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 | |