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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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18
configure.in
View File

@ -1170,11 +1170,27 @@ if test "$with_krb5" = yes; then
AC_MSG_CHECKING(for krb5_free_unparsed_name)
AC_TRY_LINK([#include <krb5.h>],
[krb5_free_unparsed_name(NULL,NULL);],
[AC_DEFINE(HAVE_KRB5_FREE_UNPARSED_NAME, 1, [Define to 1 if you have krb5_free_unparsed_name])
[AC_DEFINE(HAVE_KRB5_FREE_UNPARSED_NAME, 1, [Define to 1 if you have krb5_free_unparsed_name.])
AC_MSG_RESULT(yes)],
[AC_MSG_RESULT(no)])
fi
# On PPC, check if assembler supports LWARX instruction's mutex hint bit
case $host_cpu in
ppc*|powerpc*)
AC_MSG_CHECKING([whether assembler supports lwarx hint bit])
AC_TRY_COMPILE([],
[int a = 0; int *p = &a; int r;
__asm__ __volatile__ (" lwarx %0,0,%1,1\n" : "=&r"(r) : "r"(p));],
[pgac_cv_have_ppc_mutex_hint=yes],
[pgac_cv_have_ppc_mutex_hint=no])
AC_MSG_RESULT([$pgac_cv_have_ppc_mutex_hint])
if test x"$pgac_cv_have_ppc_mutex_hint" = xyes ; then
AC_DEFINE(HAVE_PPC_LWARX_MUTEX_HINT, 1, [Define to 1 if the assembler supports PPC's LWARX mutex hint bit.])
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