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 */ 93