S/390: Port of lock elision to System/z

Added support for TX lock elision of pthread mutexes on s390 and
s390x.  This may improve lock scaling of existing programs on TX
capable systems.  The lock elision code is only built with
--enable-lock-elision=yes and then requires a GCC version supporting
the TX builtins.  With lock elision default mutexes are elided via
__builtin_tbegin, if the cpu supports transactions. By default lock
elision is not enabled and the elision code is not built.

21 files changed, 693 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index cd9dec29c9..a64ca9f269 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,38 @@
+2014-05-09  Dominik Vogt  <vogt@linux.vnet.ibm.com>
+	    Stefan Liebler  <stli@linux.vnet.ibm.com>
+
+	* config.make.in (enable-lock-elision): New Makefile variable.
+	* configure.ac: Likewise.
+	* configure: Regenerate.
+	* sysdeps/s390/configure.ac:
+	Add check for gcc transactions support.
+	* sysdeps/s390/configure: Regenerate.
+	* nptl/sysdeps/unix/sysv/linux/s390/Makefile: New file.
+	Build elision files if enabled.
+	* nptl/sysdeps/unix/sysv/linux/s390/elision-conf.c: New file.
+	Add lock elision support for s390.
+	* nptl/sysdeps/unix/sysv/linux/s390/elision-conf.h: Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c: Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/elision-timed.c: Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/elision-trylock.c: Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/elision-unlock.c: Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/force-elision.h: Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_cond_lock.c:
+	Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_lock.c:
+	Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_timedlock.c:
+	Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_trylock.c:
+	Likewise.
+	* nptl/sysdeps/unix/sysv/linux/s390/lowlevellock.h:
+	(__lll_timedlock_elision, __lll_lock_elision)
+	(__lll_unlock_elision, __lll_trylock_elision)
+	(lll_timedlock_elision, lll_lock_elision)
+	(lll_unlock_elision, lll_trylock_elision): Add.
+	* nptl/sysdeps/unix/sysv/linux/s390/bits/pthreadtypes.h
+	(pthread_mutex_t): Add lock elision support for s390.
+
 2014-05-09  Will Newton  <will.newton@linaro.org>
 
 	* sysdeps/arm/armv7/strcmp.S: New file.
diff --git a/NEWS b/NEWS
index 40068712dc..fae2b82607 100644
--- a/NEWS
+++ b/NEWS
@@ -40,6 +40,14 @@ Version 2.20
   test macros defined.
 
 * Optimized strcmp implementation for ARMv7.  Contributed by ARM Ltd.
+
+* Added support for TX lock elision of pthread mutexes on s390 and s390x.
+  This may improve lock scaling of existing programs on TX capable systems.
+  The lock elision code is only built with --enable-lock-elision=yes and
+  then requires a GCC version supporting the TX builtins.  With lock elision
+  default mutexes are elided via __builtin_tbegin, if the cpu supports
+  transactions. By default lock elision is not enabled and the elision code
+  is not built.
 
 Version 2.19
 
diff --git a/config.make.in b/config.make.in
index 132d17920c..6bcab8adb1 100644
--- a/config.make.in
+++ b/config.make.in
@@ -93,6 +93,7 @@ build-nscd = @build_nscd@
 use-nscd = @use_nscd@
 build-hardcoded-path-in-tests= @hardcoded_path_in_tests@
 build-pt-chown = @build_pt_chown@
+enable-lock-elision = @enable_lock_elision@
 
 # Build tools.
 CC = @CC@
diff --git a/configure b/configure
index 8b0b22241d..ecc282bd2e 100755
--- a/configure
+++ b/configure
@@ -651,6 +651,7 @@ libc_cv_nss_crypt
 all_warnings
 force_install
 bindnow
+enable_lock_elision
 hardcoded_path_in_tests
 oldest_abi
 use_default_link
@@ -3476,6 +3477,7 @@ else
   enable_lock_elision=no
 fi
 
+
 if test "$enable_lock_elision" = yes ; then
   $as_echo "#define ENABLE_LOCK_ELISION 1" >>confdefs.h
 
diff --git a/configure.ac b/configure.ac
index 97a959114d..babfe5713c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -184,6 +184,7 @@ AC_ARG_ENABLE([lock-elision],
 			     [Enable lock elision for pthread mutexes by default]),
 	      [enable_lock_elision=$enableval],
 	      [enable_lock_elision=no])
+AC_SUBST(enable_lock_elision)
 if test "$enable_lock_elision" = yes ; then
   AC_DEFINE(ENABLE_LOCK_ELISION)
 fi
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/Makefile b/nptl/sysdeps/unix/sysv/linux/s390/Makefile
new file mode 100644
index 0000000000..269832f999
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/Makefile
@@ -0,0 +1,10 @@
+ifeq ($(enable-lock-elision),yes)
+libpthread-sysdep_routines += elision-lock elision-unlock elision-timed \
+			      elision-trylock
+
+elision-CFLAGS = -mhtm
+CFLAGS-elision-lock.c = $(elision-CFLAGS)
+CFLAGS-elision-timed.c = $(elision-CFLAGS)
+CFLAGS-elision-trylock.c = $(elision-CFLAGS)
+CFLAGS-elision-unlock.c = $(elision-CFLAGS)
+endif
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/bits/pthreadtypes.h b/nptl/sysdeps/unix/sysv/linux/s390/bits/pthreadtypes.h
index 8264de0591..d70f8b35b1 100644
--- a/nptl/sysdeps/unix/sysv/linux/s390/bits/pthreadtypes.h
+++ b/nptl/sysdeps/unix/sysv/linux/s390/bits/pthreadtypes.h
@@ -89,14 +89,37 @@ typedef union
        binary compatibility.  */
     int __kind;
 #if __WORDSIZE == 64
+# ifdef ENABLE_LOCK_ELISION
+    short __spins;
+    short __elision;
+    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
+#  define __PTHREAD_SPINS               0, 0
+# else
     int __spins;
+    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
+#  define __PTHREAD_SPINS               0
+# endif
     __pthread_list_t __list;
 # define __PTHREAD_MUTEX_HAVE_PREV	1
 #else
     unsigned int __nusers;
     __extension__ union
     {
+# ifdef ENABLE_LOCK_ELISION
+      struct
+      {
+	short __espins;
+	short __elision;
+      } _d;
+#  define __spins _d.__espins
+#  define __elision _d.__elision
+    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
+#  define __PTHREAD_SPINS               { 0, 0 }
+# else
       int __spins;
+    /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
+#  define __PTHREAD_SPINS               0
+# endif
       __pthread_slist_t __list;
     };
 #endif
@@ -105,8 +128,6 @@ typedef union
   long int __align;
 } pthread_mutex_t;
 
-/* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER.  */
-#define __PTHREAD_SPINS 0
 
 typedef union
 {
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-conf.c b/nptl/sysdeps/unix/sysv/linux/s390/elision-conf.c
new file mode 100644
index 0000000000..69c04836ed
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-conf.c
@@ -0,0 +1,82 @@
+/* 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 often to not attempt to use elision if a transaction aborted
+       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 try 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 upgraded to elision in
+   pthread_mutex_lock().  Disabled for suid programs.  Only used when elision
+   is available.  */
+
+int __pthread_force_elision attribute_hidden = 0;
+
+/* Initialize elison.  */
+
+static void
+elision_init (int argc __attribute__ ((unused)),
+	      char **argv  __attribute__ ((unused)),
+	      char **environ)
+{
+  /* Set when the CPU and the kernel supports transactional execution.
+     When false elision is never attempted.  */
+  int elision_available = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
+
+  __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
+}
+
+#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
+};
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-conf.h b/nptl/sysdeps/unix/sysv/linux/s390/elision-conf.h
new file mode 100644
index 0000000000..d9e97947a0
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-conf.h
@@ -0,0 +1,44 @@
+/* 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/>.  */
+#ifdef ENABLE_LOCK_ELISION
+#ifndef _ELISION_CONF_H
+#define _ELISION_CONF_H 1
+
+#include <pthread.h>
+#include <time.h>
+
+/* Should make sure there is no false sharing on this.  */
+
+struct elision_config
+{
+  int skip_lock_busy;
+  int skip_lock_internal_abort;
+  int skip_lock_out_of_tbegin_retries;
+  int try_tbegin;
+  int skip_trylock_internal_abort;
+};
+
+extern struct elision_config __elision_aconf attribute_hidden;
+
+extern int __pthread_force_elision attribute_hidden;
+
+/* Tell the test suite to test elision for this architecture.  */
+#define HAVE_ELISION 1
+
+#endif
+#endif
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c b/nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c
new file mode 100644
index 0000000000..ba5338fbb9
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c
@@ -0,0 +1,119 @@
+/* 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 <pthread.h>
+#include <pthreadP.h>
+#include <lowlevellock.h>
+#include <htmintrin.h>
+#include <elision-conf.h>
+#include <stdint.h>
+
+#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 *futex, short *adapt_count, EXTRAARG int private)
+{
+  if (*adapt_count > 0)
+    {
+      /* Lost updates are possible, but harmless.  Due to races this might lead
+	 to *adapt_count becoming less than zero.  */
+      (*adapt_count)--;
+      goto use_lock;
+    }
+
+  __asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t"
+		    ".machine \"all\""
+		    : : : "memory");
+
+  int try_tbegin;
+  for (try_tbegin = aconf.try_tbegin;
+       try_tbegin > 0;
+       try_tbegin--)
+    {
+      unsigned status;
+      if (__builtin_expect
+	  ((status = __builtin_tbegin((void *)0)) == _HTM_TBEGIN_STARTED, 1))
+	{
+	  if (*futex == 0)
+	    return 0;
+	  /* Lock was busy.  Fall back to normal locking.  */
+	  if (__builtin_expect (__builtin_tx_nesting_depth (), 1))
+	    {
+	      /* In a non-nested transaction there is no need to abort,
+		 which is expensive.  */
+	      __builtin_tend ();
+	      if (aconf.skip_lock_busy > 0)
+		*adapt_count = aconf.skip_lock_busy;
+	      goto use_lock;
+	    }
+	  else /* nesting depth is > 1 */
+	    {
+	      /* A nested transaction will abort eventually because it
+		 cannot make any progress before *futex changes back to 0.
+		 So we may as well abort immediately.
+		 This persistently aborts the outer transaction to force
+		 the outer mutex use the default lock instead of retrying
+		 with transactions until the try_tbegin of the outer mutex
+		 is zero.
+		 The adapt_count of this inner mutex is not changed,
+		 because using the default lock with the inner mutex
+		 would abort the outer transaction.
+	      */
+	      __builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1);
+	    }
+	}
+      else
+	{
+	  if (status != _HTM_TBEGIN_TRANSIENT)
+	    {
+	      /* A persistent abort (cc 1 or 3) indicates that a retry is
+		 probably futile.  Use the normal locking now and for the
+		 next couple of calls.
+		 Be careful to avoid writing to the lock.  */
+	      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.  */
+  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 ((*futex), private);
+}
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-timed.c b/nptl/sysdeps/unix/sysv/linux/s390/elision-timed.c
new file mode 100644
index 0000000000..a8d8b2a348
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-timed.c
@@ -0,0 +1,26 @@
+/* Lock elision timed 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 <time.h>
+#include <elision-conf.h>
+#include <lowlevellock.h>
+#define __lll_lock_elision __lll_timedlock_elision
+#define EXTRAARG const struct timespec *t,
+#undef LLL_LOCK
+#define LLL_LOCK(a, b) lll_timedlock(a, t, b)
+#include "elision-lock.c"
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-trylock.c b/nptl/sysdeps/unix/sysv/linux/s390/elision-trylock.c
new file mode 100644
index 0000000000..61447d6bf4
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-trylock.c
@@ -0,0 +1,94 @@
+/* Elided pthread mutex trylock.
+   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 <htmintrin.h>
+#include <elision-conf.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)
+{
+  __asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t"
+		    ".machine \"all\""
+		    : : : "memory");
+
+  /* Implement POSIX semantics by forbiding nesting elided trylocks.
+     Sorry.  After the abort the code is re-executed
+     non transactional and if the lock was already locked
+     return an error.  */
+  if (__builtin_tx_nesting_depth () > 0)
+    {
+      /* Note that this abort may terminate an outermost transaction that
+	 was created outside glibc.
+	 This persistently aborts the current transactions to force
+	 them to use the default lock instead of retrying transactions
+	 until their try_tbegin is zero.
+      */
+      __builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1);
+    }
+
+  /* Only try a transaction if it's worth it.  */
+  if (*adapt_count <= 0)
+    {
+      unsigned status;
+
+      if (__builtin_expect
+	  ((status = __builtin_tbegin ((void *)0)) == _HTM_TBEGIN_STARTED, 1))
+	{
+	  if (*futex == 0)
+	    return 0;
+	  /* Lock was busy.  Fall back to normal locking.  */
+	  /* Since we are in a non-nested transaction there is no need to abort,
+	     which is expensive.  */
+	  __builtin_tend ();
+	  /* Note: Changing the adapt_count here might abort a transaction on a
+	     different cpu, but that could happen anyway when the futex is
+	     acquired, so there's no need to check the nesting depth here.  */
+	  if (aconf.skip_lock_busy > 0)
+	    *adapt_count = aconf.skip_lock_busy;
+	}
+      else
+	{
+	  if (status != _HTM_TBEGIN_TRANSIENT)
+	    {
+	      /* A persistent abort (cc 1 or 3) indicates that a retry is
+		 probably futile.  Use the normal locking now and for the
+		 next couple of calls.
+		 Be careful to avoid writing to the lock.  */
+	      if (aconf.skip_trylock_internal_abort > 0)
+		*adapt_count = aconf.skip_trylock_internal_abort;
+	    }
+	}
+      /* Could do some retries here.  */
+    }
+  else
+    {
+      /* Lost updates are possible, but harmless.  Due to races this might lead
+	 to *adapt_count becoming less than zero.  */
+      (*adapt_count)--;
+    }
+
+  return lll_trylock (*futex);
+}
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-unlock.c b/nptl/sysdeps/unix/sysv/linux/s390/elision-unlock.c
new file mode 100644
index 0000000000..9ceae3ee1e
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-unlock.c
@@ -0,0 +1,38 @@
+/* Commit an elided pthread 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 <pthreadP.h>
+#include <lowlevellock.h>
+
+int
+__lll_unlock_elision(int *futex, int private)
+{
+  /* If the lock is free, we elided the lock earlier.  This does not
+     necessarily mean that we are in a transaction, because the user code may
+     have closed the transaction, but that is impossible to detect reliably.  */
+  if (*futex == 0)
+    {
+      __asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t"
+			".machine \"all\""
+			: : : "memory");
+      __builtin_tend();
+    }
+  else
+    lll_unlock ((*futex), private);
+  return 0;
+}
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/force-elision.h b/nptl/sysdeps/unix/sysv/linux/s390/force-elision.h
new file mode 100644
index 0000000000..8fd7684d9a
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/force-elision.h
@@ -0,0 +1,33 @@
+/* Automatic enabling of elision for mutexes
+   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/>.  */
+
+#ifdef ENABLE_LOCK_ELISION
+/* Check for elision on this lock without upgrading.  */
+#define DO_ELISION(m)							\
+  (__pthread_force_elision						\
+   && (m->__data.__kind & PTHREAD_MUTEX_NO_ELISION_NP) == 0)		\
+
+/* Automatically enable elision for existing user lock kinds.  */
+#define FORCE_ELISION(m, s)						\
+  if (__pthread_force_elision						\
+      && (m->__data.__kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0)	\
+    {									\
+      mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;			\
+      s;								\
+    }
+#endif
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/lowlevellock.h b/nptl/sysdeps/unix/sysv/linux/s390/lowlevellock.h
index 864dcbccc0..cabff30be9 100644
--- a/nptl/sysdeps/unix/sysv/linux/s390/lowlevellock.h
+++ b/nptl/sysdeps/unix/sysv/linux/s390/lowlevellock.h
@@ -285,6 +285,15 @@ __lll_timedlock (int *futex, const struct timespec *abstime, int private)
 #define lll_timedlock(futex, abstime, private) \
   __lll_timedlock (&(futex), abstime, private)
 
+#ifdef ENABLE_LOCK_ELISION
+extern int __lll_timedlock_elision
+  (int *futex, short *adapt_count, const struct timespec *timeout, int private)
+  attribute_hidden;
+
+# define lll_timedlock_elision(futex, adapt_count, timeout, private)	\
+  __lll_timedlock_elision(&(futex), &(adapt_count), timeout, private)
+#endif
+
 static inline int
 __attribute__ ((always_inline))
 __lll_robust_timedlock (int *futex, const struct timespec *abstime,
@@ -360,4 +369,22 @@ extern int __lll_timedwait_tid (int *, const struct timespec *)
     __res;								      \
   })
 
+#ifdef ENABLE_LOCK_ELISION
+extern int __lll_lock_elision (int *futex, short *adapt_count, int private)
+  attribute_hidden;
+
+extern int __lll_unlock_elision(int *futex, int private)
+  attribute_hidden;
+
+extern int __lll_trylock_elision(int *futex, short *adapt_count)
+  attribute_hidden;
+
+# define lll_lock_elision(futex, adapt_count, private) \
+  __lll_lock_elision (&(futex), &(adapt_count), private)
+# define lll_unlock_elision(futex, private) \
+  __lll_unlock_elision (&(futex), private)
+# define lll_trylock_elision(futex, adapt_count) \
+  __lll_trylock_elision(&(futex), &(adapt_count))
+#endif
+
 #endif	/* lowlevellock.h */
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_cond_lock.c b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_cond_lock.c
new file mode 100644
index 0000000000..6fc0f969ef
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_cond_lock.c
@@ -0,0 +1,22 @@
+/* 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/>.  */
+
+/* The cond lock is not actually elided yet, but we still need to handle
+   already elided locks.  */
+#include <elision-conf.h>
+
+#include <nptl/sysdeps/unix/sysv/linux/pthread_mutex_cond_lock.c>
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_lock.c b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_lock.c
new file mode 100644
index 0000000000..6fd6a9866f
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_lock.c
@@ -0,0 +1,22 @@
+/* Elided version of 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 <elision-conf.h>
+#include <force-elision.h>
+
+#include <nptl/pthread_mutex_lock.c>
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_timedlock.c b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_timedlock.c
new file mode 100644
index 0000000000..d0e6537ecc
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_timedlock.c
@@ -0,0 +1,22 @@
+/* Elided version of pthread_mutex_timedlock.
+   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 <elision-conf.h>
+#include <force-elision.h>
+
+#include <nptl/pthread_mutex_timedlock.c>
diff --git a/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_trylock.c b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_trylock.c
new file mode 100644
index 0000000000..ea8a8fff93
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/pthread_mutex_trylock.c
@@ -0,0 +1,22 @@
+/* Elided version of pthread_mutex_trylock.
+   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 <elision-conf.h>
+#include <force-elision.h>
+
+#include <nptl/pthread_mutex_trylock.c>
diff --git a/sysdeps/s390/configure b/sysdeps/s390/configure
index c2d05f7b4a..6948cc2190 100644
--- a/sysdeps/s390/configure
+++ b/sysdeps/s390/configure
@@ -68,5 +68,41 @@ if test $ac_verc_fail = yes; then
 fi
 
 
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_tbegin" >&5
+$as_echo_n "checking for __builtin_tbegin... " >&6; }
+if ${libc_cv_gcc_builtin_tbegin+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.c <<\EOF
+#include <htmintrin.h>
+void testtransaction ()
+{
+  if (__builtin_tbegin (0) == _HTM_TBEGIN_STARTED)
+    {
+      __builtin_tend ();
+    }
+}
+EOF
+if { ac_try='${CC-cc} -mhtm -O2 -S conftest.c -o - | grep -w tbegin > /dev/null'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; } ;
+then
+  libc_cv_gcc_builtin_tbegin=yes
+else
+  libc_cv_gcc_builtin_tbegin=no
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_builtin_tbegin" >&5
+$as_echo "$libc_cv_gcc_builtin_tbegin" >&6; }
+
+if test "$enable_lock_elision" = yes && test "$libc_cv_gcc_builtin_tbegin" = no ; then
+   critic_missing="$critic_missing The used GCC has no support for __builtin_tbegin, which is needed for lock-elision on target S390."
+fi
+
 test -n "$critic_missing" && as_fn_error $? "
 *** $critic_missing" "$LINENO" 5
diff --git a/sysdeps/s390/configure.ac b/sysdeps/s390/configure.ac
index 59cfdd132a..493e9a469c 100644
--- a/sysdeps/s390/configure.ac
+++ b/sysdeps/s390/configure.ac
@@ -10,5 +10,31 @@ AC_CHECK_PROG_VER(AS, $AS, --version,
 		  [GNU assembler.* \([0-9]*\.[0-9.]*\)],
 		  [2.2[4-9]*|2.[3-9][0-9]*|[3-9].*|[1-9][0-9]*], critic_missing="$critic_missing The program AS is required in version >= 2.24 for target S390.")
 
+
+AC_CACHE_CHECK(for __builtin_tbegin, libc_cv_gcc_builtin_tbegin, [dnl
+cat > conftest.c <<\EOF
+#include <htmintrin.h>
+void testtransaction ()
+{
+  if (__builtin_tbegin (0) == _HTM_TBEGIN_STARTED)
+    {
+      __builtin_tend ();
+    }
+}
+EOF
+dnl
+dnl test, if the tbegin instruction is used by __builtin_tbegin
+if AC_TRY_COMMAND([${CC-cc} -mhtm -O2 -S conftest.c -o - | grep -w tbegin > /dev/null]) ;
+then
+  libc_cv_gcc_builtin_tbegin=yes
+else
+  libc_cv_gcc_builtin_tbegin=no
+fi
+rm -f conftest* ])
+
+if test "$enable_lock_elision" = yes && test "$libc_cv_gcc_builtin_tbegin" = no ; then
+   critic_missing="$critic_missing The used GCC has no support for __builtin_tbegin, which is needed for lock-elision on target S390."
+fi
+
 test -n "$critic_missing" && AC_MSG_ERROR([
 *** $critic_missing])