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

   1 /* elision-conf.c: Lock elision tunable parameters.
   2    Copyright (C) 2013-2014 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 <init-arch.h>
  22 #include <elision-conf.h>
  23 #include <unistd.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 often to not attempt to use elision if a transaction aborted
  31        because the lock is already acquired.  Expressed in number of lock
  32        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 we retry using elision if there is chance for the transaction
  39        to finish execution (e.g., it wasn't aborted due to the lock being
  40        already acquired.  */
  41     .retry_try_xbegin = 3,
  42     /* Same as SKIP_LOCK_INTERNAL_ABORT but for trylock.  */
  43     .skip_trylock_internal_abort = 3,
  44   };
  45
  46 /* Set when the CPU supports elision.  When false elision is never attempted.
  47  */
  48
  49 int __elision_available attribute_hidden;
  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;
  57
  58 /* Initialize elison.  */
  59
  60 static void
  61 elision_init (int argc __attribute__ ((unused)),
  62               char **argv  __attribute__ ((unused)),
  63               char **envp)
  64 {
  65   __elision_available = HAS_RTM;
  66 #ifdef ENABLE_LOCK_ELISION
  67   __pthread_force_elision = __libc_enable_secure ? 0 : __elision_available;
  68 #endif
  69   if (!HAS_RTM)
  70     __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */
  71 }
  72
  73 #ifdef SHARED
  74 # define INIT_SECTION ".init_array"
  75 #else
  76 # define INIT_SECTION ".preinit_array"
  77 #endif
  78
  79 void (*const __pthread_init_array []) (int, char **, char **)
  80   __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
  81 {
  82   &elision_init
  83 };