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