database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-28 23:42:10 +03:00
Code Activity

Optimize pg_readv/pg_pwritev single vector case.

Browse Source 
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 <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@mail.gmail.com
This commit is contained in:
Thomas Munro
2023-11-29 16:44:19 +13:00
parent a60b8a58f4
commit 15c9ac3629
7 changed files with 77 additions and 123 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
configure vendored
View File

@ -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 <sys/uio.h>
"
@ -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 <sys/uio.h>
"
@ -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