ports/sysdeps/tile/nptl/pthread_spin_lock.c

   1 /* Copyright (C) 2011-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
   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 "pthreadP.h"
  20 #include <arch/spr_def.h>
  21 #include <atomic.h>
  22
  23 /* Bound point for bounded exponential backoff */
  24 #define BACKOFF_MAX 2048
  25
  26 /* Initial cycle delay for exponential backoff */
  27 #define BACKOFF_START 32
  28
  29 #ifdef __tilegx__
  30 /* Use cmpexch() after the initial fast-path exch to avoid
  31    invalidating the cache line of the lock holder.  */
  32 # define TNS(p) atomic_exchange_acq((p), 1)
  33 # define CMPTNS(p) atomic_compare_and_exchange_val_acq((p), 1, 0)
  34 #else
  35 # define TNS(p) __insn_tns(p)
  36 # define CMPTNS(p) __insn_tns(p)
  37 # define SPR_CYCLE SPR_CYCLE_LOW   /* The low 32 bits are sufficient. */
  38 #endif
  39
  40 int
  41 pthread_spin_lock (pthread_spinlock_t *lock)
  42 {
  43   if (__builtin_expect (TNS (lock) != 0, 0))
  44     {
  45       unsigned int backoff = BACKOFF_START;
  46       while (CMPTNS (lock) != 0)
  47         {
  48           unsigned int start = __insn_mfspr (SPR_CYCLE);
  49           while (__insn_mfspr (SPR_CYCLE) - start < backoff)
  50             ;
  51           if (backoff < BACKOFF_MAX)
  52             backoff *= 2;
  53         }
  54     }
  55   return 0;
  56 }