Add elision tunables

This patch adds several new tunables to control the behavior of
elision on supported platforms[1].   Since elision now depends
on tunables, we should always *compile* with elision enabled,
and leave the code disabled, but available for runtime
selection.  This gives us *much* better compile-time testing of
the existing code to avoid bit-rot[2].

Tested on ppc, ppc64, ppc64le, s390x and x86_64.

[1] This part of the patch was initially proposed by
Paul Murphy but was "staled" because the framework have changed
since the patch was originally proposed:

https://patchwork.sourceware.org/patch/10342/

[2] This part of the patch was inititally proposed as a RFC by
Carlos O'Donnell.  Make sense to me integrate this on the patch:

https://sourceware.org/ml/libc-alpha/2017-05/msg00335.html

	* elf/dl-tunables.list: Add elision parameters.
	* manual/tunables.texi: Add entries about elision tunable.
	* sysdeps/unix/sysv/linux/powerpc/elision-conf.c:
	Add callback functions to dynamically enable/disable elision.
	Add multiple callbacks functions to set elision parameters.
	Deleted __libc_enable_secure check.
	* sysdeps/unix/sysv/linux/s390/elision-conf.c: Likewise.
	* sysdeps/unix/sysv/linux/x86/elision-conf.c: Likewise.
	* configure: Regenerated.
	* configure.ac: Option enable_lock_elision was deleted.
	* config.h.in: ENABLE_LOCK_ELISION flag was deleted.
	* config.make.in: Remove references to enable_lock_elision.
	* manual/install.texi: Elision configure option was removed.
	* INSTALL: Regenerated to remove enable_lock_elision.
	* nptl/Makefile:
	Disable elision so it can verify error case for destroying a mutex.
	* sysdeps/powerpc/nptl/elide.h:
	Cleanup ENABLE_LOCK_ELISION check.
	Deleted macros for the case when ENABLE_LOCK_ELISION was not defined.
	* sysdeps/s390/configure: Regenerated.
	* sysdeps/s390/configure.ac: Remove references to enable_lock_elision..
	* nptl/tst-mutex8.c:
	Deleted all #ifndef ENABLE_LOCK_ELISION from the test.
	* sysdeps/powerpc/powerpc32/sysdep.h:
	Deleted all ENABLE_LOCK_ELISION checks.
	* sysdeps/powerpc/powerpc64/sysdep.h: Likewise.
	* sysdeps/powerpc/sysdep.h: Likewise.
	* sysdeps/s390/nptl/bits/pthreadtypes-arch.h: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/force-elision.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/elision-conf.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/force-elision.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/lowlevellock.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/Makefile: Remove references to
	enable-lock-elision.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>

15 files changed, 209 insertions, 47 deletions

diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
index 1c42814..06986cc 100644
--- a/sysdeps/powerpc/nptl/elide.h
+++ b/sysdeps/powerpc/nptl/elide.h
@@ -19,7 +19,6 @@
 #ifndef ELIDE_PPC_H
 # define ELIDE_PPC_H
 
-#ifdef ENABLE_LOCK_ELISION
 # include <htm.h>
 # include <elision-conf.h>
 
@@ -114,12 +113,4 @@ __elide_unlock (int is_lock_free)
 # define ELIDE_UNLOCK(is_lock_free) \
   __elide_unlock (is_lock_free)
 
-# else
-
-# define ELIDE_LOCK(adapt_count, is_lock_free) 0
-# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) 0
-# define ELIDE_UNLOCK(is_lock_free) 0
-
-#endif /* ENABLE_LOCK_ELISION  */
-
 #endif
diff --git a/sysdeps/powerpc/powerpc32/sysdep.h b/sysdeps/powerpc/powerpc32/sysdep.h
index 965ea43..1d2ff73 100644
--- a/sysdeps/powerpc/powerpc32/sysdep.h
+++ b/sysdeps/powerpc/powerpc32/sysdep.h
@@ -90,7 +90,7 @@ GOT_LABEL:			;					      \
   cfi_endproc;								      \
   ASM_SIZE_DIRECTIVE(name)
 
-#if ! IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
+#if ! IS_IN(rtld)
 # define ABORT_TRANSACTION \
     cmpwi    2,0;		\
     beq      1f;		\
diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h
index ab5f395..bff184e 100644
--- a/sysdeps/powerpc/powerpc64/sysdep.h
+++ b/sysdeps/powerpc/powerpc64/sysdep.h
@@ -263,7 +263,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
   TRACEBACK_MASK(name,mask);	\
   END_2(name)
 
-#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
+#if !IS_IN(rtld)
 # define ABORT_TRANSACTION \
     cmpdi    13,0;		\
     beq      1f;		\
diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h
index f07b959..d1a9bd9 100644
--- a/sysdeps/powerpc/sysdep.h
+++ b/sysdeps/powerpc/sysdep.h
@@ -21,10 +21,8 @@
  */
 #define _SYSDEPS_SYSDEP_H 1
 #include <bits/hwcap.h>
-#ifdef ENABLE_LOCK_ELISION
 #include <tls.h>
 #include <htm.h>
-#endif
 
 #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
 
@@ -176,7 +174,7 @@
    we abort transaction just before syscalls.
 
    [1] Documentation/powerpc/transactional_memory.txt [Syscalls]  */
-#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
+#if !IS_IN(rtld)
 # define ABORT_TRANSACTION \
   ({ 						\
     if (THREAD_GET_TM_CAPABLE ())		\
diff --git a/sysdeps/s390/configure b/sysdeps/s390/configure
index d4a4a3d..74b415f 100644
--- a/sysdeps/s390/configure
+++ b/sysdeps/s390/configure
@@ -35,7 +35,7 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_builtin_tbegin" >&5
 $as_echo "$libc_cv_gcc_builtin_tbegin" >&6; }
 
-if test "$enable_lock_elision" = yes && test "$libc_cv_gcc_builtin_tbegin" = no ; then
+if test "$libc_cv_gcc_builtin_tbegin" = no ; then
    critic_missing="$critic_missing The used GCC has no support for __builtin_tbegin, which is needed for lock-elision on target S390."
 fi
 
diff --git a/sysdeps/s390/configure.ac b/sysdeps/s390/configure.ac
index 7d0b5ce..1cdb021 100644
--- a/sysdeps/s390/configure.ac
+++ b/sysdeps/s390/configure.ac
@@ -26,7 +26,7 @@ else
 fi
 rm -f conftest* ])
 
-if test "$enable_lock_elision" = yes && test "$libc_cv_gcc_builtin_tbegin" = no ; then
+if test "$libc_cv_gcc_builtin_tbegin" = no ; then
    critic_missing="$critic_missing The used GCC has no support for __builtin_tbegin, which is needed for lock-elision on target S390."
 fi
 
diff --git a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
index 1ae2773..fd15931 100644
--- a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
+++ b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
@@ -40,11 +40,7 @@
 /* Definitions for internal mutex struct.  */
 #define __PTHREAD_COMPAT_PADDING_MID
 #define __PTHREAD_COMPAT_PADDING_END
-#ifdef ENABLE_LOCK_ELISION
 #define __PTHREAD_MUTEX_LOCK_ELISION    1
-#else
-#define __PTHREAD_MUTEX_LOCK_ELISION	0
-#endif
 #define __PTHREAD_MUTEX_NUSERS_AFTER_KIND  (__WORDSIZE != 64)
 #define __PTHREAD_MUTEX_USE_UNION          (__WORDSIZE != 64)
 
diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
index f631f0a..06361e6 100644
--- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
@@ -22,6 +22,11 @@
 #include <unistd.h>
 #include <dl-procinfo.h>
 
+#if HAVE_TUNABLES
+# define TUNABLE_NAMESPACE elision
+#endif
+#include <elf/dl-tunables.h>
+
 /* Reasonable initial tuning values, may be revised in the future.
    This is a conservative initial value.  */
 
@@ -50,7 +55,52 @@ struct elision_config __elision_aconf =
    DEFAULT locks should be automatically use elision in pthread_mutex_lock().
    Disabled for suid programs.  Only used when elision is available.  */
 
-int __pthread_force_elision attribute_hidden;
+int __pthread_force_elision attribute_hidden = 0;
+
+#if HAVE_TUNABLES
+static inline void
+__always_inline
+do_set_elision_enable (int32_t elision_enable)
+{
+  /* Enable elision if it's avaliable in hardware. It's not necessary to check
+     if __libc_enable_secure isn't enabled since elision_enable will be set
+     according to the default, which is disabled.  */
+  if (elision_enable == 1)
+    __pthread_force_elision = (GLRO (dl_hwcap2)
+			       & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
+}
+
+/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
+   should be disabled or enabled respectively.  The feature will only be used
+   if it's supported by the hardware.  */
+
+void
+TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
+{
+  int32_t elision_enable = (int32_t) valp->numval;
+  do_set_elision_enable (elision_enable);
+}
+
+#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
+static inline void						\
+__always_inline							\
+do_set_elision_ ## __name (__type value)			\
+{								\
+  __elision_aconf.__name = value;				\
+}								\
+void								\
+TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
+{								\
+  __type value = (__type) (valp)->numval;			\
+  do_set_elision_ ## __name (value);				\
+}
+
+TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
+TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
+#endif
 
 /* Initialize elision.  */
 
@@ -59,13 +109,26 @@ elision_init (int argc __attribute__ ((unused)),
 	      char **argv  __attribute__ ((unused)),
 	      char **environ)
 {
-#ifdef ENABLE_LOCK_ELISION
-  int elision_available = (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
-  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
+#if HAVE_TUNABLES
+  /* Elision depends on tunables and must be explicitly turned on by setting
+     the appropriate tunable on a supported platform.  */
+
+  TUNABLE_GET (enable, int32_t,
+	       TUNABLE_CALLBACK (set_elision_enable));
+  TUNABLE_GET (skip_lock_busy, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_busy));
+  TUNABLE_GET (skip_lock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
+  TUNABLE_GET (skip_lock_after_retries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
+  TUNABLE_GET (tries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_try_tbegin));
+  TUNABLE_GET (skip_trylock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
 #endif
+
   if (!__pthread_force_elision)
-    /* Disable elision on rwlocks.  */
-    __elision_aconf.try_tbegin = 0;
+    __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks.  */
 }
 
 #ifdef SHARED
diff --git a/sysdeps/unix/sysv/linux/powerpc/force-elision.h b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
index 318f791..d1feeeb 100644
--- a/sysdeps/unix/sysv/linux/powerpc/force-elision.h
+++ b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
@@ -16,7 +16,6 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#ifdef ENABLE_LOCK_ELISION
 /* Automatically enable elision for existing user lock kinds.  */
 #define FORCE_ELISION(m, s)						\
   if (__pthread_force_elision						\
@@ -25,4 +24,3 @@
       mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;			\
       s;								\
     }
-#endif
diff --git a/sysdeps/unix/sysv/linux/s390/Makefile b/sysdeps/unix/sysv/linux/s390/Makefile
index c5f544d..77f3852 100644
--- a/sysdeps/unix/sysv/linux/s390/Makefile
+++ b/sysdeps/unix/sysv/linux/s390/Makefile
@@ -16,7 +16,6 @@ sysdep_routines += dl-vdso
 endif
 
 ifeq ($(subdir),nptl)
-ifeq ($(enable-lock-elision),yes)
 libpthread-sysdep_routines += elision-lock elision-unlock elision-timed \
 			      elision-trylock
 
@@ -26,7 +25,6 @@ CFLAGS-elision-timed.c = $(elision-CFLAGS)
 CFLAGS-elision-trylock.c = $(elision-CFLAGS)
 CFLAGS-elision-unlock.c = $(elision-CFLAGS)
 endif
-endif
 
 ifeq ($(subdir),misc)
 tests += tst-ptrace-singleblock
diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.c b/sysdeps/unix/sysv/linux/s390/elision-conf.c
index cc0fdef..ab334cb 100644
--- a/sysdeps/unix/sysv/linux/s390/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/s390/elision-conf.c
@@ -22,6 +22,11 @@
 #include <unistd.h>
 #include <dl-procinfo.h>
 
+#if HAVE_TUNABLES
+# define TUNABLE_NAMESPACE elision
+#endif
+#include <elf/dl-tunables.h>
+
 /* Reasonable initial tuning values, may be revised in the future.
    This is a conservative initial value.  */
 
@@ -53,6 +58,50 @@ struct elision_config __elision_aconf =
 
 int __pthread_force_elision attribute_hidden = 0;
 
+#if HAVE_TUNABLES
+static inline void
+__always_inline
+do_set_elision_enable (int32_t elision_enable)
+{
+  /* Enable elision if it's avaliable in hardware. It's not necessary to check
+     if __libc_enable_secure isn't enabled since elision_enable will be set
+     according to the default, which is disabled.  */
+  if (elision_enable == 1)
+    __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
+}
+
+/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
+   should be disabled or enabled respectively.  The feature will only be used
+   if it's supported by the hardware.  */
+
+void
+TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
+{
+  int32_t elision_enable = (int32_t) valp->numval;
+  do_set_elision_enable (elision_enable);
+}
+
+#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
+static inline void						\
+__always_inline							\
+do_set_elision_ ## __name (__type value)			\
+{								\
+  __elision_aconf.__name = value;				\
+}								\
+void								\
+TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
+{								\
+  __type value = (__type) (valp)->numval;			\
+  do_set_elision_ ## __name (value);				\
+}
+
+TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
+TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
+#endif
+
 /* Initialize elison.  */
 
 static void
@@ -60,11 +109,26 @@ elision_init (int argc __attribute__ ((unused)),
 	      char **argv  __attribute__ ((unused)),
 	      char **environ)
 {
-  /* Set when the CPU and the kernel supports transactional execution.
-     When false elision is never attempted.  */
-  int elision_available = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
+#if HAVE_TUNABLES
+  /* Elision depends on tunables and must be explicitly turned on by setting
+     the appropriate tunable on a supported platform.  */
+
+  TUNABLE_GET (enable, int32_t,
+	       TUNABLE_CALLBACK (set_elision_enable));
+  TUNABLE_GET (skip_lock_busy, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_busy));
+  TUNABLE_GET (skip_lock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
+  TUNABLE_GET (skip_lock_after_retries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
+  TUNABLE_GET (tries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_try_tbegin));
+  TUNABLE_GET (skip_trylock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
+#endif
 
-  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
+  if (!__pthread_force_elision)
+    __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks.  */
 }
 
 #ifdef SHARED
diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.h b/sysdeps/unix/sysv/linux/s390/elision-conf.h
index 3143f3b..32f0ed3 100644
--- a/sysdeps/unix/sysv/linux/s390/elision-conf.h
+++ b/sysdeps/unix/sysv/linux/s390/elision-conf.h
@@ -15,7 +15,6 @@
    You should have received a copy of the GNU Lesser General Public
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
-#ifdef ENABLE_LOCK_ELISION
 #ifndef _ELISION_CONF_H
 #define _ELISION_CONF_H 1
 
@@ -41,4 +40,3 @@ extern int __pthread_force_elision attribute_hidden;
 #define HAVE_ELISION 1
 
 #endif
-#endif
diff --git a/sysdeps/unix/sysv/linux/s390/force-elision.h b/sysdeps/unix/sysv/linux/s390/force-elision.h
index 3ae3bcd..8e1e33e 100644
--- a/sysdeps/unix/sysv/linux/s390/force-elision.h
+++ b/sysdeps/unix/sysv/linux/s390/force-elision.h
@@ -16,7 +16,6 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#ifdef ENABLE_LOCK_ELISION
 /* Automatically enable elision for existing user lock kinds.  */
 #define FORCE_ELISION(m, s)						\
   if (__pthread_force_elision						\
@@ -25,4 +24,3 @@
       mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;			\
       s;								\
     }
-#endif
diff --git a/sysdeps/unix/sysv/linux/s390/lowlevellock.h b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
index 604137f..48f87a8 100644
--- a/sysdeps/unix/sysv/linux/s390/lowlevellock.h
+++ b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
@@ -22,7 +22,6 @@
 #include <sysdeps/nptl/lowlevellock.h>
 
 /* Transactional lock elision definitions.  */
-# ifdef ENABLE_LOCK_ELISION
 extern int __lll_timedlock_elision
   (int *futex, short *adapt_count, const struct timespec *timeout, int private)
   attribute_hidden;
@@ -45,6 +44,5 @@ extern int __lll_trylock_elision(int *futex, short *adapt_count)
   __lll_unlock_elision (&(futex), &(adapt_count), private)
 #  define lll_trylock_elision(futex, adapt_count) \
   __lll_trylock_elision(&(futex), &(adapt_count))
-# endif  /* ENABLE_LOCK_ELISION */
 
 #endif	/* lowlevellock.h */
diff --git a/sysdeps/unix/sysv/linux/x86/elision-conf.c b/sysdeps/unix/sysv/linux/x86/elision-conf.c
index 673b000..7e9fbf9 100644
--- a/sysdeps/unix/sysv/linux/x86/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/x86/elision-conf.c
@@ -22,6 +22,11 @@
 #include <elision-conf.h>
 #include <unistd.h>
 
+#if HAVE_TUNABLES
+# define TUNABLE_NAMESPACE elision
+#endif
+#include <elf/dl-tunables.h>
+
 /* Reasonable initial tuning values, may be revised in the future.
    This is a conservative initial value.  */
 
@@ -48,21 +53,76 @@ struct elision_config __elision_aconf =
    pthread_mutex_lock().  Disabled for suid programs.  Only used when elision
    is available.  */
 
-int __pthread_force_elision attribute_hidden;
+int __pthread_force_elision attribute_hidden = 0;
+
+#if HAVE_TUNABLES
+static inline void
+__always_inline
+do_set_elision_enable (int32_t elision_enable)
+{
+  /* Enable elision if it's avaliable in hardware. It's not necessary to check
+     if __libc_enable_secure isn't enabled since elision_enable will be set
+     according to the default, which is disabled.  */
+  if (elision_enable == 1)
+    __pthread_force_elision = HAS_CPU_FEATURE (RTM) ? 1 : 0;
+}
+
+/* The pthread->elision_enable tunable is 0 or 1 indicating that elision
+   should be disabled or enabled respectively.  The feature will only be used
+   if it's supported by the hardware.  */
 
-/* Initialize elison.  */
+void
+TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
+{
+  int32_t elision_enable = (int32_t) valp->numval;
+  do_set_elision_enable (elision_enable);
+}
+
+#define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
+static inline void						\
+__always_inline							\
+do_set_elision_ ## __name (__type value)			\
+{								\
+  __elision_aconf.__name = value;				\
+}								\
+void								\
+TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
+{								\
+  __type value = (__type) (valp)->numval;			\
+  do_set_elision_ ## __name (value);				\
+}
+
+TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
+TUNABLE_CALLBACK_FNDECL (retry_try_xbegin, int32_t);
+TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
+#endif
+
+/* Initialize elision.  */
 
 static void
 elision_init (int argc __attribute__ ((unused)),
 	      char **argv  __attribute__ ((unused)),
 	      char **environ)
 {
-  int elision_available = HAS_CPU_FEATURE (RTM);
-#ifdef ENABLE_LOCK_ELISION
-  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
+#if HAVE_TUNABLES
+  /* Elision depends on tunables and must be explicitly turned on by setting
+     the appropriate tunable on a supported platform.  */
+
+  TUNABLE_GET (enable, int32_t,
+	       TUNABLE_CALLBACK (set_elision_enable));
+  TUNABLE_GET (skip_lock_busy, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_busy));
+  TUNABLE_GET (skip_lock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
+  TUNABLE_GET (tries, int32_t,
+	       TUNABLE_CALLBACK (set_elision_retry_try_xbegin));
+  TUNABLE_GET (skip_trylock_internal_abort, int32_t,
+	       TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
 #endif
-  if (!elision_available)
-    __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */
+
+  if (!__pthread_force_elision)
+    __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks.  */
 }
 
 #ifdef SHARED