commit e8c659d74e011346785355eeef03b7fb6f533c61

Author: Andi Kleen <ak@linux.intel.com>

Date:   Sat Dec 22 01:03:04 2012 -0800

    Add elision to pthread_mutex_{try,timed,un}lock

    Add elision paths to the basic mutex locks.

    The normal path has a check for RTM and upgrades the lock

    to RTM when available. Trylocks cannot automatically upgrade,

    so they check for elision every time.

    We use a 4 byte value in the mutex to store the lock

    elision adaptation state. This is separate from the adaptive

    spin state and uses a separate field.

    Condition variables currently do not support elision.

    Recursive mutexes and condition variables may be supported at some point,

    but are not in the current implementation. Also "trylock" will

    not automatically enable elision unless some other lock call

    has been already called on the lock.

    This version does not use IFUNC, so it means every lock has one

    additional check for elision. Benchmarking showed the overhead

    to be negligible.

Index: glibc-2.17-c758a686/nptl/pthreadP.h

===================================================================

--- glibc-2.17-c758a686.orig/nptl/pthreadP.h

+++ glibc-2.17-c758a686/nptl/pthreadP.h

@@ -110,8 +110,10 @@ enum

 #define PTHREAD_MUTEX_TYPE(m) \

   ((m)->__data.__kind & 127)

+/* Don't include NO_ELISION, as that type is always the same

+   as the underlying lock type.  */

 #define PTHREAD_MUTEX_TYPE_ELISION(m) \

-  ((m)->__data.__kind & (127|PTHREAD_MUTEX_ELISION_FLAGS_NP))

+  ((m)->__data.__kind & (127|PTHREAD_MUTEX_ELISION_NP))

 #if LLL_PRIVATE == 0 && LLL_SHARED == 128

 # define PTHREAD_MUTEX_PSHARED(m) \

Index: glibc-2.17-c758a686/nptl/pthread_mutex_lock.c

===================================================================

--- glibc-2.17-c758a686.orig/nptl/pthread_mutex_lock.c

+++ glibc-2.17-c758a686/nptl/pthread_mutex_lock.c

@@ -25,6 +25,14 @@

 #include <lowlevellock.h>

 #include <stap-probe.h>

+#ifndef lll_lock_elision

+#define lll_lock_elision(lock, try_lock, private)	({ \

+      lll_lock (lock, private); 0; })

+#endif

+

+#ifndef lll_trylock_elision

+#define lll_trylock_elision(a,t) lll_trylock(a)

+#endif

 #ifndef LLL_MUTEX_LOCK

 # define LLL_MUTEX_LOCK(mutex) \

@@ -34,39 +42,60 @@

 # define LLL_ROBUST_MUTEX_LOCK(mutex, id) \

   lll_robust_lock ((mutex)->__data.__lock, id, \

 		   PTHREAD_ROBUST_MUTEX_PSHARED (mutex))

+# define LLL_MUTEX_LOCK_ELISION(mutex) \

+  lll_lock_elision ((mutex)->__data.__lock, (mutex)->__data.__elision, \

+		   PTHREAD_MUTEX_PSHARED (mutex))

+# define LLL_MUTEX_TRYLOCK_ELISION(mutex) \

+  lll_trylock_elision((mutex)->__data.__lock, (mutex)->__data.__elision, \

+		   PTHREAD_MUTEX_PSHARED (mutex))

 #endif

+#ifndef FORCE_ELISION

+#define FORCE_ELISION(m, s)

+#endif

 static int __pthread_mutex_lock_full (pthread_mutex_t *mutex)

      __attribute_noinline__;

-

 int

 __pthread_mutex_lock (mutex)

      pthread_mutex_t *mutex;

 {

   assert (sizeof (mutex->__size) >= sizeof (mutex->__data));

-  unsigned int type = PTHREAD_MUTEX_TYPE (mutex);

+  unsigned int type = PTHREAD_MUTEX_TYPE_ELISION (mutex);

   LIBC_PROBE (mutex_entry, 1, mutex);

-  if (__builtin_expect (type & ~PTHREAD_MUTEX_KIND_MASK_NP, 0))

+  if (__builtin_expect (type & ~(PTHREAD_MUTEX_KIND_MASK_NP

+				 | PTHREAD_MUTEX_ELISION_FLAGS_NP), 0))

     return __pthread_mutex_lock_full (mutex);

-  pid_t id = THREAD_GETMEM (THREAD_SELF, tid);

-

-  if (__builtin_expect (type, PTHREAD_MUTEX_TIMED_NP)

-      == PTHREAD_MUTEX_TIMED_NP)

+  if (__builtin_expect (type == PTHREAD_MUTEX_TIMED_NP, 1))

     {

+      FORCE_ELISION (mutex, goto elision);

     simple:

       /* Normal mutex.  */

       LLL_MUTEX_LOCK (mutex);

       assert (mutex->__data.__owner == 0);

     }

-  else if (__builtin_expect (type == PTHREAD_MUTEX_RECURSIVE_NP, 1))

+#ifdef HAVE_ELISION

+  else if (__builtin_expect (type == PTHREAD_MUTEX_TIMED_ELISION_NP, 1))

+    {

+  elision: __attribute__((unused))

+      /* This case can never happen on a system without elision,

+         as the mutex type initialization functions will not

+	 allow to set the elision flags.  */

+      /* Don't record owner or users for elision case. This is a

+         tail call.  */

+      return LLL_MUTEX_LOCK_ELISION (mutex);

+    }

+#endif

+  else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)

+			     == PTHREAD_MUTEX_RECURSIVE_NP, 1))

     {

       /* Recursive mutex.  */

+      pid_t id = THREAD_GETMEM (THREAD_SELF, tid);

       /* Check whether we already hold the mutex.  */

       if (mutex->__data.__owner == id)

@@ -87,7 +116,8 @@ __pthread_mutex_lock (mutex)

       assert (mutex->__data.__owner == 0);

       mutex->__data.__count = 1;

     }

-  else if (__builtin_expect (type == PTHREAD_MUTEX_ADAPTIVE_NP, 1))

+  else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)

+			  == PTHREAD_MUTEX_ADAPTIVE_NP, 1))

     {

       if (! __is_smp)

 	goto simple;

@@ -117,13 +147,16 @@ __pthread_mutex_lock (mutex)

     }

   else

     {

-      assert (type == PTHREAD_MUTEX_ERRORCHECK_NP);

+      pid_t id = THREAD_GETMEM (THREAD_SELF, tid);

+      assert (PTHREAD_MUTEX_TYPE (mutex) == PTHREAD_MUTEX_ERRORCHECK_NP);

       /* Check whether we already hold the mutex.  */

       if (__builtin_expect (mutex->__data.__owner == id, 0))

 	return EDEADLK;

       goto simple;

     }

+  pid_t id = THREAD_GETMEM (THREAD_SELF, tid);

+

   /* Record the ownership.  */

   mutex->__data.__owner = id;

 #ifndef NO_INCR

Index: glibc-2.17-c758a686/nptl/pthread_mutex_timedlock.c

===================================================================

--- glibc-2.17-c758a686.orig/nptl/pthread_mutex_timedlock.c

+++ glibc-2.17-c758a686/nptl/pthread_mutex_timedlock.c

@@ -25,6 +25,17 @@

 #include <stap-probe.h>

+#ifndef lll_timedlock_elision

+#define lll_timedlock_elision(a,dummy,b,c) lll_timedlock(a, b, c)

+#endif

+

+#ifndef lll_trylock_elision

+#define lll_trylock_elision(a,t) lll_trylock(a)

+#endif

+

+#ifndef FORCE_ELISION

+#define FORCE_ELISION(m, s)

+#endif

 int

 pthread_mutex_timedlock (mutex, abstime)

@@ -40,10 +51,11 @@ pthread_mutex_timedlock (mutex, abstime)

   /* We must not check ABSTIME here.  If the thread does not block

      abstime must not be checked for a valid value.  */

-  switch (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex),

+  switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),

 			    PTHREAD_MUTEX_TIMED_NP))

     {

       /* Recursive mutex.  */

+    case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:

     case PTHREAD_MUTEX_RECURSIVE_NP:

       /* Check whether we already hold the mutex.  */

       if (mutex->__data.__owner == id)

@@ -78,12 +90,22 @@ pthread_mutex_timedlock (mutex, abstime)

       /* FALLTHROUGH */

     case PTHREAD_MUTEX_TIMED_NP:

+      FORCE_ELISION (mutex, goto elision);

     simple:

       /* Normal mutex.  */

       result = lll_timedlock (mutex->__data.__lock, abstime,

 			      PTHREAD_MUTEX_PSHARED (mutex));

       break;

+    case PTHREAD_MUTEX_TIMED_ELISION_NP:

+    elision: __attribute__((unused))

+      /* Don't record ownership */

+      return lll_timedlock_elision (mutex->__data.__lock,

+				    mutex->__data.__spins,

+				    abstime,

+				    PTHREAD_MUTEX_PSHARED (mutex));

+

+

     case PTHREAD_MUTEX_ADAPTIVE_NP:

       if (! __is_smp)

 	goto simple;

Index: glibc-2.17-c758a686/nptl/pthread_mutex_trylock.c

===================================================================

--- glibc-2.17-c758a686.orig/nptl/pthread_mutex_trylock.c

+++ glibc-2.17-c758a686/nptl/pthread_mutex_trylock.c

@@ -22,6 +22,16 @@

 #include "pthreadP.h"

 #include <lowlevellock.h>

+#ifndef lll_trylock_elision

+#define lll_trylock_elision(a,t) lll_trylock(a)

+#endif

+

+#ifndef DO_ELISION

+#define DO_ELISION(m) 0

+#endif

+

+/* We don't force elision in trylock, because this can lead to inconsistent

+   lock state if the lock was actually busy. */

 int

 __pthread_mutex_trylock (mutex)

@@ -30,10 +40,11 @@ __pthread_mutex_trylock (mutex)

   int oldval;

   pid_t id = THREAD_GETMEM (THREAD_SELF, tid);

-  switch (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex),

+  switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),

 			    PTHREAD_MUTEX_TIMED_NP))

     {

       /* Recursive mutex.  */

+    case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:

     case PTHREAD_MUTEX_RECURSIVE_NP:

       /* Check whether we already hold the mutex.  */

       if (mutex->__data.__owner == id)

@@ -57,10 +68,20 @@ __pthread_mutex_trylock (mutex)

 	}

       break;

-    case PTHREAD_MUTEX_ERRORCHECK_NP:

+    case PTHREAD_MUTEX_TIMED_ELISION_NP:

+    elision:

+      if (lll_trylock_elision (mutex->__data.__lock,

+			       mutex->__data.__elision) != 0)

+        break;

+      /* Don't record the ownership. */

+      return 0;

+

     case PTHREAD_MUTEX_TIMED_NP:

+      if (DO_ELISION (mutex))

+	goto elision;

+      /*FALL THROUGH*/

     case PTHREAD_MUTEX_ADAPTIVE_NP:

-      /* Normal mutex.  */

+    case PTHREAD_MUTEX_ERRORCHECK_NP:

       if (lll_trylock (mutex->__data.__lock) != 0)

 	break;

@@ -378,4 +399,9 @@ __pthread_mutex_trylock (mutex)

   return EBUSY;

 }

+

+#ifndef __pthread_mutex_trylock

+#ifndef pthread_mutex_trylock

 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)

+#endif

+#endif

Index: glibc-2.17-c758a686/nptl/pthread_mutex_unlock.c

===================================================================

--- glibc-2.17-c758a686.orig/nptl/pthread_mutex_unlock.c

+++ glibc-2.17-c758a686/nptl/pthread_mutex_unlock.c

@@ -23,6 +23,10 @@

 #include <lowlevellock.h>

 #include <stap-probe.h>

+#ifndef lll_unlock_elision

+#define lll_unlock_elision(a,b) ({ lll_unlock (a,b); 0; })

+#endif

+

 static int

 internal_function

 __pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr)

@@ -34,8 +38,9 @@ __pthread_mutex_unlock_usercnt (mutex, d

      pthread_mutex_t *mutex;

      int decr;

 {

-  int type = PTHREAD_MUTEX_TYPE (mutex);

-  if (__builtin_expect (type & ~PTHREAD_MUTEX_KIND_MASK_NP, 0))

+  int type = PTHREAD_MUTEX_TYPE_ELISION (mutex);

+  if (__builtin_expect (type &

+		~(PTHREAD_MUTEX_KIND_MASK_NP|PTHREAD_MUTEX_ELISION_FLAGS_NP), 0))

     return __pthread_mutex_unlock_full (mutex, decr);

   if (__builtin_expect (type, PTHREAD_MUTEX_TIMED_NP)

@@ -55,7 +60,14 @@ __pthread_mutex_unlock_usercnt (mutex, d

       return 0;

     }

-  else if (__builtin_expect (type == PTHREAD_MUTEX_RECURSIVE_NP, 1))

+  else if (__builtin_expect (type == PTHREAD_MUTEX_TIMED_ELISION_NP, 1))

+    {

+      /* Don't reset the owner/users fields for elision.  */

+      return lll_unlock_elision (mutex->__data.__lock,

+				      PTHREAD_MUTEX_PSHARED (mutex));

+    }

+  else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)

+			      == PTHREAD_MUTEX_RECURSIVE_NP, 1))

     {

       /* Recursive mutex.  */

       if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))

@@ -66,7 +78,8 @@ __pthread_mutex_unlock_usercnt (mutex, d

 	return 0;

       goto normal;

     }

-  else if (__builtin_expect (type == PTHREAD_MUTEX_ADAPTIVE_NP, 1))

+  else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)

+			      == PTHREAD_MUTEX_ADAPTIVE_NP, 1))

     goto normal;

   else

     {

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/pthread_mutex_cond_lock.c

===================================================================

--- glibc-2.17-c758a686.orig/nptl/sysdeps/unix/sysv/linux/pthread_mutex_cond_lock.c

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/pthread_mutex_cond_lock.c

@@ -2,8 +2,15 @@

 #define LLL_MUTEX_LOCK(mutex) \

   lll_cond_lock ((mutex)->__data.__lock, PTHREAD_MUTEX_PSHARED (mutex))

+

+/* Not actually elided so far. Needed? */

+#define LLL_MUTEX_LOCK_ELISION(mutex)  \

+  ({ lll_cond_lock ((mutex)->__data.__lock, PTHREAD_MUTEX_PSHARED (mutex)); 0; })

+

 #define LLL_MUTEX_TRYLOCK(mutex) \

   lll_cond_trylock ((mutex)->__data.__lock)

+#define LLL_MUTEX_TRYLOCK_ELISION(mutex) LLL_MUTEX_TRYLOCK(mutex)

+

 #define LLL_ROBUST_MUTEX_LOCK(mutex, id) \

   lll_robust_cond_lock ((mutex)->__data.__lock, id, \

 			PTHREAD_ROBUST_MUTEX_PSHARED (mutex))

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/bits/pthreadtypes.h

===================================================================

--- glibc-2.17-c758a686.orig/nptl/sysdeps/unix/sysv/linux/x86/bits/pthreadtypes.h

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/bits/pthreadtypes.h

@@ -101,14 +101,23 @@ typedef union

        binary compatibility.  */

     int __kind;

 #ifdef __x86_64__

-    int __spins;

+    short __spins;

+    short __elision;

     __pthread_list_t __list;

 # define __PTHREAD_MUTEX_HAVE_PREV	1

+# define __PTHREAD_MUTEX_HAVE_ELISION   1

 #else

     unsigned int __nusers;

     __extension__ union

     {

-      int __spins;

+      struct

+      {

+        short __espins;

+	short __elision;

+# define __spins d.__espins

+# define __elision d.__elision

+# define __PTHREAD_MUTEX_HAVE_ELISION   2

+      } d;

       __pthread_slist_t __list;

     };

 #endif

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/elision-trylock.c

===================================================================

--- glibc-2.17-c758a686.orig/nptl/sysdeps/unix/sysv/linux/x86/elision-trylock.c

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/elision-trylock.c

@@ -24,9 +24,8 @@

 #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.  */

+/* 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)

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/force-elision.h

===================================================================

--- /dev/null

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/force-elision.h

@@ -0,0 +1,31 @@

+/* force-elision.h: Automatic enabling of elision for mutexes

+   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/>. */

+

+/* 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;								\

+    }

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c

===================================================================

--- /dev/null

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c

@@ -0,0 +1,21 @@

+/* 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/>. */

+

+/* The cond lock is not actually elided yet, but we still need to handle

+   already elided locks.  */

+#include <elision-conf.h>

+#include "sysdeps/unix/sysv/linux/pthread_mutex_cond_lock.c"

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c

===================================================================

--- /dev/null

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c

@@ -0,0 +1,21 @@

+/* Elided version of pthread_mutex_lock.

+   Copyright (C) 2011, 2012, 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 <elision-conf.h>

+#include "force-elision.h"

+

+#include "nptl/pthread_mutex_lock.c"

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c

===================================================================

--- /dev/null

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c

@@ -0,0 +1,20 @@

+/* Elided version of pthread_mutex_timedlock.

+   Copyright (C) 2011, 2012, 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 <elision-conf.h>

+#include "force-elision.h"

+#include "nptl/pthread_mutex_timedlock.c"

Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_trylock.c

===================================================================

--- /dev/null

+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/x86/pthread_mutex_trylock.c

@@ -0,0 +1,21 @@

+/* Elided version of pthread_mutex_trylock.

+   Copyright (C) 2011, 2012, 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 <elision-conf.h>

+#include "force-elision.h"

+

+#include "nptl/pthread_mutex_trylock.c"