LXR linux/include/linux/rcu_node

   1/*
   2 * RCU node combining tree definitions.  These are used to compute
   3 * global attributes while avoiding common-case global contention.  A key
   4 * property that these computations rely on is a tournament-style approach
   5 * where only one of the tasks contending a lower level in the tree need
   6 * advance to the next higher level.  If properly configured, this allows
   7 * unlimited scalability while maintaining a constant level of contention
   8 * on the root node.
   9 *
  10 * This seemingly RCU-private file must be available to SRCU users
  11 * because the size of the TREE SRCU srcu_struct structure depends
  12 * on these definitions.
  13 *
  14 * This program is free software; you can redistribute it and/or modify
  15 * it under the terms of the GNU General Public License as published by
  16 * the Free Software Foundation; either version 2 of the License, or
  17 * (at your option) any later version.
  18 *
  19 * This program is distributed in the hope that it will be useful,
  20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22 * GNU General Public License for more details.
  23 *
  24 * You should have received a copy of the GNU General Public License
  25 * along with this program; if not, you can access it online at
  26 * http://www.gnu.org/licenses/gpl-2.0.html.
  27 *
  28 * Copyright IBM Corporation, 2017
  29 *
  30 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  31 */
  32
  33#ifndef __LINUX_RCU_NODE_TREE_H
  34#define __LINUX_RCU_NODE_TREE_H
  35
  36/*
  37 * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
  38 * CONFIG_RCU_FANOUT_LEAF.
  39 * In theory, it should be possible to add more levels straightforwardly.
  40 * In practice, this did work well going from three levels to four.
  41 * Of course, your mileage may vary.
  42 */
  43
  44#ifdef CONFIG_RCU_FANOUT
  45#define RCU_FANOUT CONFIG_RCU_FANOUT
  46#else /* #ifdef CONFIG_RCU_FANOUT */
  47# ifdef CONFIG_64BIT
  48# define RCU_FANOUT 64
  49# else
  50# define RCU_FANOUT 32
  51# endif
  52#endif /* #else #ifdef CONFIG_RCU_FANOUT */
  53
  54#ifdef CONFIG_RCU_FANOUT_LEAF
  55#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
  56#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
  57#define RCU_FANOUT_LEAF 16
  58#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
  59
  60#define RCU_FANOUT_1          (RCU_FANOUT_LEAF)
  61#define RCU_FANOUT_2          (RCU_FANOUT_1 * RCU_FANOUT)
  62#define RCU_FANOUT_3          (RCU_FANOUT_2 * RCU_FANOUT)
  63#define RCU_FANOUT_4          (RCU_FANOUT_3 * RCU_FANOUT)
  64
  65#if NR_CPUS <= RCU_FANOUT_1
  66#  define RCU_NUM_LVLS        1
  67#  define NUM_RCU_LVL_0       1
  68#  define NUM_RCU_NODES       NUM_RCU_LVL_0
  69#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0 }
  70#  define RCU_NODE_NAME_INIT  { "rcu_node_0" }
  71#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0" }
  72#elif NR_CPUS <= RCU_FANOUT_2
  73#  define RCU_NUM_LVLS        2
  74#  define NUM_RCU_LVL_0       1
  75#  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
  76#  define NUM_RCU_NODES       (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
  77#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
  78#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1" }
  79#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1" }
  80#elif NR_CPUS <= RCU_FANOUT_3
  81#  define RCU_NUM_LVLS        3
  82#  define NUM_RCU_LVL_0       1
  83#  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
  84#  define NUM_RCU_LVL_2       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
  85#  define NUM_RCU_NODES       (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
  86#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
  87#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
  88#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
  89#elif NR_CPUS <= RCU_FANOUT_4
  90#  define RCU_NUM_LVLS        4
  91#  define NUM_RCU_LVL_0       1
  92#  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
  93#  define NUM_RCU_LVL_2       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
  94#  define NUM_RCU_LVL_3       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
  95#  define NUM_RCU_NODES       (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
  96#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
  97#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
  98#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
  99#else
 100# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
 101#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
 102
 103#endif /* __LINUX_RCU_NODE_TREE_H */
 104