Add the low level infrastructure for pthreads lock elision with TSX

Lock elision using TSX is a technique to optimize lock scaling
It allows to run locks in parallel using hardware support for
a transactional execution mode in 4th generation Intel Core CPUs.
See http://www.intel.com/software/tsx for more Information.

This patch implements a simple adaptive lock elision algorithm based
on RTM. It enables elision for the pthread mutexes and rwlocks.
The algorithm keeps track whether a mutex successfully elides or not,
and stops eliding for some time when it is not.

When the CPU supports RTM the elision path is automatically tried,
otherwise any elision is disabled.

The adaptation algorithm and its tuning is currently preliminary.

The code adds some checks to the lock fast paths. Micro-benchmarks
show little to no difference without RTM.

This patch implements the low level "lll_" code for lock elision.
Followon patches hook this into the pthread implementation

Changes with the RTM mutexes:
-----------------------------
Lock elision in pthreads is generally compatible with existing programs.
There are some obscure exceptions, which are expected to be uncommon.
See the manual for more details.

- A broken program that unlocks a free lock will crash.
  There are ways around this with some tradeoffs (more code in hot paths)
  I'm still undecided on what approach to take here; have to wait for testing reports.
- pthread_mutex_destroy of a lock mutex will not return EBUSY but 0.
- There's also a similar situation with trylock outside the mutex,
  "knowing" that the mutex must be held due to some other condition.
  In this case an assert failure cannot be recovered. This situation is
  usually an existing bug in the program.
- Same applies to the rwlocks. Some of the return values changes
  (for example there is no EDEADLK for an elided lock, unless it aborts.
   However when elided it will also never deadlock of course)
- Timing changes, so broken programs that make assumptions about specific timing
  may expose already existing latent problems.  Note that these broken programs will
  break in other situations too (loaded system, new faster hardware, compiler
  optimizations etc.)
- Programs with non recursive mutexes that take them recursively in a thread and
  which would always deadlock without elision may not always see a deadlock.
  The deadlock will only happen on an early or delayed abort (which typically
  happens at some point)
  This only happens for mutexes not explicitely set to PTHREAD_MUTEX_NORMAL
  or PTHREAD_MUTEX_ADAPTIVE_NP.  PTHREAD_MUTEX_NORMAL mutexes do not elide.

The elision default can be set at configure time.

This patch implements the basic infrastructure for elision.

10 files changed, 480 insertions, 0 deletions

diff --git a/nptl/sysdeps/unix/sysv/linux/i386/lowlevellock.h b/nptl/sysdeps/unix/sysv/linux/i386/lowlevellock.h
index f665ac9e6b..cc3ec5ba26 100644
--- a/nptl/sysdeps/unix/sysv/linux/i386/lowlevellock.h
+++ b/nptl/sysdeps/unix/sysv/linux/i386/lowlevellock.h
@@ -430,6 +430,12 @@ LLL_STUB_UNWIND_INFO_END
 		       : "memory");					      \
      result; })
 
+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)
 
 #define lll_robust_timedlock(futex, timeout, id, private) \
   ({ int result, ignore1, ignore2, ignore3;				      \
@@ -583,6 +589,22 @@ extern int __lll_timedwait_tid (int *tid, const struct timespec *abstime)
       }									      \
     __result; })
 
+extern int __lll_lock_elision (int *futex, short *adapt_count, int private)
+  attribute_hidden;
+
+extern int __lll_unlock_elision(int *lock, int private)
+  attribute_hidden;
+
+extern int __lll_trylock_elision(int *lock, 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  /* !__ASSEMBLER__ */
 
 #endif	/* lowlevellock.h */
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/Makefile b/nptl/sysdeps/unix/sysv/linux/x86/Makefile
new file mode 100644
index 0000000000..61b7552bc9
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/Makefile
@@ -0,0 +1,3 @@
+libpthread-sysdep_routines += init-arch
+libpthread-sysdep_routines += elision-lock elision-unlock elision-timed \
+			      elision-trylock
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.c b/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.c
new file mode 100644
index 0000000000..6277e48d76
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.c
@@ -0,0 +1,87 @@
+/* elision-conf.c: Lock elision tunable parameters.
+   Copyright (C) 2013 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 <init-arch.h>
+#include <elision-conf.h>
+#include <unistd.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 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.  */
+    .retry_try_xbegin = 3,
+    /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock.  */
+    .skip_trylock_internal_abort = 3,
+  };
+
+/* Elided rwlock toggle, set when elision is available and is
+   enabled for rwlocks.  */
+
+int __rwlock_rtm_enabled attribute_hidden;
+
+/* Retries for elided rwlocks on read. Conservative initial value.  */
+
+int __rwlock_rtm_read_retries attribute_hidden = 3;
+
+/* Set when the CPU supports elision. When false elision is never attempted.  */
+
+int __elision_available attribute_hidden;
+
+/* 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;
+
+/* Initialize elison.  */
+
+static void
+elision_init (int argc __attribute__ ((unused)),
+	      char **argv  __attribute__ ((unused)),
+	      char **environ)
+{
+  __elision_available = HAS_RTM;
+  __pthread_force_elision = __libc_enable_secure ? 0 : __elision_available;
+  __rwlock_rtm_enabled = __libc_enable_secure ? 0 : __elision_available;
+}
+
+#ifdef SHARED
+# define INIT_SECTION ".init_array"
+#else
+# define INIT_SECTION ".preinit_array"
+#endif
+
+void (*const __pthread_init_array []) (int, char **, char **)
+  __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
+{
+  &elision_init
+};
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.h b/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.h
new file mode 100644
index 0000000000..55b81db930
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-conf.h
@@ -0,0 +1,44 @@
+/* elision-conf.h: Lock elision tunable parameters.
+   Copyright (C) 2013 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 _ELISION_CONF_H
+#define _ELISION_CONF_H 1
+
+#include <pthread.h>
+#include <cpuid.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 retry_try_xbegin;
+  int skip_trylock_internal_abort;
+};
+
+extern struct elision_config __elision_aconf attribute_hidden;
+
+extern int __rwlock_rtm_enabled attribute_hidden;
+extern int __elision_available attribute_hidden;
+extern int __pthread_force_elision attribute_hidden;
+
+/* Tell the test suite to test elision for this architecture.  */
+#define HAVE_ELISION 1
+
+#endif
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/elision-lock.c b/nptl/sysdeps/unix/sysv/linux/x86/elision-lock.c
new file mode 100644
index 0000000000..de16f1b02f
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-lock.c
@@ -0,0 +1,95 @@
+/* elision-lock.c: Elided pthread mutex lock.
+   Copyright (C) 2011-2013 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 "hle.h"
+#include <elision-conf.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)
+    {
+      unsigned status;
+      int try_xbegin;
+
+      for (try_xbegin = aconf.retry_try_xbegin;
+	   try_xbegin > 0;
+	   try_xbegin--)
+	{
+	  if ((status = _xbegin()) == _XBEGIN_STARTED)
+	    {
+	      if (*futex == 0)
+		return 0;
+
+	      /* Lock was busy. Fall back to normal locking.
+		 Could also _xend here but xabort with 0xff code
+		 is more visible in the profiler.  */
+	      _xabort (_ABORT_LOCK_BUSY);
+	    }
+
+	  if (!(status & _XABORT_RETRY))
+	    {
+	      if ((status & _XABORT_EXPLICIT)
+			&& _XABORT_CODE (status) == _ABORT_LOCK_BUSY)
+	        {
+		  /* Right now we skip here. Better would be to wait a bit
+		     and retry. This likely needs some spinning.  */
+		  if (*adapt_count != aconf.skip_lock_busy)
+		    *adapt_count = aconf.skip_lock_busy;
+		}
+	      /* Internal abort. There is no chance for retry.
+		 Use the normal locking and next time use lock.
+		 Be careful to avoid writing to the lock.  */
+	      else if (*adapt_count != aconf.skip_lock_internal_abort)
+		*adapt_count = aconf.skip_lock_internal_abort;
+	      break;
+	    }
+	}
+    }
+  else
+    {
+      /* Use a normal lock until the threshold counter runs out.
+	 Lost updates possible.  */
+      (*adapt_count)--;
+    }
+
+  /* Use a normal lock here.  */
+  return LLL_LOCK ((*futex), private);
+}
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/elision-timed.c b/nptl/sysdeps/unix/sysv/linux/x86/elision-timed.c
new file mode 100644
index 0000000000..8825d1287e
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-timed.c
@@ -0,0 +1,26 @@
+/* elision-timed.c: Lock elision timed lock.
+   Copyright (C) 2013 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/x86/elision-trylock.c b/nptl/sysdeps/unix/sysv/linux/x86/elision-trylock.c
new file mode 100644
index 0000000000..2939fc9640
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-trylock.c
@@ -0,0 +1,72 @@
+/* elision-trylock.c: Lock eliding trylock for pthreads.
+   Copyright (C) 2013 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 "hle.h"
+#include <elision-conf.h>
+
+#define aconf __elision_aconf
+
+/* Try to elide a futex trylock. FUTEX is the futex variable. TRY_LOCK is the
+   adaptation counter in the mutex. UPGRADED is != 0 when this is for an
+   automatically upgraded lock.  */
+
+int
+__lll_trylock_elision (int *futex, short *adapt_count)
+{
+  /* Implement POSIX semantics by forbiding nesting
+     trylock. Sorry. After the abort the code is re-executed
+     non transactional and if the lock was already locked
+     return an error.  */
+  _xabort (_ABORT_NESTED_TRYLOCK);
+
+  /* Only try a transaction if it's worth it.  */
+  if (*adapt_count <= 0)
+    {
+      unsigned status;
+
+      if ((status = _xbegin()) == _XBEGIN_STARTED)
+	{
+	  if (*futex == 0)
+	    return 0;
+
+	  /* Lock was busy. Fall back to normal locking.
+	     Could also _xend here but xabort with 0xff code
+	     is more visible in the profiler.  */
+	  _xabort (_ABORT_LOCK_BUSY);
+	}
+
+      if (!(status & _XABORT_RETRY))
+        {
+          /* Internal abort. No chance for retry. For future
+             locks don't try speculation for some time.  */
+          if (*adapt_count != aconf.skip_trylock_internal_abort)
+            *adapt_count = aconf.skip_trylock_internal_abort;
+        }
+      /* Could do some retries here. */
+    }
+  else
+    {
+      /* Lost updates are possible, but harmless.  */
+      (*adapt_count)--;
+    }
+
+  return lll_trylock (*futex);
+}
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/elision-unlock.c b/nptl/sysdeps/unix/sysv/linux/x86/elision-unlock.c
new file mode 100644
index 0000000000..bb13c6b300
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/elision-unlock.c
@@ -0,0 +1,33 @@
+/* elision-unlock.c: Commit an elided pthread lock.
+   Copyright (C) 2013 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"
+#include "hle.h"
+
+int
+__lll_unlock_elision(int *lock, int private)
+{
+  /* When the lock was free we're in a transaction.
+     When you crash here you unlocked a free lock.  */
+  if (*lock == 0)
+    _xend();
+  else
+    lll_unlock ((*lock), private);
+  return 0;
+}
diff --git a/nptl/sysdeps/unix/sysv/linux/x86/hle.h b/nptl/sysdeps/unix/sysv/linux/x86/hle.h
new file mode 100644
index 0000000000..a08f0fa711
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/x86/hle.h
@@ -0,0 +1,75 @@
+/* Shared RTM header. Emulate TSX intrinsics for compilers and assemblers
+   that do not support the intrinsics and instructions yet. */
+#ifndef _HLE_H
+#define _HLE_H 1
+
+#ifdef __ASSEMBLER__
+
+.macro XBEGIN target
+	.byte 0xc7,0xf8
+	.long \target-1f
+1:
+.endm
+
+.macro XEND
+	.byte 0x0f,0x01,0xd5
+.endm
+
+.macro XABORT code
+	.byte 0xc6,0xf8,\code
+.endm
+
+.macro XTEST
+	 .byte 0x0f,0x01,0xd6
+.endm
+
+#endif
+
+/* Official RTM intrinsics interface matching gcc/icc, but works
+   on older gcc compatible compilers and binutils.
+   We should somehow detect if the compiler supports it, because
+   it may be able to generate slightly better code. */
+
+#define _XBEGIN_STARTED		(~0u)
+#define _XABORT_EXPLICIT	(1 << 0)
+#define _XABORT_RETRY		(1 << 1)
+#define _XABORT_CONFLICT	(1 << 2)
+#define _XABORT_CAPACITY	(1 << 3)
+#define _XABORT_DEBUG		(1 << 4)
+#define _XABORT_NESTED		(1 << 5)
+#define _XABORT_CODE(x)		(((x) >> 24) & 0xff)
+
+#define _ABORT_LOCK_BUSY 	0xff
+#define _ABORT_LOCK_IS_LOCKED	0xfe
+#define _ABORT_NESTED_TRYLOCK	0xfd
+
+#ifndef __ASSEMBLER__
+
+#define __force_inline __attribute__((__always_inline__)) inline
+
+static __force_inline int _xbegin(void)
+{
+  int ret = _XBEGIN_STARTED;
+  asm volatile (".byte 0xc7,0xf8 ; .long 0" : "+a" (ret) :: "memory");
+  return ret;
+}
+
+static __force_inline void _xend(void)
+{
+  asm volatile (".byte 0x0f,0x01,0xd5" ::: "memory");
+}
+
+static __force_inline void _xabort(const unsigned int status)
+{
+  asm volatile (".byte 0xc6,0xf8,%P0" :: "i" (status) : "memory");
+}
+
+static __force_inline int _xtest(void)
+{
+  unsigned char out;
+  asm volatile (".byte 0x0f,0x01,0xd6 ; setnz %0" : "=r" (out) :: "memory");
+  return out;
+}
+
+#endif
+#endif
diff --git a/nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h b/nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
index 7a176aec38..35fb01a0de 100644
--- a/nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
+++ b/nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
@@ -427,6 +427,13 @@ LLL_STUB_UNWIND_INFO_END
 		       : "memory", "cx", "cc", "r10", "r11");		      \
      result; })
 
+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)
+
 #define lll_robust_timedlock(futex, timeout, id, private) \
   ({ int result, ignore1, ignore2, ignore3;				      \
      __asm __volatile (LOCK_INSTR "cmpxchgl %1, %4\n\t"			      \
@@ -597,6 +604,22 @@ extern int __lll_timedwait_tid (int *tid, const struct timespec *abstime)
       }									      \
     __result; })
 
+extern int __lll_lock_elision (int *futex, short *adapt_count, int private)
+  attribute_hidden;
+
+extern int __lll_unlock_elision (int *lock, int private)
+  attribute_hidden;
+
+extern int __lll_trylock_elision (int *lock, 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  /* !__ASSEMBLER__ */
 
 #endif	/* lowlevellock.h */