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, 107 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-lock.c b/sysdeps/unix/sysv/linux/powerpc/elision-lock.c
new file mode 100644
index 0000000..2ce75b2
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-lock.c
@@ -0,0 +1,107 @@
+/* elision-lock.c: Elided pthread mutex lock.
+   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 <stdio.h>
+#include <pthread.h>
+#include <pthreadP.h>
+#include <lowlevellock.h>
+#include <elision-conf.h>
+#include "htm.h"
+
+/* PowerISA 2.0.7 Section B.5.5 defines isync to be insufficient as a
+   barrier in acquire mechanism for HTM operations, a strong 'sync' is
+   required.  */
+#undef __arch_compare_and_exchange_val_32_acq
+#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval)           \
+  ({                                                                          \
+      __typeof (*(mem)) __tmp;                                                \
+      __typeof (mem)  __memp = (mem);                                         \
+      __asm __volatile (                                                      \
+                        "1:     lwarx   %0,0,%1" MUTEX_HINT_ACQ "\n"          \
+                        "       cmpw    %0,%2\n"                              \
+                        "       bne     2f\n"                                 \
+                        "       stwcx.  %3,0,%1\n"                            \
+                        "       bne-    1b\n"                                 \
+                        "2:     sync"                                         \
+                        : "=&r" (__tmp)                                       \
+                        : "b" (__memp), "r" (oldval), "r" (newval)            \
+                        : "cr0", "memory");                                   \
+      __tmp;                                                                  \
+  })
+
+#if !defined(LLL_LOCK) && !defined(EXTRAARG)
+/* Make sure the configuration code is always linked in for static
+   libraries.  */
+#include "elision-conf.c"
+#endif
+
+#ifndef EXTRAARG
+# define EXTRAARG
+#endif
+#ifndef LLL_LOCK
+# define LLL_LOCK(a,b) lll_lock(a,b), 0
+#endif
+
+#define aconf __elision_aconf
+
+/* Adaptive lock using transactions.
+   By default the lock region is run as a transaction, and when it
+   aborts or the lock is busy the lock adapts itself.  */
+
+int
+__lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
+{
+  if (*adapt_count > 0)
+    {
+      (*adapt_count)--;
+      goto use_lock;
+    }
+
+  int try_begin = aconf.try_tbegin;
+  while (1)
+    {
+      if (__builtin_tbegin (0))
+	{
+	  if (*lock == 0)
+	    return 0;
+	  /* Lock was busy.  Fall back to normal locking.  */
+	  __builtin_tabort (_ABORT_LOCK_BUSY);
+	}
+      else
+	{
+	  /* 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 (try_begin-- <= 0
+	      || _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
+	    {
+	      if (aconf.skip_lock_internal_abort > 0)
+		*adapt_count = aconf.skip_lock_internal_abort;
+	      goto use_lock;
+	    }
+	  /* Same logic as above, but for for a number of temporary failures
+	     in a row.  */
+	  else if (aconf.skip_lock_out_of_tbegin_retries > 0
+                   && aconf.try_tbegin > 0)
+	    *adapt_count = aconf.skip_lock_out_of_tbegin_retries;
+	}
+     }
+
+use_lock:
+  return LLL_LOCK ((*lock), pshared);
+}