From df0341fd3126fab496c73354dae0e52ba6acb395 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Sun, 26 Nov 2023 09:59:05 +1300 Subject: [PATCH v2 1/8] Optimize pg_readv/pg_pwritev for single vector. For some systems that have preadv and pwritev (almost all Unixes), it is known to be slightly faster to call plain old pread and pwrite if you have only one vector, because the kernel avoids extra work following pointers, copying data in, and possibly allocating space. It is debatable where we should do that, but since we already have to use pg_ wrappers for other reasons, that suggests the idea of doing it in there. Avoid adding extra function call overheads by making it static inline, which might also allow the compiler to avoid the branch in some cases where it can see iovcnt's value. For systems that don't have preadv and pwritev (currently: Windows and [closed] Solaris), we might as well pull the replacement functions up into the static inline functions too. Suggested-by: Heikki Linnakangas Discussion: https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@mail.gmail.com --- configure | 23 ----------- configure.ac | 7 +--- src/include/port/pg_iovec.h | 76 +++++++++++++++++++++++++++++++++---- src/port/meson.build | 2 - src/port/preadv.c | 43 --------------------- src/port/pwritev.c | 43 --------------------- src/tools/msvc/Mkvcbuild.pm | 2 +- 7 files changed, 72 insertions(+), 124 deletions(-) delete mode 100644 src/port/preadv.c delete mode 100644 src/port/pwritev.c diff --git a/configure b/configure index c064115038..617da20553 100755 --- a/configure +++ b/configure @@ -16056,9 +16056,6 @@ cat >>confdefs.h <<_ACEOF #define HAVE_DECL_STRNLEN $ac_have_decl _ACEOF - -# We can't use AC_REPLACE_FUNCS to replace these functions, because it -# won't handle deployment target restrictions on macOS ac_fn_c_check_decl "$LINENO" "preadv" "ac_cv_have_decl_preadv" "#include " if test "x$ac_cv_have_decl_preadv" = xyes; then : @@ -16070,16 +16067,6 @@ fi cat >>confdefs.h <<_ACEOF #define HAVE_DECL_PREADV $ac_have_decl _ACEOF -if test $ac_have_decl = 1; then : - -else - case " $LIBOBJS " in - *" preadv.$ac_objext "* ) ;; - *) LIBOBJS="$LIBOBJS preadv.$ac_objext" - ;; -esac - -fi ac_fn_c_check_decl "$LINENO" "pwritev" "ac_cv_have_decl_pwritev" "#include " @@ -16092,16 +16079,6 @@ fi cat >>confdefs.h <<_ACEOF #define HAVE_DECL_PWRITEV $ac_have_decl _ACEOF -if test $ac_have_decl = 1; then : - -else - case " $LIBOBJS " in - *" pwritev.$ac_objext "* ) ;; - *) LIBOBJS="$LIBOBJS pwritev.$ac_objext" - ;; -esac - -fi # This is probably only present on macOS, but may as well check always diff --git a/configure.ac b/configure.ac index f220b379b3..547bfdb514 100644 --- a/configure.ac +++ b/configure.ac @@ -1815,11 +1815,8 @@ AC_CHECK_DECLS(posix_fadvise, [], [], [#include ]) AC_CHECK_DECLS(fdatasync, [], [], [#include ]) AC_CHECK_DECLS([strlcat, strlcpy, strnlen]) - -# We can't use AC_REPLACE_FUNCS to replace these functions, because it -# won't handle deployment target restrictions on macOS -AC_CHECK_DECLS([preadv], [], [AC_LIBOBJ(preadv)], [#include ]) -AC_CHECK_DECLS([pwritev], [], [AC_LIBOBJ(pwritev)], [#include ]) +AC_CHECK_DECLS([preadv], [], [], [#include ]) +AC_CHECK_DECLS([pwritev], [], [], [#include ]) # This is probably only present on macOS, but may as well check always AC_CHECK_DECLS(F_FULLFSYNC, [], [], [#include ]) diff --git a/src/include/port/pg_iovec.h b/src/include/port/pg_iovec.h index 689799c425..0637d6acab 100644 --- a/src/include/port/pg_iovec.h +++ b/src/include/port/pg_iovec.h @@ -17,6 +17,7 @@ #include #include +#include #else @@ -36,20 +37,81 @@ struct iovec #define PG_IOV_MAX Min(IOV_MAX, 32) /* - * Note that pg_preadv and pg_pwritev have a pg_ prefix as a warning that the - * Windows implementations have the side-effect of changing the file position. + * Like preadv(), but with a prefix to remind us of a side-effect: on Windows + * this changes the current file position. */ - +static inline ssize_t +pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset) +{ #if HAVE_DECL_PREADV -#define pg_preadv preadv + /* + * Avoid a small amount of argument copying overhead in the kernel if + * there is only one iovec. + */ + if (iovcnt == 1) + return pread(fd, iov[0].iov_base, iov[0].iov_len, offset); + else + return preadv(fd, iov, iovcnt, offset); #else -extern ssize_t pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset); + ssize_t sum = 0; + ssize_t part; + + for (int i = 0; i < iovcnt; ++i) + { + part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset); + if (part < 0) + { + if (i == 0) + return -1; + else + return sum; + } + sum += part; + offset += part; + if (part < iov[i].iov_len) + return sum; + } + return sum; #endif +} +/* + * Like pwritev(), but with a prefix to remind us of a side-effect: on Windows + * this changes the current file position. + */ +static inline ssize_t +pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset) +{ #if HAVE_DECL_PWRITEV -#define pg_pwritev pwritev + /* + * Avoid a small amount of argument copying overhead in the kernel if + * there is only one iovec. + */ + if (iovcnt == 1) + return pwrite(fd, iov[0].iov_base, iov[0].iov_len, offset); + else + return pwritev(fd, iov, iovcnt, offset); #else -extern ssize_t pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset); + ssize_t sum = 0; + ssize_t part; + + for (int i = 0; i < iovcnt; ++i) + { + part = pg_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset); + if (part < 0) + { + if (i == 0) + return -1; + else + return sum; + } + sum += part; + offset += part; + if (part < iov[i].iov_len) + return sum; + } + return sum; #endif +} #endif /* PG_IOVEC_H */ diff --git a/src/port/meson.build b/src/port/meson.build index a0d0a9583a..576a48b48c 100644 --- a/src/port/meson.build +++ b/src/port/meson.build @@ -66,8 +66,6 @@ replace_funcs_neg = [ ['getpeereid'], ['inet_aton'], ['mkdtemp'], - ['preadv', 'HAVE_DECL_PREADV'], - ['pwritev', 'HAVE_DECL_PWRITEV'], ['strlcat'], ['strlcpy'], ['strnlen'], diff --git a/src/port/preadv.c b/src/port/preadv.c deleted file mode 100644 index e762283e67..0000000000 --- a/src/port/preadv.c +++ /dev/null @@ -1,43 +0,0 @@ -/*------------------------------------------------------------------------- - * - * preadv.c - * Implementation of preadv(2) for platforms that lack one. - * - * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group - * - * IDENTIFICATION - * src/port/preadv.c - * - *------------------------------------------------------------------------- - */ - - -#include "c.h" - -#include - -#include "port/pg_iovec.h" - -ssize_t -pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset) -{ - ssize_t sum = 0; - ssize_t part; - - for (int i = 0; i < iovcnt; ++i) - { - part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset); - if (part < 0) - { - if (i == 0) - return -1; - else - return sum; - } - sum += part; - offset += part; - if (part < iov[i].iov_len) - return sum; - } - return sum; -} diff --git a/src/port/pwritev.c b/src/port/pwritev.c deleted file mode 100644 index 519de45037..0000000000 --- a/src/port/pwritev.c +++ /dev/null @@ -1,43 +0,0 @@ -/*------------------------------------------------------------------------- - * - * pwritev.c - * Implementation of pwritev(2) for platforms that lack one. - * - * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group - * - * IDENTIFICATION - * src/port/pwritev.c - * - *------------------------------------------------------------------------- - */ - - -#include "c.h" - -#include - -#include "port/pg_iovec.h" - -ssize_t -pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset) -{ - ssize_t sum = 0; - ssize_t part; - - for (int i = 0; i < iovcnt; ++i) - { - part = pg_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset); - if (part < 0) - { - if (i == 0) - return -1; - else - return sum; - } - sum += part; - offset += part; - if (part < iov[i].iov_len) - return sum; - } - return sum; -} diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm index 84f648c174..d26d1a84e8 100644 --- a/src/tools/msvc/Mkvcbuild.pm +++ b/src/tools/msvc/Mkvcbuild.pm @@ -104,7 +104,7 @@ sub mkvcbuild inet_net_ntop.c kill.c open.c snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c dirent.c getopt.c getopt_long.c - preadv.c pwritev.c pg_bitutils.c + pg_bitutils.c pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c pqsignal.c mkdtemp.c qsort.c qsort_arg.c bsearch_arg.c quotes.c system.c strerror.c tar.c -- 2.42.1