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Commit15c9ac3

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Optimize pg_readv/pg_pwritev single vector case.
For the trivial case of iovcnt == 1, kernels are measurably slower atdealing with the more complex arguments of preadv/pwritev than theequivalent plain old pread/pwrite. The overheads are worth it foriovcnt > 1, but for 1 let's just redirect to the cheaper calls. Whilewe could leave it to callers to worry about that, we already have tohave our own pg_ wrappers for portability reasons so it seemsreasonable to centralize this knowledge there (thanks to Heikki for thissuggestion). Try to avoid function call overheads by making theminlinable, which might also allow the compiler to avoid the branch insome cases. For systems that don't have preadv and pwritev (currently:Windows and [closed] Solaris), we might as well pull the replacementfunctions 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
1 parenta60b8a5 commit15c9ac3

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7 files changed

+74
-120
lines changed

7 files changed

+74
-120
lines changed

‎configure

Lines changed: 1 addition & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -16057,7 +16057,7 @@ cat >>confdefs.h <<_ACEOF
1605716057
_ACEOF
1605816058

1605916059

16060-
# We can't useAC_REPLACE_FUNCS toreplace these functions, because it
16060+
# We can't useAC_CHECK_FUNCS todetect these functions, because it
1606116061
# won't handle deployment target restrictions on macOS
1606216062
ac_fn_c_check_decl "$LINENO" "preadv" "ac_cv_have_decl_preadv" "#include <sys/uio.h>
1606316063
"
@@ -16070,16 +16070,6 @@ fi
1607016070
cat >>confdefs.h <<_ACEOF
1607116071
#define HAVE_DECL_PREADV $ac_have_decl
1607216072
_ACEOF
16073-
if test $ac_have_decl = 1; then :
16074-
16075-
else
16076-
case " $LIBOBJS " in
16077-
*" preadv.$ac_objext "* ) ;;
16078-
*) LIBOBJS="$LIBOBJS preadv.$ac_objext"
16079-
;;
16080-
esac
16081-
16082-
fi
1608316073

1608416074
ac_fn_c_check_decl "$LINENO" "pwritev" "ac_cv_have_decl_pwritev" "#include <sys/uio.h>
1608516075
"
@@ -16092,16 +16082,6 @@ fi
1609216082
cat >>confdefs.h <<_ACEOF
1609316083
#define HAVE_DECL_PWRITEV $ac_have_decl
1609416084
_ACEOF
16095-
if test $ac_have_decl = 1; then :
16096-
16097-
else
16098-
case " $LIBOBJS " in
16099-
*" pwritev.$ac_objext "* ) ;;
16100-
*) LIBOBJS="$LIBOBJS pwritev.$ac_objext"
16101-
;;
16102-
esac
16103-
16104-
fi
1610516085

1610616086

1610716087
# This is probably only present on macOS, but may as well check always

‎configure.ac

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1816,10 +1816,10 @@ AC_CHECK_DECLS(posix_fadvise, [], [], [#include <fcntl.h>])
18161816
AC_CHECK_DECLS(fdatasync,[],[],[#include <unistd.h>])
18171817
AC_CHECK_DECLS([strlcat, strlcpy, strnlen])
18181818

1819-
# We can't useAC_REPLACE_FUNCS toreplace these functions, because it
1819+
# We can't useAC_CHECK_FUNCS todetect these functions, because it
18201820
# won't handle deployment target restrictions on macOS
1821-
AC_CHECK_DECLS([preadv],[],[AC_LIBOBJ(preadv)],[#include <sys/uio.h>])
1822-
AC_CHECK_DECLS([pwritev],[],[AC_LIBOBJ(pwritev)],[#include <sys/uio.h>])
1821+
AC_CHECK_DECLS([preadv],[],[],[#include <sys/uio.h>])
1822+
AC_CHECK_DECLS([pwritev],[],[],[#include <sys/uio.h>])
18231823

18241824
# This is probably only present on macOS, but may as well check always
18251825
AC_CHECK_DECLS(F_FULLFSYNC,[],[],[#include <fcntl.h>])

‎src/include/port/pg_iovec.h

Lines changed: 69 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -17,6 +17,7 @@
1717

1818
#include<limits.h>
1919
#include<sys/uio.h>
20+
#include<unistd.h>
2021

2122
#else
2223

@@ -36,20 +37,81 @@ struct iovec
3637
#definePG_IOV_MAX Min(IOV_MAX, 32)
3738

3839
/*
39-
*Note that pg_preadv and pg_pwritev have a pg_ prefix as awarning that the
40-
*Windows implementations havetheside-effect of changing the file position.
40+
*Like preadv(), but with a prefix to remind us of aside-effect: on Windows
41+
*this changesthecurrent file position.
4142
*/
42-
43+
staticinlinessize_t
44+
pg_preadv(intfd,conststructiovec*iov,intiovcnt,off_toffset)
45+
{
4346
#ifHAVE_DECL_PREADV
44-
#definepg_preadv preadv
47+
/*
48+
* Avoid a small amount of argument copying overhead in the kernel if
49+
* there is only one iovec.
50+
*/
51+
if (iovcnt==1)
52+
returnpread(fd,iov[0].iov_base,iov[0].iov_len,offset);
53+
else
54+
returnpreadv(fd,iov,iovcnt,offset);
4555
#else
46-
externssize_tpg_preadv(intfd,conststructiovec*iov,intiovcnt,off_toffset);
56+
ssize_tsum=0;
57+
ssize_tpart;
58+
59+
for (inti=0;i<iovcnt;++i)
60+
{
61+
part=pg_pread(fd,iov[i].iov_base,iov[i].iov_len,offset);
62+
if (part<0)
63+
{
64+
if (i==0)
65+
return-1;
66+
else
67+
returnsum;
68+
}
69+
sum+=part;
70+
offset+=part;
71+
if (part<iov[i].iov_len)
72+
returnsum;
73+
}
74+
returnsum;
4775
#endif
76+
}
4877

78+
/*
79+
* Like pwritev(), but with a prefix to remind us of a side-effect: on Windows
80+
* this changes the current file position.
81+
*/
82+
staticinlinessize_t
83+
pg_pwritev(intfd,conststructiovec*iov,intiovcnt,off_toffset)
84+
{
4985
#ifHAVE_DECL_PWRITEV
50-
#definepg_pwritev pwritev
86+
/*
87+
* Avoid a small amount of argument copying overhead in the kernel if
88+
* there is only one iovec.
89+
*/
90+
if (iovcnt==1)
91+
returnpwrite(fd,iov[0].iov_base,iov[0].iov_len,offset);
92+
else
93+
returnpwritev(fd,iov,iovcnt,offset);
5194
#else
52-
externssize_tpg_pwritev(intfd,conststructiovec*iov,intiovcnt,off_toffset);
95+
ssize_tsum=0;
96+
ssize_tpart;
97+
98+
for (inti=0;i<iovcnt;++i)
99+
{
100+
part=pg_pwrite(fd,iov[i].iov_base,iov[i].iov_len,offset);
101+
if (part<0)
102+
{
103+
if (i==0)
104+
return-1;
105+
else
106+
returnsum;
107+
}
108+
sum+=part;
109+
offset+=part;
110+
if (part<iov[i].iov_len)
111+
returnsum;
112+
}
113+
returnsum;
53114
#endif
115+
}
54116

55117
#endif/* PG_IOVEC_H */

‎src/port/meson.build

Lines changed: 0 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -66,8 +66,6 @@ replace_funcs_neg = [
6666
['getpeereid'],
6767
['inet_aton'],
6868
['mkdtemp'],
69-
['preadv','HAVE_DECL_PREADV'],
70-
['pwritev','HAVE_DECL_PWRITEV'],
7169
['strlcat'],
7270
['strlcpy'],
7371
['strnlen'],

‎src/port/preadv.c

Lines changed: 0 additions & 43 deletions
This file was deleted.

‎src/port/pwritev.c

Lines changed: 0 additions & 43 deletions
This file was deleted.

‎src/tools/msvc/Mkvcbuild.pm

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -104,7 +104,7 @@ sub mkvcbuild
104104
inet_net_ntop.c kill.c open.c
105105
snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
106106
dirent.c getopt.c getopt_long.c
107-
preadv.c pwritev.cpg_bitutils.c
107+
pg_bitutils.c
108108
pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
109109
pqsignal.c mkdtemp.c qsort.c qsort_arg.c bsearch_arg.c quotes.c system.c
110110
strerror.c tar.c

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