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
10 * This program is free software; you can redistribute it and/or modify
11 * it under the terms of the GNU General Public License as published by
12 * the Free Software Foundation; either version 2 of the License, or
13 * (at your option) any later version.
15 * This program is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 * GNU General Public License for more details.
20 * You should have received a copy of the GNU General Public License
21 * along with this program; if not, you can access it online at
22 * http://www.gnu.org/licenses/gpl-2.0.html.
24 * Copyright IBM Corporation, 2017
26 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
29 #ifndef __LINUX_RCU_NODE_TREE_H
30 #define __LINUX_RCU_NODE_TREE_H
33 * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
34 * CONFIG_RCU_FANOUT_LEAF.
35 * In theory, it should be possible to add more levels straightforwardly.
36 * In practice, this did work well going from three levels to four.
37 * Of course, your mileage may vary.
40 #ifdef CONFIG_RCU_FANOUT
41 #define RCU_FANOUT CONFIG_RCU_FANOUT
42 #else /* #ifdef CONFIG_RCU_FANOUT */
44 # define RCU_FANOUT 64
46 # define RCU_FANOUT 32
48 #endif /* #else #ifdef CONFIG_RCU_FANOUT */
50 #ifdef CONFIG_RCU_FANOUT_LEAF
51 #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
52 #else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
53 #define RCU_FANOUT_LEAF 16
54 #endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
56 #define RCU_FANOUT_1 (RCU_FANOUT_LEAF)
57 #define RCU_FANOUT_2 (RCU_FANOUT_1 * RCU_FANOUT)
58 #define RCU_FANOUT_3 (RCU_FANOUT_2 * RCU_FANOUT)
59 #define RCU_FANOUT_4 (RCU_FANOUT_3 * RCU_FANOUT)
61 #if NR_CPUS <= RCU_FANOUT_1
62 # define RCU_NUM_LVLS 1
63 # define NUM_RCU_LVL_0 1
64 # define NUM_RCU_NODES NUM_RCU_LVL_0
65 # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0 }
66 # define RCU_NODE_NAME_INIT { "rcu_node_0" }
67 # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0" }
68 #elif NR_CPUS <= RCU_FANOUT_2
69 # define RCU_NUM_LVLS 2
70 # define NUM_RCU_LVL_0 1
71 # define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
72 # define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
73 # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
74 # define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1" }
75 # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1" }
76 #elif NR_CPUS <= RCU_FANOUT_3
77 # define RCU_NUM_LVLS 3
78 # define NUM_RCU_LVL_0 1
79 # define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
80 # define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
81 # define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
82 # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
83 # define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
84 # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
85 #elif NR_CPUS <= RCU_FANOUT_4
86 # define RCU_NUM_LVLS 4
87 # define NUM_RCU_LVL_0 1
88 # define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
89 # define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
90 # define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
91 # define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
92 # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
93 # define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
94 # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
96 # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
97 #endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
99 #endif /* __LINUX_RCU_NODE_TREE_H */