powerpc: Add the lock elision using HTM

This patch adds support for lock elision using ISA 2.07 hardware
transactional memory instructions for pthread_mutex primitives.
Similar to s390 version, the for elision logic defined in
'force-elision.h' is only enabled if ENABLE_LOCK_ELISION is defined.

Also, the lock elision code should be able to be built even with
a compiler that does not provide HTM support with builtins.
However I have noted the performance is sub-optimal due scheduling
pressures.

1 files changed, 80 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
new file mode 100644
index 0000000000..1d962e1d20
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
@@ -0,0 +1,80 @@
+/* elision-conf.c: Lock elision tunable parameters.
+   Copyright (C) 2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   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/>.  */
+
+#include "config.h"
+#include <pthreadP.h>
+#include <elision-conf.h>
+#include <unistd.h>
+#include <dl-procinfo.h>
+
+/* Reasonable initial tuning values, may be revised in the future.
+   This is a conservative initial value.  */
+
+struct elision_config __elision_aconf =
+  {
+    /* How many times to use a non-transactional lock after a transactional
+       failure has occurred because the lock is already acquired.  Expressed
+       in number of lock acquisition attempts.  */
+    .skip_lock_busy = 3,
+    /* How often to not attempt to use elision if a transaction aborted due
+       to reasons other than other threads' memory accesses.  Expressed in
+       number of lock acquisition attempts.  */
+    .skip_lock_internal_abort = 3,
+    /* How often to not attempt to use elision if a lock used up all retries
+       without success.  Expressed in number of lock acquisition attempts.  */
+    .skip_lock_out_of_tbegin_retries = 3,
+    /* How often we retry using elision if there is chance for the transaction
+       to finish execution (e.g., it wasn't aborted due to the lock being
+       already acquired.  */
+    .try_tbegin = 3,
+    /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock.  */
+    .skip_trylock_internal_abort = 3,
+  };
+
+/* Force elision for all new locks.  This is used to decide whether existing
+   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;
+
+/* Initialize elision.  */
+
+static void
+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;
+#endif
+}
+
+#ifdef SHARED
+# define INIT_SECTION ".init_array"
+# define MAYBE_CONST
+#else
+# define INIT_SECTION ".preinit_array"
+# define MAYBE_CONST const
+#endif
+
+void (*MAYBE_CONST __pthread_init_array []) (int, char **, char **)
+  __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
+{
+  &elision_init
+};