[PATCH v2 2/3] PowerPC: Add adaptive elision to rwlocks

[Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>]

This patch adds support for lock elision using ISA 2.07 hardware
transactional memory for rwlocks.  The logic is similar to the
one presented in pthread_mutex lock elision.

Tested on powerpc64 and powerpc32.

Changed from previous version:
- Cosmetics fixes from Will Schmidt

--

	* sysdeps/powerpc/nptl/elide.h: New file: generic lock elision support
	for powerpc.
	* sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
	[pthread_rwlock_t] (__pad1): Change size to 7 bytes in 64 bits case
	and remove it for 32 bits case.
	[pthread_rwlock_t] (__rwelision): New field for lock elision.
	(__PTHREAD_RWLOCK_ELISION_EXTRA): Adjust for new lock elision field
	initialization.
	* sysdeps/unix/sysv/linux/powerpc/elision-conf.c (elision_init):
	Disable lock elision with rdlocks if elision is not available.

--

diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
new file mode 100644
index 0000000..01572d9
--- /dev/null
+++ b/sysdeps/powerpc/nptl/elide.h
@@ -0,0 +1,111 @@
+/* elide.h: Generic lock elision support for powerpc.
+   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/>.  */
+
+#ifndef ELIDE_PPC_H
+# define ELIDE_PPC_H
+
+#ifdef ENABLE_LOCK_ELISION
+# include <htm.h>
+# include <elision-conf.h>
+
+/* Returns true if the lock defined by is_lock_free as elided.
+   ADAPT_COUNT is a pointer to per-lock state variable. */
+
+static inline bool
+__elide_lock (uint8_t *adapt_count, int is_lock_free)
+{
+  if (*adapt_count > 0)
+    {
+      (*adapt_count)--;
+      return false;
+    }
+
+  for (int i = __elision_aconf.try_tbegin; i > 0; i--)
+    {
+      if (__builtin_tbegin (0))
+	{
+	  if (is_lock_free)
+	    return true;
+	  /* Lock was busy.  */
+	  __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 (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
+	    {
+	      if (__elision_aconf.skip_lock_internal_abort > 0)
+		*adapt_count = __elision_aconf.skip_lock_internal_abort;
+	      break;
+	    }
+	  /* Same logic as above, but for a number of temporary failures in a
+	     a row.  */
+	  else if (__elision_aconf.skip_lock_out_of_tbegin_retries > 0
+		   && __elision_aconf.try_tbegin > 0)
+	    *adapt_count = __elision_aconf.skip_lock_out_of_tbegin_retries;
+	}
+     }
+
+  return false;
+}
+
+# define ELIDE_LOCK(adapt_count, is_lock_free) \
+  __elide_lock (&(adapt_count), is_lock_free)
+
+
+static inline bool
+__elide_trylock (uint8_t *adapt_count, int is_lock_free, int write)
+{
+  if (__elision_aconf.try_tbegin > 0)
+    {
+      if (write)
+	__builtin_tabort (_ABORT_NESTED_TRYLOCK);
+      return __elide_lock (adapt_count, is_lock_free);
+    }
+  return false;
+}
+
+# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write)	\
+  __elide_trylock (&(adapt_count), is_lock_free, write)
+
+
+static inline bool
+__elide_unlock (int is_lock_free)
+{
+  if (is_lock_free)
+    {
+      __builtin_tend (0);
+      return true;
+    }
+  return false;
+}
+
+# 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/unix/sysv/linux/powerpc/bits/pthreadtypes.h b/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
index 396a3d9..998f6d4 100644
--- a/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
+++ b/sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
@@ -172,11 +172,13 @@ typedef union
     unsigned int __nr_writers_queued;
     int __writer;
     int __shared;
-    unsigned long int __pad1;
+    unsigned char __rwelision;
+    unsigned char __pad1[7];
     unsigned long int __pad2;
     /* FLAGS must stay at this position in the structure to maintain
        binary compatibility.  */
     unsigned int __flags;
+# define __PTHREAD_RWLOCK_ELISION_EXTRA 0, {0, 0, 0, 0, 0, 0, 0 }
   } __data;
 # else
   struct
@@ -187,20 +189,20 @@ typedef union
     unsigned int __writer_wakeup;
     unsigned int __nr_readers_queued;
     unsigned int __nr_writers_queued;
-    unsigned char __pad1;
+    unsigned char __rwelision;
     unsigned char __pad2;
     unsigned char __shared;
     /* FLAGS must stay at this position in the structure to maintain
        binary compatibility.  */
     unsigned char __flags;
     int __writer;
+#define __PTHREAD_RWLOCK_ELISION_EXTRA 0
   } __data;
 # endif
   char __size[__SIZEOF_PTHREAD_RWLOCK_T];
   long int __align;
 } pthread_rwlock_t;
 
-#define __PTHREAD_RWLOCK_ELISION_EXTRA 0
 
 typedef union
 {
diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
index 1d962e1..70fbbb2 100644
--- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
@@ -63,6 +63,9 @@ elision_init (int argc __attribute__ ((unused)),
   int elision_available = (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
   __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
 #endif
+  if (!__pthread_force_elision)
+    /* Disable elision on rwlocks.  */
+    __elision_aconf.try_tbegin = 0;
 }
 
 #ifdef SHARED