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[urcu.git] / urcu-defer-static.h
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1#ifndef _URCU_DEFER_STATIC_H
2#define _URCU_DEFER_STATIC_H
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3
4/*
786ee85b 5 * urcu-defer-static.h
90075a50 6 *
658225a7 7 * Userspace RCU header - memory reclamation.
90075a50 8 *
786ee85b 9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-defer.h for linking
658225a7 10 * dynamically with the userspace rcu reclamation library.
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11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
14 *
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
19 *
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
24 *
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
28 *
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
30 */
31
32#include <stdlib.h>
33#include <pthread.h>
34
35#include <compiler.h>
36#include <arch.h>
37
38
39/*
786ee85b 40 * Number of entries in the per-thread defer queue. Must be power of 2.
90075a50 41 */
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42#define DEFER_QUEUE_SIZE (1 << 12)
43#define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
90075a50 44
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45/*
46 * Typically, data is aligned at least on the architecture size.
47 * Use lowest bit to indicate that the current callback is changing.
48 * Assumes that (void *)-2L is not used often. Used to encode non-aligned
49 * functions and non-aligned data using extra space.
50 * We encode the (void *)-2L fct as: -2L, fct, data.
51 * We encode the (void *)-2L data as: -2L, fct, data.
52 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
53 */
54#define DQ_FCT_BIT (1 << 0)
55#define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
56#define DQ_SET_FCT_BIT(x) \
57 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
58#define DQ_CLEAR_FCT_BIT(x) \
59 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
60#define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
61
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62/*
63 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
64 */
65#define _LOAD_SHARED(p) ACCESS_ONCE(p)
66
67/*
68 * Load a data from shared memory, doing a cache flush if required.
69 */
70#define LOAD_SHARED(p) \
71 ({ \
72 smp_rmc(); \
73 _LOAD_SHARED(p); \
74 })
75
76/*
77 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
78 */
79#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
80
81/*
82 * Store v into x, where x is located in shared memory. Performs the required
83 * cache flush after writing. Returns v.
84 */
85#define STORE_SHARED(x, v) \
86 ({ \
87 _STORE_SHARED(x, v); \
88 smp_wmc(); \
89 (v); \
90 })
91
92/*
93 * This code section can only be included in LGPL 2.1 compatible source code.
94 * See below for the function call wrappers which can be used in code meant to
95 * be only linked with the Userspace RCU library. This comes with a small
96 * performance degradation on the read-side due to the added function calls.
97 * This is required to permit relinking with newer versions of the library.
98 */
99
100#ifdef DEBUG_RCU
101#define rcu_assert(args...) assert(args)
102#else
103#define rcu_assert(args...)
104#endif
105
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106/*
107 * defer queue.
108 * Contains pointers. Encoded to save space when same callback is often used.
109 * When looking up the next item:
110 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
111 * - next element contains pointer to data.
112 * - else if item == DQ_FCT_MARK
113 * - set the current callback to next element ptr
114 * - following next element contains pointer to data.
115 * - else current element contains data
116 */
786ee85b 117struct defer_queue {
90075a50 118 unsigned long head; /* add element at head */
804b4375 119 void *last_fct_in; /* last fct pointer encoded */
90075a50 120 unsigned long tail; /* next element to remove at tail */
804b4375 121 void *last_fct_out; /* last fct pointer encoded */
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122 void **q;
123};
124
786ee85b 125extern struct defer_queue __thread defer_queue;
90075a50 126
786ee85b 127extern void rcu_defer_barrier_thread(void);
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128
129/*
130 * not signal-safe.
131 */
804b4375 132static inline void _rcu_defer_queue(void (*fct)(void *p), void *p)
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133{
134 unsigned long head, tail;
135
136 /*
137 * Head is only modified by ourself. Tail can be modified by reclamation
138 * thread.
139 */
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140 head = defer_queue.head;
141 tail = LOAD_SHARED(defer_queue.tail);
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142
143 /*
144 * If queue is full, empty it ourself.
804b4375 145 * Worse-case: must allow 2 supplementary entries for fct pointer.
90075a50 146 */
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147 if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
148 assert(head - tail <= DEFER_QUEUE_SIZE);
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149 rcu_defer_barrier_thread();
150 assert(head - LOAD_SHARED(defer_queue.tail) == 0);
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151 }
152
804b4375 153 if (unlikely(defer_queue.last_fct_in != fct)) {
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154 defer_queue.last_fct_in = fct;
155 if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
156 /*
157 * If the function to encode is not aligned or the
158 * marker, write DQ_FCT_MARK followed by the function
159 * pointer.
160 */
161 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
162 DQ_FCT_MARK);
163 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
164 fct);
165 } else {
166 DQ_SET_FCT_BIT(fct);
167 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
168 fct);
169 }
170 } else {
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171 if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
172 /*
173 * If the data to encode is not aligned or the marker,
174 * write DQ_FCT_MARK followed by the function pointer.
175 */
176 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
177 DQ_FCT_MARK);
178 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
179 fct);
180 }
181 }
182 _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
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183 smp_wmb(); /* Publish new pointer before head */
184 /* Write q[] before head. */
804b4375 185 STORE_SHARED(defer_queue.head, head);
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186}
187
786ee85b 188#endif /* _URCU_DEFER_STATIC_H */
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