helper for INSTR_TIME_SET_CURRENT */
static inline instr_time
pg_query_performance_counter(void)
{
@@ -160,6 +249,11 @@ GetTimerFrequency(void)
return (double) f.QuadPart;
}
+#define INSTR_TIME_INITIALIZE()
+
+#define INSTR_TIME_SET_CURRENT_FAST(t) \
+ ((t) = pg_query_performance_counter())
+
#define INSTR_TIME_SET_CURRENT(t) \
((t) = pg_query_performance_counter())
@@ -180,13 +274,8 @@ GetTimerFrequency(void)
#define INSTR_TIME_IS_LT(x, y) ((x).ticks < (y).ticks)
-
#define INSTR_TIME_SET_ZERO(t) ((t).ticks = 0)
-#define INSTR_TIME_SET_CURRENT_LAZY(t) \
- (INSTR_TIME_IS_ZERO(t) ? INSTR_TIME_SET_CURRENT(t), true : false)
-
-
#define INSTR_TIME_ADD(x,y) \
((x).ticks += (y).ticks)
@@ -196,7 +285,6 @@ GetTimerFrequency(void)
#define INSTR_TIME_ACCUM_DIFF(x,y,z) \
((x).ticks += (y).ticks - (z).ticks)
-
#define INSTR_TIME_GET_DOUBLE(t) \
((double) INSTR_TIME_GET_NANOSEC(t) / NS_PER_S)
diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm
index f1c9ddf4a0..bec74b52ae 100644
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -135,7 +135,7 @@ sub mkvcbuild
our @pgcommonallfiles = qw(
archive.c base64.c checksum_helper.c compression.c
config_info.c controldata_utils.c d2s.c encnames.c exec.c
- f2s.c file_perm.c file_utils.c hashfn.c ip.c jsonapi.c
+ f2s.c file_perm.c file_utils.c hashfn.c ip.c instr_time.o jsonapi.c
keywords.c kwlookup.c link-canary.c md5_common.c percentrepl.c
pg_get_line.c pg_lzcompress.c pg_prng.c pgfnames.c psprintf.c relpath.c
rmtree.c saslprep.c scram-common.c string.c stringinfo.c unicode_norm.c
--
2.34.1
