Hi Haibo, On Sat, Apr 11, 2026 at 11:04 PM Haibo Yan <[email protected]> wrote: > > Thanks for the patch. I may be missing something, but I wonder if the new > debug path can still end up calling pg_tsc_calibrate_frequency() after > tsc_detect_frequency() already bailed out with no rdtscp or not invariant. > If so, it seems the diagnostics path is no longer following the same gate as > the normal TSC-usability path, and could still execute pg_rdtscp() while only > trying to print debug info. > Maybe I am overlooking a guard somewhere, but I think it would be safer > either to use the same prerequisites here, or keep this helper purely passive.
Yes, that's a good point. I don't think the TSC not being invariant would be a problem on its own, but the RDTSCP instruction not being available would presumably make the frequency function fail. I think the easiest way to approach that is to only run the calibration function in the debug path when we have a frequency, but it wasn't determined through calibration. Per earlier note from Andres running calibration in those cases is intentional to help us compare CPUID data with what we got from calibration. Attached v28, which also adds the exit(1) mentioned earlier. FWIW, for archive's sake, drongo is green again now, thanks to commit 7fc36c5db550 (Avoid CPUID 0x15/0x16 for Hypervisor TSC frequency). Thanks, Lukas -- Lukas Fittl
From 36f94fa0a224ebf4276146c777214486bf109a85 Mon Sep 17 00:00:00 2001 From: Lukas Fittl <[email protected]> Date: Wed, 8 Apr 2026 10:11:56 -0700 Subject: [PATCH v28] pg_test_timing: Show additional TSC clock source debug info In some cases its needed to understand whether TSC frequency data was sourced from CPUID, and which of the registers. This shows this debug information at the end of pg_test_timing, through use of a new pg_timing_tsc_clock_source_info function, replacing the previous pg_tsc_calibrate_frequency export that was only needed for debug info. Additionally, emit a warning if TSC frequency from calibration differs by more than 10% from the TSC frequency in use, suggesting the use of timing_clock_source = 'system'. Author: Lukas Fittl <[email protected]> Suggested-by: Andres Freund <[email protected]> Reviewed-by: Andres Freund <[email protected]> Reviewed-by: Haibo Yan <[email protected]> Discussion: https://www.postgresql.org/message-id/flat/jr4hk2sxhqcfpb67ftz5g4vw33nm67cgf7go3wwmqsafu5aclq%405m67ukuhyszz#2fdfd95b6a4a74410196999818e16cfc --- doc/src/sgml/ref/pgtesttiming.sgml | 2 + src/bin/pg_test_timing/pg_test_timing.c | 49 +++++++++++++++----- src/common/instr_time.c | 60 +++++++++++++++++++++++-- src/include/port/pg_cpu.h | 2 +- src/include/portability/instr_time.h | 11 ++++- src/port/pg_cpu_x86.c | 28 ++++++++++-- src/tools/pgindent/typedefs.list | 1 + 7 files changed, 134 insertions(+), 19 deletions(-) diff --git a/doc/src/sgml/ref/pgtesttiming.sgml b/doc/src/sgml/ref/pgtesttiming.sgml index 75fcc58d799..bbb511ae94a 100644 --- a/doc/src/sgml/ref/pgtesttiming.sgml +++ b/doc/src/sgml/ref/pgtesttiming.sgml @@ -283,8 +283,10 @@ Observed timing durations up to 99.9900%: ... 61594291 0.0000 100.0000 1 +TSC frequency source: x86, cpuid 0x15 TSC frequency in use: 2449228 kHz TSC frequency from calibration: 2448603 kHz + TSC clock source will be used by default, unless timing_clock_source is set to 'system'. ]]></screen> </para> diff --git a/src/bin/pg_test_timing/pg_test_timing.c b/src/bin/pg_test_timing/pg_test_timing.c index 2afb0e6a410..a31746a256f 100644 --- a/src/bin/pg_test_timing/pg_test_timing.c +++ b/src/bin/pg_test_timing/pg_test_timing.c @@ -7,6 +7,7 @@ #include "postgres_fe.h" #include <limits.h> +#include <math.h> #include "getopt_long.h" #include "port/pg_bitutils.h" @@ -184,7 +185,7 @@ static void test_tsc_timing(void) { uint64 loop_count; - uint32 calibrated_freq; + const TscClockSourceInfo *info; printf("\n"); loop_count = test_timing(test_duration, TIMING_CLOCK_SOURCE_TSC, false); @@ -197,23 +198,51 @@ test_tsc_timing(void) 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); + /* + * Report TSC information regardless of whether it was usable, makes + * debugging a lot easier. + */ + info = pg_timing_tsc_clock_source_info(); + if (info->frequency_source[0] != '\0') + printf(_("TSC frequency source: %s\n"), info->frequency_source); + printf(_("TSC frequency in use: %d kHz\n"), info->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")); + if (info->calibrated_frequency_khz > 0) + { + double diff_pct; + printf(_("TSC frequency from calibration: %d kHz\n"), info->calibrated_frequency_khz); + + diff_pct = fabs((double) info->calibrated_frequency_khz - info->frequency_khz) / + info->frequency_khz * 100.0; + + if (diff_pct > 10.0) + { + printf(_("WARNING: Calibrated TSC frequency differs by %.1f%% from the TSC frequency in use\n"), + diff_pct); + printf(_("HINT: Consider setting timing_clock_source to 'system'. Report bugs to <%s>.\n"), PACKAGE_BUGREPORT); + exit(1); + } + } + else + printf(_("TSC calibration did not converge\n")); + + /* + * Report whether TSC was usable and, if so, whether it will be used + * automatically. + */ + if (loop_count > 0) + { 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")); + printf(_("\nTSC 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")); + printf(_("\nTSC 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")); + printf(_("\nTSC clock source is not usable. Likely unable to determine TSC frequency. Are you running in an unsupported virtualized environment?\n")); } #endif diff --git a/src/common/instr_time.c b/src/common/instr_time.c index fc6e1852c30..6af7693e210 100644 --- a/src/common/instr_time.c +++ b/src/common/instr_time.c @@ -70,6 +70,8 @@ static void set_ticks_per_ns(void); static void set_ticks_per_ns_system(void); #if PG_INSTR_TSC_CLOCK +static TscClockSourceInfo tsc_info = {.calibrated_frequency_khz = -1}; + static bool tsc_use_by_default(void); static void set_ticks_per_ns_for_tsc(void); #endif @@ -166,6 +168,7 @@ set_ticks_per_ns_system(void) #if PG_INSTR_TSC_CLOCK static void tsc_detect_frequency(void); +static uint32 pg_tsc_calibrate_frequency(void); /* * Initialize the TSC clock source by determining its usability and frequency. @@ -202,21 +205,50 @@ static void tsc_detect_frequency(void) { timing_tsc_frequency_khz = 0; + tsc_info.frequency_khz = 0; + tsc_info.frequency_source[0] = '\0'; + + strlcat(tsc_info.frequency_source, "x86", + sizeof(tsc_info.frequency_source)); /* We require RDTSCP support and an invariant TSC, bail if not available */ - if (!x86_feature_available(PG_RDTSCP) || !x86_feature_available(PG_TSC_INVARIANT)) + if (!x86_feature_available(PG_RDTSCP)) + { + strlcat(tsc_info.frequency_source, ", no rdtscp", + sizeof(tsc_info.frequency_source)); return; + } + + if (!x86_feature_available(PG_TSC_INVARIANT)) + { + strlcat(tsc_info.frequency_source, ", not invariant", + sizeof(tsc_info.frequency_source)); + return; + } /* Determine speed at which the TSC advances */ - timing_tsc_frequency_khz = x86_tsc_frequency_khz(); + timing_tsc_frequency_khz = x86_tsc_frequency_khz(tsc_info.frequency_source, + sizeof(tsc_info.frequency_source)); if (timing_tsc_frequency_khz > 0) + { + tsc_info.frequency_khz = timing_tsc_frequency_khz; return; + } /* * CPUID did not give us the TSC frequency. We can instead measure the * frequency by comparing ticks against walltime in a calibration loop. */ - timing_tsc_frequency_khz = pg_tsc_calibrate_frequency(); + if (tsc_info.calibrated_frequency_khz < 0) + tsc_info.calibrated_frequency_khz = pg_tsc_calibrate_frequency(); + + timing_tsc_frequency_khz = tsc_info.calibrated_frequency_khz; + if (timing_tsc_frequency_khz > 0) + { + strlcat(tsc_info.frequency_source, ", calibration", + sizeof(tsc_info.frequency_source)); + tsc_info.frequency_khz = timing_tsc_frequency_khz; + } } /* @@ -282,7 +314,7 @@ tsc_use_by_default(void) #define TSC_CALIBRATION_ITERATIONS 1000000 #define TSC_CALIBRATION_SKIPS 100 #define TSC_CALIBRATION_STABLE_CYCLES 10 -uint32 +static uint32 pg_tsc_calibrate_frequency(void) { instr_time initial_wall; @@ -369,4 +401,24 @@ pg_tsc_calibrate_frequency(void) return (uint32) freq_khz; } +/* + * Returns TSC clock source information for diagnostic purposes. + * + * On first call, may run the TSC calibration loop (if not already done during + * frequency detection) which can take up to TSC_CALIBRATION_MAX_NS. + * Subsequent calls return cached results. + * + * Note: This won't return the right info in EXEC_BACKEND builds if this were + * used in the backend (which it currently is not), as tsc_info is not copied + * using read_backend_variables - only the TSC frequency is. + */ +const TscClockSourceInfo * +pg_timing_tsc_clock_source_info(void) +{ + if (tsc_info.frequency_khz > 0 && tsc_info.calibrated_frequency_khz < 0) + tsc_info.calibrated_frequency_khz = pg_tsc_calibrate_frequency(); + + return &tsc_info; +} + #endif /* PG_INSTR_TSC_CLOCK */ diff --git a/src/include/port/pg_cpu.h b/src/include/port/pg_cpu.h index a5d42f1b68d..db4cd62f7ef 100644 --- a/src/include/port/pg_cpu.h +++ b/src/include/port/pg_cpu.h @@ -56,7 +56,7 @@ x86_feature_available(X86FeatureId feature) return X86Features[feature]; } -extern uint32 x86_tsc_frequency_khz(void); +extern uint32 x86_tsc_frequency_khz(char *source, size_t source_len); #endif /* defined(USE_SSE2) || defined(__i386__) */ diff --git a/src/include/portability/instr_time.h b/src/include/portability/instr_time.h index 92558e234ac..7cd4f38d827 100644 --- a/src/include/portability/instr_time.h +++ b/src/include/portability/instr_time.h @@ -165,10 +165,19 @@ extern PGDLLIMPORT int32 timing_tsc_frequency_khz; extern void pg_initialize_timing_tsc(void); -extern uint32 pg_tsc_calibrate_frequency(void); +typedef struct TscClockSourceInfo +{ + int32 frequency_khz; /* from CPUID or calibration */ + int32 calibrated_frequency_khz; /* from calibration */ + char frequency_source[128]; /* describes how frequency was + * determined */ +} TscClockSourceInfo; + +extern const TscClockSourceInfo *pg_timing_tsc_clock_source_info(void); #endif /* PG_INSTR_TSC_CLOCK */ + /* * Returns the current timing clock source effectively in use, resolving * TIMING_CLOCK_SOURCE_AUTO to either TIMING_CLOCK_SOURCE_SYSTEM or diff --git a/src/port/pg_cpu_x86.c b/src/port/pg_cpu_x86.c index 150b4a1d574..513e9a6b706 100644 --- a/src/port/pg_cpu_x86.c +++ b/src/port/pg_cpu_x86.c @@ -13,7 +13,11 @@ *------------------------------------------------------------------------- */ -#include "c.h" +#ifndef FRONTEND +#include "postgres.h" +#else +#include "postgres_fe.h" +#endif #if defined(USE_SSE2) || defined(__i386__) @@ -161,7 +165,7 @@ static uint32 x86_hypervisor_tsc_frequency_khz(void); * 0 indicates the frequency information was not accessible via CPUID. */ uint32 -x86_tsc_frequency_khz(void) +x86_tsc_frequency_khz(char *source, size_t source_len) { unsigned int reg[4] = {0}; @@ -174,7 +178,17 @@ x86_tsc_frequency_khz(void) * to be wildly incorrect when virtualized. */ if (x86_feature_available(PG_HYPERVISOR)) - return x86_hypervisor_tsc_frequency_khz(); + { + uint32 freq = x86_hypervisor_tsc_frequency_khz(); + + if (source) + { + strlcat(source, ", hypervisor", source_len); + if (freq > 0) + strlcat(source, ", cpuid 0x40000010", source_len); + } + return freq; + } /* * On modern Intel CPUs, the TSC is implemented by invariant timekeeping @@ -207,6 +221,9 @@ x86_tsc_frequency_khz(void) if (reg[EAX] == 0 || reg[EBX] == 0) return 0; + if (source) + strlcat(source, ", cpuid 0x15", source_len); + return reg[ECX] / 1000 * reg[EBX] / reg[EAX]; } @@ -217,7 +234,12 @@ x86_tsc_frequency_khz(void) */ pg_cpuid(0x16, reg); if (reg[EAX] > 0) + { + if (source) + strlcat(source, ", cpuid 0x16", source_len); + return reg[EAX] * 1000; + } return 0; } diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list index ea95e7984bc..2137f1e0cfe 100644 --- a/src/tools/pgindent/typedefs.list +++ b/src/tools/pgindent/typedefs.list @@ -3090,6 +3090,7 @@ TParserStateActionItem TQueueDestReceiver TRGM TSAnyCacheEntry +TscClockSourceInfo TSConfigCacheEntry TSConfigInfo TSDictInfo -- 2.47.1
