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

   1 /* elision-lock.c: Elided pthread mutex lock.
   2    Copyright (C) 2015-2023 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 #ifndef EXTRAARG
  27 # define EXTRAARG
  28 #endif
  29 #ifndef LLL_LOCK
  30 # define LLL_LOCK(a,b) lll_lock(a,b), 0
  31 #endif
  32
  33 #define aconf __elision_aconf
  34
  35 /* Adaptive lock using transactions.
  36    By default the lock region is run as a transaction, and when it
  37    aborts or the lock is busy the lock adapts itself.  */
  38
  39 int
  40 __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
  41 {
  42   /* adapt_count is accessed concurrently but is just a hint.  Thus,
  43      use atomic accesses but relaxed MO is sufficient.  */
  44   if (atomic_load_relaxed (adapt_count) > 0)
  45     {
  46       goto use_lock;
  47     }
  48
  49   for (int i = aconf.try_tbegin; i > 0; i--)
  50     {
  51       if (__libc_tbegin (0))
  52         {
  53           if (*lock == 0)
  54             return 0;
  55           /* Lock was busy.  Fall back to normal locking.  */
  56           __libc_tabort (_ABORT_LOCK_BUSY);
  57         }
  58       else
  59         {
  60           /* A persistent failure indicates that a retry will probably
  61              result in another failure.  Use normal locking now and
  62              for the next couple of calls.  */
  63           if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
  64             {
  65               if (aconf.skip_lock_internal_abort > 0)
  66                 atomic_store_relaxed (adapt_count,
  67                                       aconf.skip_lock_internal_abort);
  68               goto use_lock;
  69             }
  70         }
  71      }
  72
  73   /* Fall back to locks for a bit if retries have been exhausted */
  74   if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
  75     atomic_store_relaxed (adapt_count,
  76                           aconf.skip_lock_out_of_tbegin_retries);
  77
  78 use_lock:
  79   return LLL_LOCK ((*lock), pshared);
  80 }
  81 libc_hidden_def (__lll_lock_elision)