Use statistical approach to approximate the max number of nodes per population
[userspace-rcu.git] / rcuja / rcuja.c
1 /*
2 * rcuja/rcuja.c
3 *
4 * Userspace RCU library - RCU Judy Array
5 *
6 * Copyright 2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 *
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 */
22
23 #include <stdint.h>
24 #include <limits.h>
25 #include <urcu/rcuja.h>
26 #include <urcu/compiler.h>
27 #include <urcu/arch.h>
28 #include <assert.h>
29 #include "rcuja-internal.h"
30 #include "bitfield.h"
31
32 enum rcu_ja_type_class {
33 RCU_JA_LINEAR = 0, /* Type A */
34 /* 32-bit: 1 to 25 children, 8 to 128 bytes */
35 /* 64-bit: 1 to 28 children, 16 to 256 bytes */
36 RCU_JA_POOL = 1, /* Type B */
37 /* 32-bit: 26 to 100 children, 256 to 512 bytes */
38 /* 64-bit: 29 to 112 children, 512 to 1024 bytes */
39 RCU_JA_PIGEON = 2, /* Type C */
40 /* 32-bit: 101 to 256 children, 1024 bytes */
41 /* 64-bit: 113 to 256 children, 2048 bytes */
42 /* Leaf nodes are implicit from their height in the tree */
43 };
44
45 struct rcu_ja_type {
46 enum rcu_ja_type_class type_class;
47 uint16_t min_child; /* minimum number of children: 1 to 256 */
48 uint16_t max_child; /* maximum number of children: 1 to 256 */
49 uint16_t order; /* node size is (1 << order), in bytes */
50 uint16_t nr_pool_order; /* number of pools */
51 uint16_t pool_size_order; /* pool size */
52 };
53
54 /*
55 * Number of least significant pointer bits reserved to represent the
56 * child type.
57 */
58 #define JA_TYPE_BITS 3
59 #define JA_TYPE_MAX_NR (1U << JA_TYPE_BITS)
60 #define JA_TYPE_MASK (JA_TYPE_MAX_NR - 1)
61 #define JA_PTR_MASK (~JA_TYPE_MASK)
62
63 #define JA_ENTRY_PER_NODE 256UL
64
65 /*
66 * Iteration on the array to find the right node size for the number of
67 * children stops when it reaches .max_child == 256 (this is the largest
68 * possible node size, which contains 256 children).
69 * The min_child overlaps with the previous max_child to provide an
70 * hysteresis loop to reallocation for patterns of cyclic add/removal
71 * within the same node.
72 * The node the index within the following arrays is represented on 3
73 * bits. It identifies the node type, min/max number of children, and
74 * the size order.
75 * The max_child values for the RCU_JA_POOL below result from
76 * statistical approximation: over million populations, the max_child
77 * covers between 97% and 99% of the populations generated. Therefore, a
78 * fallback should exist to cover the rare extreme population unbalance
79 * cases, but it will not have a major impact on speed nor space
80 * consumption, since those are rare cases.
81 */
82
83 #if (CAA_BITS_PER_LONG < 64)
84 /* 32-bit pointers */
85 const struct rcu_ja_type ja_types[] = {
86 { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = 1, .order = 3, },
87 { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = 3, .order = 4, },
88 { .type_class = RCU_JA_LINEAR, .min_child = 3, .max_child = 6, .order = 5, },
89 { .type_class = RCU_JA_LINEAR, .min_child = 4, .max_child = 12, .order = 6, },
90 { .type_class = RCU_JA_LINEAR, .min_child = 10, .max_child = 25, .order = 7, },
91
92 /* Pools may fill sooner than max_child */
93 { .type_class = RCU_JA_POOL, .min_child = 20, .max_child = 48, .order = 8, .nr_pool_order = 1, .pool_size_order = 7, },
94 { .type_class = RCU_JA_POOL, .min_child = 45, .max_child = 92, .order = 9, .nr_pool_order = 2, .pool_size_order = 7, },
95
96 /*
97 * TODO: Upon node removal below min_child, if child pool is
98 * filled beyond capacity, we need to roll back to pigeon.
99 */
100 { .type_class = RCU_JA_PIGEON, .min_child = 89, .max_child = 256, .order = 10, },
101 };
102 CAA_BUILD_BUG_ON(CAA_ARRAY_SIZE(ja_types) > JA_TYPE_MAX_NR);
103 #else /* !(CAA_BITS_PER_LONG < 64) */
104 /* 64-bit pointers */
105 const struct rcu_ja_type ja_types[] = {
106 { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = 1, .order = 4, },
107 { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = 3, .order = 5, },
108 { .type_class = RCU_JA_LINEAR, .min_child = 3, .max_child = 7, .order = 6, },
109 { .type_class = RCU_JA_LINEAR, .min_child = 5, .max_child = 14, .order = 7, },
110 { .type_class = RCU_JA_LINEAR, .min_child = 10, .max_child = 28, .order = 8, },
111
112 /* Pools may fill sooner than max_child. */
113 { .type_class = RCU_JA_POOL, .min_child = 22, .max_child = 54, .order = 9, .nr_pool_order = 1, .pool_size_order = 8, },
114 { .type_class = RCU_JA_POOL, .min_child = 51, .max_child = 104, .order = 10, .nr_pool_order = 2, .pool_size_order = 8, },
115
116 /*
117 * TODO: Upon node removal below min_child, if child pool is
118 * filled beyond capacity, we need to roll back to pigeon.
119 */
120 { .type_class = RCU_JA_PIGEON, .min_child = 101, .max_child = 256, .order = 11, },
121 };
122 CAA_BUILD_BUG_ON(CAA_ARRAY_SIZE(ja_types) > JA_TYPE_MAX_NR);
123 #endif /* !(BITS_PER_LONG < 64) */
124
125 /*
126 * The rcu_ja_node starts with a byte counting the number of children in
127 * the node. Then, the node-specific data is placed.
128 * TODO: where should we put the mutex for the node ?
129 * -> mutex could be a 0-value node count.
130 * TODO: where do we keep nr children for pigeon ?
131 */
132 struct rcu_ja_node {
133 char data[];
134 };
135
136 /* Never declared. Opaque type used to store flagged node pointers. */
137 struct rcu_ja_node_flag;
138
139 static
140 struct rcu_ja_node_flag *ja_node_flag(struct rcu_ja_node *node, unsigned int type)
141 {
142 assert(type < JA_TYPE_NR);
143 return (struct rcu_ja_node_flag *) (((unsigned long) node) | type);
144 }
145
146 static
147 unsigned int ja_node_type(struct rcu_ja_node_flag *node)
148 {
149 unsigned int type;
150
151 type = (unsigned int) ((unsigned long) node & JA_TYPE_MASK);
152 assert(type < JA_TYPE_NR);
153 return type;
154 }
155
156 static
157 struct rcu_ja_node *ja_node_ptr(struct rcu_ja_node_flag *node)
158 {
159 return (struct rcu_ja_node *) (((unsigned long) node) | JA_PTR_MASK);
160 }
161
162 struct rcu_ja_node *alloc_rcu_ja_node(struct rcu_ja_type *ja_type)
163 {
164 return zmalloc(1 << ja_type->node_order);
165 }
166
167 void free_rcu_ja_node(struct rcu_ja_node *node)
168 {
169 free(node);
170 }
171
172 #define __JA_ALIGN_MASK(v, mask) (((v) + (mask)) & ~(mask))
173 #define JA_ALIGN(v, align) __JA_ALIGN_MASK(v, (typeof(v)) (align) - 1)
174 #define __JA_FLOOR_MASK(v, mask) ((v) & ~(mask))
175 #define JA_FLOOR(v, align) __JA_FLOOR_MASK(v, (typeof(v)) (align) - 1)
176
177 static
178 char *align_ptr_size(char *ptr)
179 {
180 return JA_ALIGN(ptr, sizeof(ptr));
181 }
182
183 static
184 struct rcu_ja_node_flag *ja_linear_node_get_nth(const struct rcu_ja_type *type,
185 struct rcu_ja_node *node,
186 uint8_t n)
187 {
188 uint8_t nr_child;
189 uint8_t *values;
190 struct rcu_ja_node_flag *pointers;
191 struct rcu_ja_node_flag *ptr;
192 unsigned int i;
193
194 assert(!type || type->type_class == RCU_JA_LINEAR);
195
196 nr_child = node->data[0];
197 cmm_smp_rmb(); /* read nr_child before values */
198 assert(!type || nr_child <= type->max_child);
199 assert(!type || nr_child >= type->min_child);
200
201 values = &node[1];
202 for (i = 0; i < nr_child; i++) {
203 if (values[i] == n)
204 break;
205 }
206 if (i >= nr_child)
207 return NULL;
208 cmm_smp_rmb(); /* read values before pointer */
209 pointers = align_ptr_size(&values[nr_child]);
210 ptr = pointers[i];
211 assert(ja_node_ptr(ptr) != NULL);
212 return ptr;
213 }
214
215 static
216 struct rcu_ja_node_flag *ja_pool_node_get_nth(const struct rcu_ja_type *type,
217 struct rcu_ja_node *node,
218 uint8_t n)
219 {
220 struct rcu_ja_node_flag *ptr;
221 struct rcu_ja_node *linear;
222
223 assert(type->type_class == RCU_JA_POOL);
224 linear = (struct rcu_ja_node *)
225 &node->data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
226 return ja_linear_node_get_nth(NULL, linear, n);
227 }
228
229 static
230 struct rcu_ja_node_flag *ja_pigeon_node_get_nth(const struct rcu_ja_type *type,
231 struct rcu_ja_node *node,
232 uint8_t n)
233 {
234 assert(type->type_class == RCU_JA_PIGEON);
235 return ((struct rcu_ja_node_flag *) node->data)[n];
236 }
237
238 /* ja_node_get_nth: get nth item from a node */
239 static
240 struct rcu_ja_node_flag *ja_node_get_nth(struct rcu_ja_node_flag *node_flag,
241 uint8_t n)
242 {
243 unsigned int type_index;
244 struct rcu_ja_node *node;
245 const struct rcu_ja_type *type;
246
247 node_flag = rcu_dereference(node_flag);
248 node = ja_node_ptr(node_flag);
249 assert(node != NULL);
250 type_index = ja_node_type(node_flag);
251 type = &ja_types[type_index];
252
253 switch (type->type_class) {
254 case RCU_JA_LINEAR:
255 return ja_linear_node_get_nth(type, node, n);
256 case RCU_JA_POOL:
257 return ja_pool_node_get_nth(type, node, n);
258 case RCU_JA_PIGEON:
259 return ja_pigeon_node_get_nth(type, node, n);
260 default:
261 assert(0);
262 return (void *) -1UL;
263 }
264 }
265
266 /*
267 * ja_node_set_nth: set nth item within a node. asserts that it is not
268 * there yet.
269 */
270
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