From 15c9ac3629936a9bb5010155d3656e913027ccb7 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Wed, 29 Nov 2023 16:44:19 +1300 Subject: [PATCH] Optimize pg_readv/pg_pwritev single vector case. For the trivial case of iovcnt == 1, kernels are measurably slower at dealing with the more complex arguments of preadv/pwritev than the equivalent plain old pread/pwrite. The overheads are worth it for iovcnt > 1, but for 1 let's just redirect to the cheaper calls. While we could leave it to callers to worry about that, we already have to have our own pg_ wrappers for portability reasons so it seems reasonable to centralize this knowledge there (thanks to Heikki for this suggestion). Try to avoid function call overheads by making them inlinable, which might also allow the compiler to avoid the branch in some cases. 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. Reviewed-by: Heikki Linnakangas Discussion: https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@mail.gmail.com --- configure | 22 +--------- configure.ac | 6 +-- src/include/port/pg_iovec.h | 82 ++++++++++++++++++++++++++++++++----- src/port/meson.build | 2 - src/port/preadv.c | 43 ------------------- src/port/pwritev.c | 43 ------------------- src/tools/msvc/Mkvcbuild.pm | 2 +- 7 files changed, 77 insertions(+), 123 deletions(-) delete mode 100644 src/port/preadv.c delete mode 100644 src/port/pwritev.c diff --git a/configure b/configure index bf3ea690db..217704e9ca 100755 --- a/configure +++ b/configure @@ -16057,7 +16057,7 @@ cat >>confdefs.h <<_ACEOF _ACEOF -# We can't use AC_REPLACE_FUNCS to replace these functions, because it +# We can't use AC_CHECK_FUNCS to detect 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 " @@ -16070,16 +16070,6 @@ 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 +16082,6 @@ 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 fed7167e65..e49de9e4f0 100644 --- a/configure.ac +++ b/configure.ac @@ -1816,10 +1816,10 @@ 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 +# We can't use AC_CHECK_FUNCS to detect 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); -#endif + ssize_t sum = 0; + ssize_t part; -#if HAVE_DECL_PWRITEV -#define pg_pwritev pwritev -#else -extern ssize_t pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset); + 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 + /* + * 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 + 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