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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 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.
14 *
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.
19 *
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.
23 *
24 * Copyright IBM Corporation, 2017
25 *
26 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 */
28
29#ifndef __LINUX_RCU_NODE_TREE_H
30#define __LINUX_RCU_NODE_TREE_H
31
32/*
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.
38 */
39
40#ifdef CONFIG_RCU_FANOUT
41#define RCU_FANOUT CONFIG_RCU_FANOUT
42#else /* #ifdef CONFIG_RCU_FANOUT */
43# ifdef CONFIG_64BIT
44# define RCU_FANOUT 64
45# else
46# define RCU_FANOUT 32
47# endif
48#endif /* #else #ifdef CONFIG_RCU_FANOUT */
49
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 */
55
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)
60
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" }
95#else
96# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
97#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
98
99#endif /* __LINUX_RCU_NODE_TREE_H */