| /* SPDX-License-Identifier: GPL-2.0+ */ |
| /* |
| * RCU node combining tree definitions. These are used to compute |
| * global attributes while avoiding common-case global contention. A key |
| * property that these computations rely on is a tournament-style approach |
| * where only one of the tasks contending a lower level in the tree need |
| * advance to the next higher level. If properly configured, this allows |
| * unlimited scalability while maintaining a constant level of contention |
| * on the root node. |
| * |
| * This seemingly RCU-private file must be available to SRCU users |
| * because the size of the TREE SRCU srcu_struct structure depends |
| * on these definitions. |
| * |
| * Copyright IBM Corporation, 2017 |
| * |
| * Author: Paul E. McKenney <paulmck@linux.ibm.com> |
| */ |
| |
| #ifndef __LINUX_RCU_NODE_TREE_H |
| #define __LINUX_RCU_NODE_TREE_H |
| |
| #include <linux/math.h> |
| |
| /* |
| * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and |
| * CONFIG_RCU_FANOUT_LEAF. |
| * In theory, it should be possible to add more levels straightforwardly. |
| * In practice, this did work well going from three levels to four. |
| * Of course, your mileage may vary. |
| */ |
| |
| #ifdef CONFIG_RCU_FANOUT |
| #define RCU_FANOUT CONFIG_RCU_FANOUT |
| #else /* #ifdef CONFIG_RCU_FANOUT */ |
| # ifdef CONFIG_64BIT |
| # define RCU_FANOUT 64 |
| # else |
| # define RCU_FANOUT 32 |
| # endif |
| #endif /* #else #ifdef CONFIG_RCU_FANOUT */ |
| |
| #ifdef CONFIG_RCU_FANOUT_LEAF |
| #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF |
| #else /* #ifdef CONFIG_RCU_FANOUT_LEAF */ |
| #define RCU_FANOUT_LEAF 16 |
| #endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */ |
| |
| #define RCU_FANOUT_1 (RCU_FANOUT_LEAF) |
| #define RCU_FANOUT_2 (RCU_FANOUT_1 * RCU_FANOUT) |
| #define RCU_FANOUT_3 (RCU_FANOUT_2 * RCU_FANOUT) |
| #define RCU_FANOUT_4 (RCU_FANOUT_3 * RCU_FANOUT) |
| |
| #if NR_CPUS <= RCU_FANOUT_1 |
| # define RCU_NUM_LVLS 1 |
| # define NUM_RCU_LVL_0 1 |
| # define NUM_RCU_NODES NUM_RCU_LVL_0 |
| # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0 } |
| # define RCU_NODE_NAME_INIT { "rcu_node_0" } |
| # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0" } |
| #elif NR_CPUS <= RCU_FANOUT_2 |
| # define RCU_NUM_LVLS 2 |
| # define NUM_RCU_LVL_0 1 |
| # define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) |
| # define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1) |
| # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1 } |
| # define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1" } |
| # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1" } |
| #elif NR_CPUS <= RCU_FANOUT_3 |
| # define RCU_NUM_LVLS 3 |
| # define NUM_RCU_LVL_0 1 |
| # define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2) |
| # define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) |
| # define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2) |
| # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 } |
| # define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2" } |
| # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" } |
| #elif NR_CPUS <= RCU_FANOUT_4 |
| # define RCU_NUM_LVLS 4 |
| # define NUM_RCU_LVL_0 1 |
| # define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3) |
| # define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2) |
| # define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) |
| # define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3) |
| # define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 } |
| # define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" } |
| # define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" } |
| #else |
| # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS" |
| #endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */ |
| |
| #endif /* __LINUX_RCU_NODE_TREE_H */ |
