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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 */