module/spl/spl-mutex.c

   1 /*
   2  *  This file is part of the SPL: Solaris Porting Layer.
   3  *
   4  *  Copyright (c) 2009 Lawrence Livermore National Security, LLC.
   5  *  Produced at Lawrence Livermore National Laboratory
   6  *  Written by:
   7  *          Brian Behlendorf <behlendorf1@llnl.gov>,
   8  *          Herb Wartens <wartens2@llnl.gov>,
   9  *          Jim Garlick <garlick@llnl.gov>
  10  *  UCRL-CODE-235197
  11  *
  12  *  This is free software; you can redistribute it and/or modify it
  13  *  under the terms of the GNU General Public License as published by
  14  *  the Free Software Foundation; either version 2 of the License, or
  15  *  (at your option) any later version.
  16  *
  17  *  This is distributed in the hope that it will be useful, but WITHOUT
  18  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  19  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  20  *  for more details.
  21  *
  22  *  You should have received a copy of the GNU General Public License along
  23  *  with this program; if not, write to the Free Software Foundation, Inc.,
  24  *  51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA.
  25  */
  26
  27 #include <sys/mutex.h>
  28
  29 #ifdef DEBUG_SUBSYSTEM
  30 #undef DEBUG_SUBSYSTEM
  31 #endif
  32
  33 #define DEBUG_SUBSYSTEM S_MUTEX
  34
  35 /*
  36  * While a standard mutex implementation has been available in the kernel
  37  * for quite some time.  It was not until 2.6.29 and latter kernels that
  38  * adaptive mutexs were embraced and integrated with the scheduler.  This
  39  * brought a significant performance improvement, but just as importantly
  40  * it added a lock owner to the generic mutex outside CONFIG_DEBUG_MUTEXES
  41  * builds.  This is critical for correctly supporting the mutex_owner()
  42  * Solaris primitive.  When the owner is available we use a pure Linux
  43  * mutex implementation.  When the owner is not available we still use
  44  * Linux mutexs as a base but also reserve space for an owner field right
  45  * after the mutex structure.
  46  *
  47  * In the case when HAVE_MUTEX_OWNER is not defined your code may
  48  * still me able to leverage adaptive mutexs.  As long as the task_curr()
  49  * symbol is exported this code will provide a poor mans adaptive mutex
  50  * implementation.  However, this is not required and if the symbol is
  51  * unavailable we provide a standard mutex.
  52  */
  53
  54 #ifndef HAVE_MUTEX_OWNER
  55 #ifdef HAVE_TASK_CURR
  56 /*
  57  * mutex_spin_max = { 0, -1, 1-MAX_INT }
  58  *  0:         Never spin when trying to acquire lock
  59  * -1:         Spin until acquired or holder yields without dropping lock
  60  *  1-MAX_INT: Spin for N attempts before sleeping for lock
  61  */
  62 int mutex_spin_max = 0;
  63 module_param(mutex_spin_max, int, 0644);
  64 MODULE_PARM_DESC(mutex_spin_max, "Spin a maximum of N times to acquire lock");
  65
  66 int
  67 spl_mutex_spin_max(void)
  68 {
  69         return mutex_spin_max;
  70 }
  71 EXPORT_SYMBOL(spl_mutex_spin_max);
  72
  73 #endif /* HAVE_TASK_CURR */
  74 #endif /* !HAVE_MUTEX_OWNER */
  75
  76 int spl_mutex_init(void) { return 0; }
  77 void spl_mutex_fini(void) { }