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>

1 files changed, 67 insertions, 7 deletions

diff --git a/sysdeps/unix/sysv/linux/x86/elision-conf.c b/sysdeps/unix/sysv/linux/x86/elision-conf.c
index 673b0005a7..7e9fbf9382 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