sysdeps/unix/sysv/linux/s390/elision-conf.c

   1 /* Lock elision tunable parameters.
   2    Copyright (C) 2014-2021 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 <elision-conf.h>
  22 #include <unistd.h>
  23 #include <dl-procinfo.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 to not attempt to use elision if a lock used up all retries
  44        without success.  Expressed in number of lock acquisition attempts.  */
  45     .skip_lock_out_of_tbegin_retries = 3,
  46     /* How often we try using elision if there is chance for the transaction
  47        to finish execution (e.g., it wasn't aborted due to the lock being
  48        already acquired.  */
  49     .try_tbegin = 3,
  50     /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock.  */
  51     .skip_trylock_internal_abort = 3,
  52   };
  53
  54 /* Force elision for all new locks.  This is used to decide whether existing
  55    DEFAULT locks should be automatically upgraded to elision in
  56    pthread_mutex_lock().  Disabled for suid programs.  Only used when elision
  57    is available.  */
  58
  59 int __pthread_force_elision attribute_hidden = 0;
  60
  61 #if HAVE_TUNABLES
  62 static inline void
  63 __always_inline
  64 do_set_elision_enable (int32_t elision_enable)
  65 {
  66   /* Enable elision if it's avaliable in hardware. It's not necessary to check
  67      if __libc_enable_secure isn't enabled since elision_enable will be set
  68      according to the default, which is disabled.  */
  69   if (elision_enable == 1)
  70     __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
  71 }
  72
  73 /* The pthread->elision_enable tunable is 0 or 1 indicating that elision
  74    should be disabled or enabled respectively.  The feature will only be used
  75    if it's supported by the hardware.  */
  76
  77 void
  78 TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
  79 {
  80   int32_t elision_enable = (int32_t) valp->numval;
  81   do_set_elision_enable (elision_enable);
  82 }
  83
  84 #define TUNABLE_CALLBACK_FNDECL(__name, __type)                 \
  85 static inline void                                              \
  86 __always_inline                                                 \
  87 do_set_elision_ ## __name (__type value)                        \
  88 {                                                               \
  89   __elision_aconf.__name = value;                               \
  90 }                                                               \
  91 void                                                            \
  92 TUNABLE_CALLBACK (set_elision_ ## __name) (tunable_val_t *valp) \
  93 {                                                               \
  94   __type value = (__type) (valp)->numval;                       \
  95   do_set_elision_ ## __name (value);                            \
  96 }
  97
  98 TUNABLE_CALLBACK_FNDECL (skip_lock_busy, int32_t);
  99 TUNABLE_CALLBACK_FNDECL (skip_lock_internal_abort, int32_t);
 100 TUNABLE_CALLBACK_FNDECL (skip_lock_out_of_tbegin_retries, int32_t);
 101 TUNABLE_CALLBACK_FNDECL (try_tbegin, int32_t);
 102 TUNABLE_CALLBACK_FNDECL (skip_trylock_internal_abort, int32_t);
 103 #endif
 104
 105 /* Initialize elison.  */
 106
 107 static void
 108 elision_init (int argc __attribute__ ((unused)),
 109               char **argv  __attribute__ ((unused)),
 110               char **environ)
 111 {
 112 #if HAVE_TUNABLES
 113   /* Elision depends on tunables and must be explicitly turned on by setting
 114      the appropriate tunable on a supported platform.  */
 115
 116   TUNABLE_GET (enable, int32_t,
 117                TUNABLE_CALLBACK (set_elision_enable));
 118   TUNABLE_GET (skip_lock_busy, int32_t,
 119                TUNABLE_CALLBACK (set_elision_skip_lock_busy));
 120   TUNABLE_GET (skip_lock_internal_abort, int32_t,
 121                TUNABLE_CALLBACK (set_elision_skip_lock_internal_abort));
 122   TUNABLE_GET (skip_lock_after_retries, int32_t,
 123                TUNABLE_CALLBACK (set_elision_skip_lock_out_of_tbegin_retries));
 124   TUNABLE_GET (tries, int32_t,
 125                TUNABLE_CALLBACK (set_elision_try_tbegin));
 126   TUNABLE_GET (skip_trylock_internal_abort, int32_t,
 127                TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
 128 #endif
 129
 130   if (!__pthread_force_elision)
 131     __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks.  */
 132 }
 133
 134 #ifdef SHARED
 135 # define INIT_SECTION ".init_array"
 136 # define MAYBE_CONST
 137 #else
 138 # define INIT_SECTION ".preinit_array"
 139 # define MAYBE_CONST const
 140 #endif
 141
 142 void (*MAYBE_CONST __pthread_init_array []) (int, char **, char **)
 143   __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
 144 {
 145   &elision_init
 146 };