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, 68 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-trylock.c b/sysdeps/unix/sysv/linux/powerpc/elision-trylock.c
new file mode 100644
index 0000000000..4a310d5945
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-trylock.c
@@ -0,0 +1,68 @@
+/* elision-trylock.c: Lock eliding trylock for pthreads.
+   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 <pthread.h>
+#include <pthreadP.h>
+#include <lowlevellock.h>
+#include <elision-conf.h>
+#include "htm.h"
+
+#define aconf __elision_aconf
+
+/* Try to elide a futex trylock.  FUTEX is the futex variable.  ADAPT_COUNT is
+   the adaptation counter in the mutex.  */
+
+int
+__lll_trylock_elision (int *futex, short *adapt_count)
+{
+  /* Implement POSIX semantics by forbiding nesting elided trylocks.  */
+  __builtin_tabort (_ABORT_NESTED_TRYLOCK);
+
+  /* Only try a transaction if it's worth it.  */
+  if (*adapt_count > 0)
+    {
+      (*adapt_count)--;
+      goto use_lock;
+    }
+
+  if (__builtin_tbegin (0))
+    {
+      if (*futex == 0)
+	return 0;
+
+      /* Lock was busy.  Fall back to normal locking.  */
+      __builtin_tabort (_ABORT_LOCK_BUSY);
+    }
+  else
+    {
+      if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
+	{
+	  /* A persistent failure indicates that a retry will probably
+	     result in another failure.  Use normal locking now and
+	     for the next couple of calls.  */
+	  if (aconf.skip_trylock_internal_abort > 0)
+	    *adapt_count = aconf.skip_trylock_internal_abort;
+	}
+
+	if (aconf.skip_lock_busy > 0)
+	  *adapt_count = aconf.skip_lock_busy;
+    }
+
+use_lock:
+  return lll_trylock (*futex);
+}