qsbr: micro optimization of the gp use.
[urcu.git] / urcu-qsbr-static.h
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1#ifndef _URCU_QSBR_STATIC_H
2#define _URCU_QSBR_STATIC_H
3
4/*
5 * urcu-qsbr-static.h
6 *
7 * Userspace RCU QSBR header.
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
10 * dynamically with the userspace rcu QSBR library.
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#include <assert.h>
35
36#include <compiler.h>
37#include <arch.h>
38
39/*
40 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
41 */
42#define _LOAD_SHARED(p) ACCESS_ONCE(p)
43
44/*
45 * Load a data from shared memory, doing a cache flush if required.
46 */
47#define LOAD_SHARED(p) \
48 ({ \
49 smp_rmc(); \
50 _LOAD_SHARED(p); \
51 })
52
53/*
54 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
55 */
56#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
57
58/*
59 * Store v into x, where x is located in shared memory. Performs the required
60 * cache flush after writing. Returns v.
61 */
62#define STORE_SHARED(x, v) \
63 ({ \
64 _STORE_SHARED(x, v); \
65 smp_wmc(); \
66 (v); \
67 })
68
69/**
70 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
71 * into a RCU read-side critical section. The pointer can later be safely
72 * dereferenced within the critical section.
73 *
74 * This ensures that the pointer copy is invariant thorough the whole critical
75 * section.
76 *
77 * Inserts memory barriers on architectures that require them (currently only
78 * Alpha) and documents which pointers are protected by RCU.
79 *
80 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
81 */
82
83#define _rcu_dereference(p) ({ \
84 typeof(p) _________p1 = LOAD_SHARED(p); \
85 smp_read_barrier_depends(); \
86 (_________p1); \
87 })
88
89/*
90 * This code section can only be included in LGPL 2.1 compatible source code.
91 * See below for the function call wrappers which can be used in code meant to
92 * be only linked with the Userspace RCU library. This comes with a small
93 * performance degradation on the read-side due to the added function calls.
94 * This is required to permit relinking with newer versions of the library.
95 */
96
97/*
98 * If a reader is really non-cooperative and refuses to commit its
99 * rcu_reader_qs_gp count to memory (there is no barrier in the reader
100 * per-se), kick it after a few loops waiting for it.
101 */
102#define KICK_READER_LOOPS 10000
103
104#ifdef DEBUG_RCU
105#define rcu_assert(args...) assert(args)
106#else
107#define rcu_assert(args...)
108#endif
109
110#ifdef DEBUG_YIELD
111#include <sched.h>
112#include <time.h>
113#include <pthread.h>
114#include <unistd.h>
115
116#define YIELD_READ (1 << 0)
117#define YIELD_WRITE (1 << 1)
118
119/* maximum sleep delay, in us */
120#define MAX_SLEEP 50
121
122extern unsigned int yield_active;
123extern unsigned int __thread rand_yield;
124
125static inline void debug_yield_read(void)
126{
127 if (yield_active & YIELD_READ)
128 if (rand_r(&rand_yield) & 0x1)
129 usleep(rand_r(&rand_yield) % MAX_SLEEP);
130}
131
132static inline void debug_yield_write(void)
133{
134 if (yield_active & YIELD_WRITE)
135 if (rand_r(&rand_yield) & 0x1)
136 usleep(rand_r(&rand_yield) % MAX_SLEEP);
137}
138
139static inline void debug_yield_init(void)
140{
141 rand_yield = time(NULL) ^ pthread_self();
142}
143#else
144static inline void debug_yield_read(void)
145{
146}
147
148static inline void debug_yield_write(void)
149{
150}
151
152static inline void debug_yield_init(void)
153{
154
155}
156#endif
157
158static inline void reader_barrier()
159{
160 smp_mb();
161}
162
163/*
164 * Global quiescent period counter with low-order bits unused.
165 * Using a int rather than a char to eliminate false register dependencies
166 * causing stalls on some architectures.
167 */
168extern long urcu_gp_ctr;
169
170extern long __thread rcu_reader_qs_gp;
171
172static inline int rcu_gp_ongoing(long *value)
173{
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174 long reader_gp;
175
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176 if (value == NULL)
177 return 0;
4e560c17 178 reader_gp = LOAD_SHARED(*value);
ab179a17 179 return reader_gp && (reader_gp - urcu_gp_ctr < 0);
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180}
181
182static inline void _rcu_read_lock(void)
183{
184 rcu_assert(rcu_reader_qs_gp & 1);
185}
186
187static inline void _rcu_read_unlock(void)
188{
189}
190
191static inline void _rcu_quiescent_state(void)
192{
193 smp_mb();
ab179a17 194 _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
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195 smp_mb();
196}
197
198static inline void _rcu_thread_offline(void)
199{
200 smp_mb();
4e560c17 201 STORE_SHARED(rcu_reader_qs_gp, 0);
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202}
203
204static inline void _rcu_thread_online(void)
205{
ab179a17 206 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
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207 smp_mb();
208}
209
210/**
211 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
212 * meant to be read by RCU read-side critical sections. Returns the assigned
213 * value.
214 *
215 * Documents which pointers will be dereferenced by RCU read-side critical
216 * sections and adds the required memory barriers on architectures requiring
217 * them. It also makes sure the compiler does not reorder code initializing the
218 * data structure before its publication.
219 *
220 * Should match rcu_dereference_pointer().
221 */
222
223#define _rcu_assign_pointer(p, v) \
224 ({ \
225 if (!__builtin_constant_p(v) || \
226 ((v) != NULL)) \
227 wmb(); \
228 STORE_SHARED(p, v); \
229 })
230
231/**
232 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
233 * pointer to the data structure, which can be safely freed after waiting for a
234 * quiescent state using synchronize_rcu().
235 */
236
237#define _rcu_xchg_pointer(p, v) \
238 ({ \
239 if (!__builtin_constant_p(v) || \
240 ((v) != NULL)) \
241 wmb(); \
242 xchg(p, v); \
243 })
244
245/*
246 * Exchanges the pointer and waits for quiescent state.
247 * The pointer returned can be freed.
248 */
249#define _rcu_publish_content(p, v) \
250 ({ \
251 void *oldptr; \
252 oldptr = _rcu_xchg_pointer(p, v); \
253 synchronize_rcu(); \
254 oldptr; \
255 })
256
257#endif /* _URCU_QSBR_STATIC_H */
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