From 3d186bc8be218c609ff9005d88ea6222b3af4445 Mon Sep 17 00:00:00 2001 From: John Naylor Date: Sat, 14 Feb 2026 19:01:34 +0700 Subject: [PATCH v4 4/6] Enable autovectorizing page checksums with AVX2 where available We already rely on autovectorization for computing page checksums, but on x86 we can get about twice the performance by annotating pg_checksum_block() with function target attributes for AVX2, which uses 256-bit registers. Co-authored-by: Matthew Sterrett Co-authored-by: Andrew Kim Reviewed-by: Oleg Tselebrovskiy Discussion: https://postgr.es/m/CA%2BvA85_5GTu%2BHHniSbvvP%2B8k3%3DxZO%3DWE84NPwiKyxztqvpfZ3Q%40mail.gmail.com Discussion: https://postgr.es/m/20250911054220.3784-1-root%40ip-172-31-36-228.ec2.internal --- config/c-compiler.m4 | 26 ++++++++++ configure | 46 ++++++++++++++++++ configure.ac | 9 ++++ meson.build | 30 ++++++++++++ src/backend/storage/page/checksum.c | 44 ++++++++++++++++- src/include/pg_config.h.in | 3 ++ src/include/port/pg_cpu.h | 3 ++ src/include/storage/checksum_block_internal.h | 42 ++++++++++++++++ src/include/storage/checksum_impl.h | 48 ++++++------------- src/port/pg_cpu_x86.c | 6 ++- src/tools/pginclude/headerscheck | 2 + 11 files changed, 224 insertions(+), 35 deletions(-) create mode 100644 src/include/storage/checksum_block_internal.h diff --git a/config/c-compiler.m4 b/config/c-compiler.m4 index 1509dbfa2ab..1f3e31fc2d3 100644 --- a/config/c-compiler.m4 +++ b/config/c-compiler.m4 @@ -613,6 +613,32 @@ fi undefine([Ac_cachevar])dnl ])# PGAC_SSE42_CRC32_INTRINSICS +# PGAC_AVX2_SUPPORT +# --------------------------- +# Check if the compiler supports AVX2 target attribute. +# This is used for optimized checksum calculations with runtime detection. +# +# If AVX2 target attribute is supported, sets pgac_avx2_support. +AC_DEFUN([PGAC_AVX2_SUPPORT], +[define([Ac_cachevar], [AS_TR_SH([pgac_cv_avx2_support])])dnl +AC_CACHE_CHECK([for AVX2 target attribute support], [Ac_cachevar], +[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include + #if defined(__has_attribute) && __has_attribute (target) + __attribute__((target("avx2"))) + static int avx2_test(void) + { + return 0; + } + #endif], + [return avx2_test();])], + [Ac_cachevar=yes], + [Ac_cachevar=no])]) +if test x"$Ac_cachevar" = x"yes"; then + pgac_avx2_support=yes +fi +undefine([Ac_cachevar])dnl +])# PGAC_AVX2_SUPPORT + # PGAC_AVX512_PCLMUL_INTRINSICS # --------------------------- # Check if the compiler supports AVX-512 carryless multiplication diff --git a/configure b/configure index 185703289b4..2d2c6308005 100755 --- a/configure +++ b/configure @@ -17718,6 +17718,52 @@ $as_echo "#define HAVE__CPUIDEX 1" >>confdefs.h fi fi +# Check for AVX2 target and intrinsic support +# +if test x"$host_cpu" = x"x86_64"; then + { $as_echo "$as_me:${as_lineno-$LINENO}: checking for AVX2 target attribute support" >&5 +$as_echo_n "checking for AVX2 target attribute support... " >&6; } +if ${pgac_cv_avx2_support+:} false; then : + $as_echo_n "(cached) " >&6 +else + cat confdefs.h - <<_ACEOF >conftest.$ac_ext +/* end confdefs.h. */ +#include + #if defined(__has_attribute) && __has_attribute (target) + __attribute__((target("avx2"))) + static int avx2_test(void) + { + return 0; + } + #endif +int +main () +{ +return avx2_test(); + ; + return 0; +} +_ACEOF +if ac_fn_c_try_compile "$LINENO"; then : + pgac_cv_avx2_support=yes +else + pgac_cv_avx2_support=no +fi +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext +fi +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_avx2_support" >&5 +$as_echo "$pgac_cv_avx2_support" >&6; } +if test x"$pgac_cv_avx2_support" = x"yes"; then + pgac_avx2_support=yes +fi + + if test x"$pgac_avx2_support" = x"yes"; then + +$as_echo "#define USE_AVX2_WITH_RUNTIME_CHECK 1" >>confdefs.h + + fi +fi + # Check for XSAVE intrinsics # { $as_echo "$as_me:${as_lineno-$LINENO}: checking for _xgetbv" >&5 diff --git a/configure.ac b/configure.ac index 0955b7e4371..0b4c3970b68 100644 --- a/configure.ac +++ b/configure.ac @@ -2122,6 +2122,15 @@ else fi fi +# Check for AVX2 target and intrinsic support +# +if test x"$host_cpu" = x"x86_64"; then + PGAC_AVX2_SUPPORT() + if test x"$pgac_avx2_support" = x"yes"; then + AC_DEFINE(USE_AVX2_WITH_RUNTIME_CHECK, 1, [Define to 1 to use AVX2 instructions with a runtime check.]) + fi +fi + # Check for XSAVE intrinsics # PGAC_XSAVE_INTRINSICS() diff --git a/meson.build b/meson.build index f6d5842d852..feea3658ff3 100644 --- a/meson.build +++ b/meson.build @@ -2377,6 +2377,36 @@ int main(void) endif +############################################################### +# Check for the availability of AVX2 support +############################################################### + +if host_cpu == 'x86_64' + + prog = ''' +#include +#include +#if defined(__has_attribute) && __has_attribute (target) +__attribute__((target("avx2"))) +#endif +static int avx2_test(void) +{ + return 0; +} + +int main(void) +{ + return avx2_test(); +} +''' + + if cc.links(prog, name: 'AVX2 support', args: test_c_args) + cdata.set('USE_AVX2_WITH_RUNTIME_CHECK', 1) + endif + +endif + + ############################################################### # Check for the availability of AVX-512 popcount intrinsics. ############################################################### diff --git a/src/backend/storage/page/checksum.c b/src/backend/storage/page/checksum.c index 8716651c8b5..030c44f7308 100644 --- a/src/backend/storage/page/checksum.c +++ b/src/backend/storage/page/checksum.c @@ -13,10 +13,52 @@ */ #include "postgres.h" +#include "port/pg_cpu.h" #include "storage/checksum.h" /* * The actual code is in storage/checksum_impl.h. This is done so that * external programs can incorporate the checksum code by #include'ing - * that file from the exported Postgres headers. (Compare our CRC code.) + * that file from the exported Postgres headers. (Compare our legacy + * CRC code in pg_crc.h.) + * The PG_CHECKSUM_INTERNAL symbol allows core to use hardware-specific + * coding without affecting external programs. */ +#define PG_CHECKSUM_INTERNAL #include "storage/checksum_impl.h" /* IWYU pragma: keep */ + + +static uint32 +pg_checksum_block_fallback(const PGChecksummablePage *page) +{ +#include "storage/checksum_block_internal.h" +} + +/* + * AVX2-optimized block checksum algorithm. + */ +#ifdef USE_AVX2_WITH_RUNTIME_CHECK +pg_attribute_target("avx2") +static uint32 +pg_checksum_block_avx2(const PGChecksummablePage *page) +{ +#include "storage/checksum_block_internal.h" +} +#endif /* USE_AVX2_WITH_RUNTIME_CHECK */ + +/* + * Choose the best available checksum implementation. + */ +static uint32 +pg_checksum_choose(const PGChecksummablePage *page) +{ + pg_checksum_block = pg_checksum_block_fallback; + +#ifdef USE_AVX2_WITH_RUNTIME_CHECK + if (x86_feature_available(PG_AVX2)) + pg_checksum_block = pg_checksum_block_avx2; +#endif + + return pg_checksum_block(page); +} + +static uint32 (*pg_checksum_block) (const PGChecksummablePage *page) = pg_checksum_choose; diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in index 339268dc8ef..1e43e9b2bc4 100644 --- a/src/include/pg_config.h.in +++ b/src/include/pg_config.h.in @@ -665,6 +665,9 @@ /* Define to 1 to use AVX-512 CRC algorithms with a runtime check. */ #undef USE_AVX512_CRC32C_WITH_RUNTIME_CHECK +/* Define to 1 to use AVX2 instructions with a runtime check. */ +#undef USE_AVX2_WITH_RUNTIME_CHECK + /* Define to 1 to use AVX-512 popcount instructions with a runtime check. */ #undef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK diff --git a/src/include/port/pg_cpu.h b/src/include/port/pg_cpu.h index c9e03d016e9..3c70fd43a23 100644 --- a/src/include/port/pg_cpu.h +++ b/src/include/port/pg_cpu.h @@ -24,6 +24,9 @@ typedef enum X86FeatureId PG_SSE4_2, PG_POPCNT, + /* 256-bit registers */ + PG_AVX2, + /* 512-bit registers */ PG_AVX512_BW, PG_AVX512_VL, diff --git a/src/include/storage/checksum_block_internal.h b/src/include/storage/checksum_block_internal.h new file mode 100644 index 00000000000..b4e6987d6b5 --- /dev/null +++ b/src/include/storage/checksum_block_internal.h @@ -0,0 +1,42 @@ +/*------------------------------------------------------------------------- + * + * checksum_block_internal.h + * Core algorithm for page checksums , semi private to checksum_impl.h + * and checksum.c. + * + * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/include/storage/checksum_block_internal.h + * + *------------------------------------------------------------------------- + */ + +/* there is deliberately not an #ifndef CHECKSUM_BLOCK_INTERNAL_H here */ + +uint32 sums[N_SUMS]; +uint32 result = 0; +uint32 i, + j; + +/* ensure that the size is compatible with the algorithm */ +Assert(sizeof(PGChecksummablePage) == BLCKSZ); + +/* initialize partial checksums to their corresponding offsets */ +memcpy(sums, checksumBaseOffsets, sizeof(checksumBaseOffsets)); + +/* main checksum calculation */ +for (i = 0; i < (uint32) (BLCKSZ / (sizeof(uint32) * N_SUMS)); i++) + for (j = 0; j < N_SUMS; j++) + CHECKSUM_COMP(sums[j], page->data[i][j]); + +/* finally add in two rounds of zeroes for additional mixing */ +for (i = 0; i < 2; i++) + for (j = 0; j < N_SUMS; j++) + CHECKSUM_COMP(sums[j], 0); + +/* xor fold partial checksums together */ +for (i = 0; i < N_SUMS; i++) + result ^= sums[i]; + +return result; diff --git a/src/include/storage/checksum_impl.h b/src/include/storage/checksum_impl.h index 5c2dcbc63e7..8a308e423c3 100644 --- a/src/include/storage/checksum_impl.h +++ b/src/include/storage/checksum_impl.h @@ -73,11 +73,10 @@ * 2e-16 false positive rate within margin of error. * * Vectorization of the algorithm requires 32bit x 32bit -> 32bit integer - * multiplication instruction. As of 2013 the corresponding instruction is - * available on x86 SSE4.1 extensions (pmulld) and ARM NEON (vmul.i32). - * Vectorization requires a compiler to do the vectorization for us. For recent - * GCC versions the flags -msse4.1 -funroll-loops -ftree-vectorize are enough - * to achieve vectorization. + * multiplication instruction. Examples include x86 AVX2 extensions (vpmulld) + * and ARM NEON (vmul.i32). For simplicity we rely on the compiler to do the + * vectorization for us. For GCC and clang the flags -funroll-loops + * -ftree-vectorize are enough to achieve vectorization. * * The optimal amount of parallelism to use depends on CPU specific instruction * latency, SIMD instruction width, throughput and the amount of registers @@ -89,8 +88,9 @@ * * The parallelism number 32 was chosen based on the fact that it is the * largest state that fits into architecturally visible x86 SSE registers while - * leaving some free registers for intermediate values. For future processors - * with 256bit vector registers this will leave some performance on the table. + * leaving some free registers for intermediate values. For processors + * with 256bit vector registers this leaves some performance on the table. + * * When vectorization is not available it might be beneficial to restructure * the computation to calculate a subset of the columns at a time and perform * multiple passes to avoid register spilling. This optimization opportunity @@ -138,6 +138,9 @@ do { \ (checksum) = __tmp * FNV_PRIME ^ (__tmp >> 17); \ } while (0) +/* Provide a static definition for external programs */ +#ifndef PG_CHECKSUM_INTERNAL + /* * Block checksum algorithm. The page must be adequately aligned * (at least on 4-byte boundary). @@ -145,34 +148,13 @@ do { \ static uint32 pg_checksum_block(const PGChecksummablePage *page) { - uint32 sums[N_SUMS]; - uint32 result = 0; - uint32 i, - j; - - /* ensure that the size is compatible with the algorithm */ - Assert(sizeof(PGChecksummablePage) == BLCKSZ); - - /* initialize partial checksums to their corresponding offsets */ - memcpy(sums, checksumBaseOffsets, sizeof(checksumBaseOffsets)); - - /* main checksum calculation */ - for (i = 0; i < (uint32) (BLCKSZ / (sizeof(uint32) * N_SUMS)); i++) - for (j = 0; j < N_SUMS; j++) - CHECKSUM_COMP(sums[j], page->data[i][j]); - - /* finally add in two rounds of zeroes for additional mixing */ - for (i = 0; i < 2; i++) - for (j = 0; j < N_SUMS; j++) - CHECKSUM_COMP(sums[j], 0); - - /* xor fold partial checksums together */ - for (i = 0; i < N_SUMS; i++) - result ^= sums[i]; - - return result; +#include "storage/checksum_block_internal.h" } +#else +static uint32 (*pg_checksum_block) (const PGChecksummablePage *page); +#endif + /* * Compute the checksum for a Postgres page. * diff --git a/src/port/pg_cpu_x86.c b/src/port/pg_cpu_x86.c index 9b462b186b8..a48c39ade98 100644 --- a/src/port/pg_cpu_x86.c +++ b/src/port/pg_cpu_x86.c @@ -74,7 +74,7 @@ set_x86_features(void) { uint32 xcr0_val = 0; - /* second cpuid call on leaf 7 to check extended AVX-512 support */ + /* second cpuid call on leaf 7 to check extended support */ memset(exx, 0, 4 * sizeof(exx[0])); #if defined(HAVE__GET_CPUID_COUNT) __get_cpuid_count(7, 0, &exx[0], &exx[1], &exx[2], &exx[3]); @@ -87,6 +87,10 @@ set_x86_features(void) xcr0_val = _xgetbv(0); #endif + /* Are YMM registers enabled? */ + if (mask_available(xcr0_val, XMM | YMM)) + X86Features[PG_AVX2] = exx[1] >> 5 & 1; + /* Are ZMM registeres enabled? */ if (mask_available(xcr0_val, XMM | YMM | OPMASK | ZMM0_15 | ZMM16_31)) diff --git a/src/tools/pginclude/headerscheck b/src/tools/pginclude/headerscheck index 7a6755991bb..569e749b25a 100755 --- a/src/tools/pginclude/headerscheck +++ b/src/tools/pginclude/headerscheck @@ -154,6 +154,8 @@ do test "$f" = src/include/catalog/syscache_ids.h && continue test "$f" = src/include/catalog/syscache_info.h && continue + test "$f" = src/include/storage/checksum_block_internal.h && continue + # We can't make these Bison output files compilable standalone # without using "%code require", which old Bison versions lack. # parser/gram.h will be included by parser/gramparse.h anyway. -- 2.53.0