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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/*
24 * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
25 * CONFIG_RCU_FANOUT_LEAF.
26 * In theory, it should be possible to add more levels straightforwardly.
27 * In practice, this did work well going from three levels to four.
28 * Of course, your mileage may vary.
29 */
30
31#ifdef CONFIG_RCU_FANOUT
32#define RCU_FANOUT CONFIG_RCU_FANOUT
33#else /* #ifdef CONFIG_RCU_FANOUT */
34# ifdef CONFIG_64BIT
35# define RCU_FANOUT 64
36# else
37# define RCU_FANOUT 32
38# endif
39#endif /* #else #ifdef CONFIG_RCU_FANOUT */
40
41#ifdef CONFIG_RCU_FANOUT_LEAF
42#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
43#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
44#define RCU_FANOUT_LEAF 16
45#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
46
47#define RCU_FANOUT_1 (RCU_FANOUT_LEAF)
48#define RCU_FANOUT_2 (RCU_FANOUT_1 * RCU_FANOUT)
49#define RCU_FANOUT_3 (RCU_FANOUT_2 * RCU_FANOUT)
50#define RCU_FANOUT_4 (RCU_FANOUT_3 * RCU_FANOUT)
51
52#if NR_CPUS <= RCU_FANOUT_1
53# define RCU_NUM_LVLS 1
54# define NUM_RCU_LVL_0 1
55# define NUM_RCU_NODES NUM_RCU_LVL_0
56# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0 }
57# define RCU_NODE_NAME_INIT { "rcu_node_0" }
58# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0" }
59#elif NR_CPUS <= RCU_FANOUT_2
60# define RCU_NUM_LVLS 2
61# define NUM_RCU_LVL_0 1
62# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
63# define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
64# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
65# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1" }
66# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1" }
67#elif NR_CPUS <= RCU_FANOUT_3
68# define RCU_NUM_LVLS 3
69# define NUM_RCU_LVL_0 1
70# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
71# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
72# define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
73# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
74# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
75# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
76#elif NR_CPUS <= RCU_FANOUT_4
77# define RCU_NUM_LVLS 4
78# define NUM_RCU_LVL_0 1
79# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
80# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
81# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
82# define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
83# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
84# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
85# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
86#else
87# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
88#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
89
90#endif /* __LINUX_RCU_NODE_TREE_H */