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v4.1.x: Powerpc atomics: Force usage of powerpc assembly. #8708

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Merged
merged 1 commit into from
Mar 29, 2021
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v4.1.x: Powerpc atomics: Force usage of powerpc assembly. #8708

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12 changes: 12 additions & 0 deletions config/opal_config_asm.m4
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Original file line number Diff line number Diff line change
Expand Up @@ -1136,6 +1136,18 @@ AC_DEFUN([OPAL_CONFIG_ASM],[
AC_MSG_ERROR([Could not determine PowerPC word size: $ac_cv_sizeof_long])
fi
OPAL_GCC_INLINE_ASSIGN='"1: li %0,0" : "=&r"(ret)'

# See the following github PR and some performance numbers/discussion:
# https://github.com/open-mpi/ompi/pull/8649
AC_MSG_CHECKING([$opal_cv_asm_arch: Checking if force gcc atomics requested])
if test $force_gcc_atomics_ppc = 0 ; then
AC_MSG_RESULT([no])
opal_cv_asm_builtin="BUILTIN_NO"
else
AC_MSG_RESULT([Yes])
AC_MSG_WARN([$opal_cv_asm_arch: gcc atomics have been known to perform poorly on powerpc.])
fi

;;
# There is no current difference between s390 and s390x
# But use two different defines in case some come later
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7 changes: 7 additions & 0 deletions config/opal_configure_options.m4
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Expand Up @@ -84,6 +84,13 @@ else
WANT_BRANCH_PROBABILITIES=0
fi

AC_ARG_ENABLE([builtin-atomics-for-ppc],[AS_HELP_STRING([--enable-builtin-atomics-for-ppc],
[POWER architectures only: Force use of builtin atomics if available. This could either be gcc builtins or C11 atomics, depending on what is available on your system. Enabling this is known to cause poor performance in atomic operations on Power machines. (default: disabled)])])
if test "x$enable_builtin_atomics_for_ppc" = "xyes" ; then
force_gcc_atomics_ppc=1
else
force_gcc_atomics_ppc=0
fi

#
# Memory debugging
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