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

   1 /* elision-lock.c: Elided pthread mutex lock.
   2    Copyright (C) 2015-2019 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 <stdio.h>
  20 #include <pthread.h>
  21 #include <pthreadP.h>
  22 #include <lowlevellock.h>
  23 #include <elision-conf.h>
  24 #include "htm.h"
  25
  26 #if !defined(LLL_LOCK) && !defined(EXTRAARG)
  27 /* Make sure the configuration code is always linked in for static
  28    libraries.  */
  29 #include "elision-conf.c"
  30 #endif
  31
  32 #ifndef EXTRAARG
  33 # define EXTRAARG
  34 #endif
  35 #ifndef LLL_LOCK
  36 # define LLL_LOCK(a,b) lll_lock(a,b), 0
  37 #endif
  38
  39 #define aconf __elision_aconf
  40
  41 /* Adaptive lock using transactions.
  42    By default the lock region is run as a transaction, and when it
  43    aborts or the lock is busy the lock adapts itself.  */
  44
  45 int
  46 __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
  47 {
  48   /* adapt_count is accessed concurrently but is just a hint.  Thus,
  49      use atomic accesses but relaxed MO is sufficient.  */
  50   if (atomic_load_relaxed (adapt_count) > 0)
  51     {
  52       goto use_lock;
  53     }
  54
  55   for (int i = aconf.try_tbegin; i > 0; i--)
  56     {
  57       if (__libc_tbegin (0))
  58         {
  59           if (*lock == 0)
  60             return 0;
  61           /* Lock was busy.  Fall back to normal locking.  */
  62           __libc_tabort (_ABORT_LOCK_BUSY);
  63         }
  64       else
  65         {
  66           /* A persistent failure indicates that a retry will probably
  67              result in another failure.  Use normal locking now and
  68              for the next couple of calls.  */
  69           if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
  70             {
  71               if (aconf.skip_lock_internal_abort > 0)
  72                 atomic_store_relaxed (adapt_count,
  73                                       aconf.skip_lock_internal_abort);
  74               goto use_lock;
  75             }
  76         }
  77      }
  78
  79   /* Fall back to locks for a bit if retries have been exhausted */
  80   if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
  81     atomic_store_relaxed (adapt_count,
  82                           aconf.skip_lock_out_of_tbegin_retries);
  83
  84 use_lock:
  85   return LLL_LOCK ((*lock), pshared);
  86 }