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

   1 /* elision-conf.c: Lock elision tunable parameters.
   2    Copyright (C) 2015-2017 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    <http://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 /* Reasonable initial tuning values, may be revised in the future.
  26    This is a conservative initial value.  */
  27
  28 struct elision_config __elision_aconf =
  29   {
  30     /* How many times to use a non-transactional lock after a transactional
  31        failure has occurred because the lock is already acquired.  Expressed
  32        in number of lock acquisition attempts.  */
  33     .skip_lock_busy = 3,
  34     /* How often to not attempt to use elision if a transaction aborted due
  35        to reasons other than other threads' memory accesses.  Expressed in
  36        number of lock acquisition attempts.  */
  37     .skip_lock_internal_abort = 3,
  38     /* How often to not attempt to use elision if a lock used up all retries
  39        without success.  Expressed in number of lock acquisition attempts.  */
  40     .skip_lock_out_of_tbegin_retries = 3,
  41     /* How often we retry using elision if there is chance for the transaction
  42        to finish execution (e.g., it wasn't aborted due to the lock being
  43        already acquired.  */
  44     .try_tbegin = 3,
  45     /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock.  */
  46     .skip_trylock_internal_abort = 3,
  47   };
  48
  49 /* Force elision for all new locks.  This is used to decide whether existing
  50    DEFAULT locks should be automatically use elision in pthread_mutex_lock().
  51    Disabled for suid programs.  Only used when elision is available.  */
  52
  53 int __pthread_force_elision attribute_hidden;
  54
  55 /* Initialize elision.  */
  56
  57 static void
  58 elision_init (int argc __attribute__ ((unused)),
  59               char **argv  __attribute__ ((unused)),
  60               char **environ)
  61 {
  62 #ifdef ENABLE_LOCK_ELISION
  63   int elision_available = (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
  64   __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
  65 #endif
  66   if (!__pthread_force_elision)
  67     /* Disable elision on rwlocks.  */
  68     __elision_aconf.try_tbegin = 0;
  69 }
  70
  71 #ifdef SHARED
  72 # define INIT_SECTION ".init_array"
  73 # define MAYBE_CONST
  74 #else
  75 # define INIT_SECTION ".preinit_array"
  76 # define MAYBE_CONST const
  77 #endif
  78
  79 void (*MAYBE_CONST __pthread_init_array []) (int, char **, char **)
  80   __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
  81 {
  82   &elision_init
  83 };