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
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