sysdeps/unix/sysv/linux/x86/elision-conf.c

   1 /* elision-conf.c: Lock elision tunable parameters.
   2    Copyright (C) 2013-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include "config.h"
  20 #include <pthreadP.h>
  21 #include <init-arch.h>
  22 #include <elision-conf.h>
  23 #include <unistd.h>
  24
  25 #if HAVE_TUNABLES
  26 # define TUNABLE_NAMESPACE elision
  27 #endif
  28 #include <elf/dl-tunables.h>
  29
  30 /* Reasonable initial tuning values, may be revised in the future.
  31    This is a conservative initial value.  */
  32
  33 struct elision_config __elision_aconf =
  34   {
  35     /* How often to not attempt to use elision if a transaction aborted
  36        because the lock is already acquired.  Expressed in number of lock
  37        acquisition attempts.  */
  38     .skip_lock_busy = 3,
  39     /* How often to not attempt to use elision if a transaction aborted due
  40        to reasons other than other threads' memory accesses.  Expressed in
  41        number of lock acquisition attempts.  */
  42     .skip_lock_internal_abort = 3,
  43     /* How often we retry using elision if there is chance for the transaction
  44        to finish execution (e.g., it wasn't aborted due to the lock being
  45        already acquired.  */
  46     .retry_try_xbegin = 3,
  47     /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock.  */
  48     .skip_trylock_internal_abort = 3,
  49   };
  50
  51 /* Force elision for all new locks.  This is used to decide whether existing
  52    DEFAULT locks should be automatically upgraded to elision in
  53    pthread_mutex_lock().  Disabled for suid programs.  Only used when elision
  54    is available.  */
  55
  56 int __pthread_force_elision attribute_hidden = 0;
  57
  58 #if HAVE_TUNABLES
  59 static __always_inline void
  60 do_set_elision_enable (int32_t elision_enable)
  61 {
  62   /* Enable elision if it's avaliable in hardware. It's not necessary to check
  63      if __libc_enable_secure isn't enabled since elision_enable will be set
  64      according to the default, which is disabled.  */
  65   if (elision_enable == 1)
  66     __pthread_force_elision = HAS_CPU_FEATURE (RTM) ? 1 : 0;
  67 }
  68
  69 /* The pthread->elision_enable tunable is 0 or 1 indicating that elision
  70    should be disabled or enabled respectively.  The feature will only be used
  71    if it's supported by the hardware.  */
  72
  73 void
  74 TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
  75 {
  76   int32_t elision_enable = (int32_t) valp->numval;
  77   do_set_elision_enable (elision_enable);
  78 }
  79
  80 #define TUNABLE_CALLBACK_FNDECL(__name, __type)                 \
  81 static __always_inline void                                     \
  82 do_set_elision_ ## __name (__type value)                        \
  83 {                                                               \
  84   __elision_aconf.__name = value;                               \
  85 }                                                               \
  86 void                                                            \
  87 TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
  88 {                                                               \
  89   __type value = (__type) (valp)->numval;                       \
  90   do_set_elision_ ## __name (value);                            \
  91 }
  92
  93 TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
  94 TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
  95 TUNABLE_CALLBACK_FNDECL (retry_try_xbegin, int32_t);
  96 TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
  97 #endif
  98
  99 /* Initialize elision.  */
 100
 101 static void
 102 elision_init (int argc __attribute__ ((unused)),
 103               char **argv  __attribute__ ((unused)),
 104               char **environ)
 105 {
 106 #if HAVE_TUNABLES
 107   /* Elision depends on tunables and must be explicitly turned on by setting
 108      the appropriate tunable on a supported platform.  */
 109
 110   TUNABLE_GET (enable, int32_t,
 111                TUNABLE_CALLBACK (set_elision_enable));
 112   TUNABLE_GET (skip_lock_busy, int32_t,
 113                TUNABLE_CALLBACK (set_elision_skip_lock_busy));
 114   TUNABLE_GET (skip_lock_internal_abort, int32_t,
 115                TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
 116   TUNABLE_GET (tries, int32_t,
 117                TUNABLE_CALLBACK (set_elision_retry_try_xbegin));
 118   TUNABLE_GET (skip_trylock_internal_abort, int32_t,
 119                TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
 120 #endif
 121
 122   if (!__pthread_force_elision)
 123     __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks.  */
 124 }
 125
 126 #ifdef SHARED
 127 # define INIT_SECTION ".init_array"
 128 #else
 129 # define INIT_SECTION ".preinit_array"
 130 #endif
 131
 132 void (*const __pthread_init_array []) (int, char **, char **)
 133   __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
 134 {
 135   &elision_init
 136 };