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Use mutex hint bit in PPC LWARX instructions, where possible.

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The hint bit makes for a small but measurable performance improvement
in access to contended spinlocks.

On the other hand, some PPC chips give an illegal-instruction failure.
There doesn't seem to be a completely bulletproof way to tell whether the
hint bit will cause an illegal-instruction failure other than by trying
it; but most if not all 64-bit PPC machines should accept it, so follow
the Linux kernel's lead and assume it's okay to use it in 64-bit builds.
Of course we must also check whether the assembler accepts the command,
since even with a recent CPU the toolchain could be old.

Patch by Manabu Ori, significantly modified by me.
This commit is contained in:
Tom Lane
2012-01-01 22:39:59 -05:00
parent 6b6137e4ef
commit 5cfa8dd300
5 changed files with 104 additions and 3 deletions
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62
configure vendored
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@ -1635,7 +1635,7 @@ Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
This configure script is free software; the Free Software Foundation
gives unlimited permission to copy, distribute and modify it.
Copyright (c) 1996-2011, PostgreSQL Global Development Group
Copyright (c) 1996-2012, PostgreSQL Global Development Group
_ACEOF
exit
fi
@ -18207,6 +18207,66 @@ rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
conftest$ac_exeext conftest.$ac_ext
fi
# On PPC, check if assembler supports LWARX instruction's mutex hint bit
case $host_cpu in
ppc*|powerpc*)
{ $as_echo "$as_me:$LINENO: checking whether assembler supports lwarx hint bit" >&5
$as_echo_n "checking whether assembler supports lwarx hint bit... " >&6; }
cat >conftest.$ac_ext <<_ACEOF
/* confdefs.h. */
_ACEOF
cat confdefs.h >>conftest.$ac_ext
cat >>conftest.$ac_ext <<_ACEOF
/* end confdefs.h. */
int
main ()
{
int a = 0; int *p = &a; int r;
__asm__ __volatile__ (" lwarx %0,0,%1,1\n" : "=&r"(r) : "r"(p));
;
return 0;
}
_ACEOF
rm -f conftest.$ac_objext
if { (ac_try="$ac_compile"
case "(($ac_try" in
*\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
*) ac_try_echo=$ac_try;;
esac
eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
$as_echo "$ac_try_echo") >&5
(eval "$ac_compile") 2>conftest.er1
ac_status=$?
grep -v '^ *+' conftest.er1 >conftest.err
rm -f conftest.er1
cat conftest.err >&5
$as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
(exit $ac_status); } && {
test -z "$ac_c_werror_flag" ||
test ! -s conftest.err
} && test -s conftest.$ac_objext; then
pgac_cv_have_ppc_mutex_hint=yes
else
$as_echo "$as_me: failed program was:" >&5
sed 's/^/| /' conftest.$ac_ext >&5
pgac_cv_have_ppc_mutex_hint=no
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
{ $as_echo "$as_me:$LINENO: result: $pgac_cv_have_ppc_mutex_hint" >&5
$as_echo "$pgac_cv_have_ppc_mutex_hint" >&6; }
if test x"$pgac_cv_have_ppc_mutex_hint" = xyes ; then
cat >>confdefs.h <<\_ACEOF
#define HAVE_PPC_LWARX_MUTEX_HINT 1
_ACEOF
fi
;;
esac
# Check largefile support. You might think this is a system service not a
# compiler characteristic, but you'd be wrong. We must check this before
# probing existence of related functions such as fseeko, since the largefile