opal/atomic: always use C11 atomics if available

This commit disables the use of both the builtin and hand-written
atomics if proper C11 atomic support is detected. This is the first
step towards requiring the availability of C11 atomics for the C
compiler used to build Open MPI.

Signed-off-by: Nathan Hjelm <[email protected]>

Author: hjelmn

config/opal_config_asm.m4

@@ -25,6 +25,50 @@ dnl $HEADER$
 dnl
 
 
+AC_DEFUN([OPAL_CHECK_C11_CSWAP_INT128], [
+
+  OPAL_VAR_SCOPE_PUSH([c11_compare_and_swap_128_result c11_CFLAGS_save])
+
+  AC_ARG_ENABLE([cross-cmpset128],[AC_HELP_STRING([--enable-cross-cmpset128],
+                [enable the use of the C11 atomic compare-and-swap 128 when cross compiling])])
+
+  c11_compare_and_swap_128_result=0
+
+  # This test specifically DOES NOT use -latomic because we do not want a lock-based atomic
+  for flag in "" "-mcx16" ; do
+      c11_CFLAGS_save=$CFLAGS
+      if test "x$flag" != "x" ; then
+	  AC_MSG_CHECKING([for compiler support for C11 atomic compare-and-swap on 128-bit values with flag $flag])
+	  CFLAGS="$CFLAGS $flag"
+      else
+	  AC_MSG_CHECKING([for compiler support for C11 atomic compare-and-swap on 128-bit values])
+      fi
+
+      if test ! "$enable_cross_cmpset128" = "yes" ; then
+	  AC_RUN_IFELSE([AC_LANG_PROGRAM([#include <stdatomic.h>], [__int128 x = 0; atomic_compare_exchange_strong (&x, &(__int128){0}, 1); return !atomic_is_lock_free(&x);])],
+	                [AC_MSG_RESULT([yes]); c11_compare_and_swap_128_result=1; break],
+                        [AC_MSG_RESULT([no])], [AC_MSG_RESULT([no (cross compiling)])])
+      else
+	 AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <stdatomic.h>], [__int128 x = 0; atomic_compare_exchange_strong (&x, &(__int128){0}, 1);])],
+	                [AC_MSG_RESULT([yes]); c11_compare_and_swap_128_result=1; break],
+		        [AC_MSG_RESULT([no])])
+      fi
+
+      CFLAGS=$c11_CFLAGS_save
+  done
+
+  AC_DEFINE_UNQUOTED([OPAL_HAVE_C11_CSWAP_INT128], [$c11_compare_and_swap_128_result],
+	[Whether the compiler support C11 atomic compare and swap supports 128-bit values])
+
+  # For x86_64 systems it is impossible to get cmpxchng16b to be used do to slow reads of atomic variables. In Open MPI
+  # we are careful to read these values in consistent way so use __sync instead.
+  if test $c11_compare_and_swap_128_result = 0 ; then
+      OPAL_CHECK_SYNC_BUILTIN_CSWAP_INT128
+  fi
+
+  OPAL_VAR_SCOPE_POP
+])
+
 AC_DEFUN([OPAL_CHECK_SYNC_BUILTIN_CSWAP_INT128], [
 
   OPAL_VAR_SCOPE_PUSH([sync_bool_compare_and_swap_128_result CFLAGS_save])
@@ -911,17 +955,27 @@ AC_DEFUN([OPAL_CONFIG_ASM],[
     AC_REQUIRE([OPAL_SETUP_CC])
     AC_REQUIRE([AM_PROG_AS])
 
+    AC_ARG_ENABLE([c11-atomics],[AC_HELP_STRING([--enable-c11-atomics],
+                  [Enable use of C11 atomics if available (default: enabled)])])
+
     AC_ARG_ENABLE([builtin-atomics],
       [AC_HELP_STRING([--enable-builtin-atomics],
-         [Enable use of __sync builtin atomics (default: enabled)])])
-
-    opal_cv_asm_builtin="BUILTIN_NO"
-    AS_IF([test "$opal_cv_asm_builtin" = "BUILTIN_NO" && test "$enable_builtin_atomics" != "no"],
-          [OPAL_CHECK_GCC_ATOMIC_BUILTINS([opal_cv_asm_builtin="BUILTIN_GCC"], [])])
-    AS_IF([test "$opal_cv_asm_builtin" = "BUILTIN_NO" && test "$enable_builtin_atomics" != "no"],
-          [OPAL_CHECK_SYNC_BUILTINS([opal_cv_asm_builtin="BUILTIN_SYNC"], [])])
-    AS_IF([test "$opal_cv_asm_builtin" = "BUILTIN_NO" && test "$enable_builtin_atomics" = "yes"],
-          [AC_MSG_ERROR([__sync builtin atomics requested but not found.])])
+         [Enable use of __sync builtin atomics (default: disabled)])])
+
+    OPAL_CHECK_C11_CSWAP_INT128
+
+    if test "x$enable_c11_atomics" != "no" && test "$opal_cv_c11_supported" = "yes" ; then
+        opal_cv_asm_builtin="BUILTIN_C11"
+        OPAL_CHECK_C11_CSWAP_INT128
+    else
+        opal_cv_asm_builtin="BUILTIN_NO"
+        AS_IF([test "$opal_cv_asm_builtin" = "BUILTIN_NO" && test "$enable_builtin_atomics" = "yes"],
+              [OPAL_CHECK_GCC_ATOMIC_BUILTINS([opal_cv_asm_builtin="BUILTIN_GCC"], [])])
+        AS_IF([test "$opal_cv_asm_builtin" = "BUILTIN_NO" && test "$enable_builtin_atomics" = "yes"],
+              [OPAL_CHECK_SYNC_BUILTINS([opal_cv_asm_builtin="BUILTIN_SYNC"], [])])
+        AS_IF([test "$opal_cv_asm_builtin" = "BUILTIN_NO" && test "$enable_builtin_atomics" = "yes"],
+              [AC_MSG_ERROR([__sync builtin atomics requested but not found.])])
+    fi
 
         OPAL_CHECK_ASM_PROC
         OPAL_CHECK_ASM_TEXT

opal/class/opal_fifo.h

@@ -155,11 +155,9 @@ static inline opal_list_item_t *opal_fifo_pop_atomic (opal_fifo_t *fifo)
              * update the head */
 
             /* wait for next pointer to be updated by push */
-            while (ghost == item->opal_list_next) {
+            do {
                 opal_atomic_rmb ();
-            }
-
-            opal_atomic_rmb ();
+            } while (ghost == item->opal_list_next);
 
             /* update the head with the real next value. note that no other thread
              * will be attempting to update the head until after it has been updated

opal/class/opal_object.c

@@ -55,7 +55,7 @@ int opal_class_init_epoch = 1;
 /*
  * Local variables
  */
-static opal_atomic_lock_t class_lock = { { OPAL_ATOMIC_LOCK_UNLOCKED } };
+static opal_atomic_lock_t class_lock = OPAL_ATOMIC_LOCK_INIT;
 static void** classes = NULL;
 static int num_classes = 0;
 static int max_classes = 0;

opal/include/opal/sys/Makefile.am

@@ -11,7 +11,7 @@
 #                         All rights reserved.
 # Copyright (c) 2010      Cisco Systems, Inc.  All rights reserved.
 # Copyright (c) 2011      Sandia National Laboratories. All rights reserved.
-# Copyright (c) 2016      Los Alamos National Security, LLC. All rights
+# Copyright (c) 2016-2018 Los Alamos National Security, LLC. All rights
 #                         reserved.
 # Copyright (c) 2017      Research Organization for Information Science
 #                         and Technology (RIST). All rights reserved.
@@ -27,6 +27,7 @@
 headers += \
 	opal/sys/architecture.h \
 	opal/sys/atomic.h \
+	opal/sys/atomic_stdc.h \
 	opal/sys/atomic_impl.h \
 	opal/sys/timer.h \
         opal/sys/cma.h

opal/include/opal/sys/architecture.h

@@ -47,6 +47,7 @@
 #define OPAL_BUILTIN_SYNC   0200
 #define OPAL_BUILTIN_GCC    0202
 #define OPAL_BUILTIN_NO     0203
+#define OPAL_BUILTIN_C11    0204
 
 /* Formats */
 #define OPAL_DEFAULT        1000  /* standard for given architecture */

opal/include/opal/sys/atomic.h

@@ -58,6 +58,12 @@
 #include "opal/sys/architecture.h"
 #include "opal_stdatomic.h"
 
+#if OPAL_ASSEMBLY_BUILTIN == OPAL_BUILTIN_C11
+
+#include "atomic_stdc.h"
+
+#else /* !OPAL_C_HAVE__ATOMIC */
+
 /* do some quick #define cleanup in cases where we are doing
    testing... */
 #ifdef OPAL_DISABLE_INLINE_ASM
@@ -147,6 +153,8 @@ enum {
     OPAL_ATOMIC_LOCK_LOCKED = 1
 };
 
+#define OPAL_ATOMIC_LOCK_INIT {.u = {.lock = OPAL_ATOMIC_LOCK_UNLOCKED}}
+
 /**********************************************************************
  *
  * Load the appropriate architecture files and set some reasonable
@@ -643,6 +651,8 @@ static inline intptr_t opal_atomic_fetch_sub_ptr( opal_atomic_intptr_t* addr, vo
  */
 #include "opal/sys/atomic_impl.h"
 
+#endif /* !OPAL_C_HAVE__ATOMIC */
+
 END_C_DECLS
 
 #endif /* OPAL_SYS_ATOMIC_H */