include/linux/rcu_node_tree.h

   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 */