include/linux/rcu_node_tree.h

   1 /* SPDX-License-Identifier: GPL-2.0+ */
   2 /*
   3  * RCU node combining tree definitions.  These are used to compute
   4  * global attributes while avoiding common-case global contention.  A key
   5  * property that these computations rely on is a tournament-style approach
   6  * where only one of the tasks contending a lower level in the tree need
   7  * advance to the next higher level.  If properly configured, this allows
   8  * unlimited scalability while maintaining a constant level of contention
   9  * on the root node.
  10  *
  11  * This seemingly RCU-private file must be available to SRCU users
  12  * because the size of the TREE SRCU srcu_struct structure depends
  13  * on these definitions.
  14  *
  15  * Copyright IBM Corporation, 2017
  16  *
  17  * Author: Paul E. McKenney <paulmck@linux.ibm.com>
  18  */
  19
  20 #ifndef __LINUX_RCU_NODE_TREE_H
  21 #define __LINUX_RCU_NODE_TREE_H
  22
  23 #include <linux/math.h>
  24
  25 /*
  26  * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
  27  * CONFIG_RCU_FANOUT_LEAF.
  28  * In theory, it should be possible to add more levels straightforwardly.
  29  * In practice, this did work well going from three levels to four.
  30  * Of course, your mileage may vary.
  31  */
  32
  33 #ifdef CONFIG_RCU_FANOUT
  34 #define RCU_FANOUT CONFIG_RCU_FANOUT
  35 #else /* #ifdef CONFIG_RCU_FANOUT */
  36 # ifdef CONFIG_64BIT
  37 # define RCU_FANOUT 64
  38 # else
  39 # define RCU_FANOUT 32
  40 # endif
  41 #endif /* #else #ifdef CONFIG_RCU_FANOUT */
  42
  43 #ifdef CONFIG_RCU_FANOUT_LEAF
  44 #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
  45 #else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
  46 #define RCU_FANOUT_LEAF 16
  47 #endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
  48
  49 #define RCU_FANOUT_1          (RCU_FANOUT_LEAF)
  50 #define RCU_FANOUT_2          (RCU_FANOUT_1 * RCU_FANOUT)
  51 #define RCU_FANOUT_3          (RCU_FANOUT_2 * RCU_FANOUT)
  52 #define RCU_FANOUT_4          (RCU_FANOUT_3 * RCU_FANOUT)
  53
  54 #if NR_CPUS <= RCU_FANOUT_1
  55 #  define RCU_NUM_LVLS        1
  56 #  define NUM_RCU_LVL_0       1
  57 #  define NUM_RCU_NODES       NUM_RCU_LVL_0
  58 #  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0 }
  59 #  define RCU_NODE_NAME_INIT  { "rcu_node_0" }
  60 #  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0" }
  61 #elif NR_CPUS <= RCU_FANOUT_2
  62 #  define RCU_NUM_LVLS        2
  63 #  define NUM_RCU_LVL_0       1
  64 #  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
  65 #  define NUM_RCU_NODES       (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
  66 #  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
  67 #  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1" }
  68 #  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1" }
  69 #elif NR_CPUS <= RCU_FANOUT_3
  70 #  define RCU_NUM_LVLS        3
  71 #  define NUM_RCU_LVL_0       1
  72 #  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
  73 #  define NUM_RCU_LVL_2       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
  74 #  define NUM_RCU_NODES       (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
  75 #  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
  76 #  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
  77 #  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
  78 #elif NR_CPUS <= RCU_FANOUT_4
  79 #  define RCU_NUM_LVLS        4
  80 #  define NUM_RCU_LVL_0       1
  81 #  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
  82 #  define NUM_RCU_LVL_2       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
  83 #  define NUM_RCU_LVL_3       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
  84 #  define NUM_RCU_NODES       (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
  85 #  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
  86 #  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
  87 #  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
  88 #else
  89 # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
  90 #endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
  91
  92 #endif /* __LINUX_RCU_NODE_TREE_H */