1 #ifndef _URCU_QSBR_STATIC_H
2 #define _URCU_QSBR_STATIC_H
7 * Userspace RCU QSBR header.
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
10 * dynamically with the userspace rcu QSBR library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
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.
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.
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
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
42 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
44 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
47 * Load a data from shared memory, doing a cache flush if required.
49 #define LOAD_SHARED(p) \
56 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
58 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
61 * Store v into x, where x is located in shared memory. Performs the required
62 * cache flush after writing. Returns v.
64 #define STORE_SHARED(x, v) \
66 _STORE_SHARED(x, v); \
72 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
73 * into a RCU read-side critical section. The pointer can later be safely
74 * dereferenced within the critical section.
76 * This ensures that the pointer copy is invariant thorough the whole critical
79 * Inserts memory barriers on architectures that require them (currently only
80 * Alpha) and documents which pointers are protected by RCU.
82 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
85 #define _rcu_dereference(p) ({ \
86 typeof(p) _________p1 = LOAD_SHARED(p); \
87 smp_read_barrier_depends(); \
92 * This code section can only be included in LGPL 2.1 compatible source code.
93 * See below for the function call wrappers which can be used in code meant to
94 * be only linked with the Userspace RCU library. This comes with a small
95 * performance degradation on the read-side due to the added function calls.
96 * This is required to permit relinking with newer versions of the library.
100 * If a reader is really non-cooperative and refuses to commit its
101 * rcu_reader qs_gp count to memory (there is no barrier in the reader
102 * per-se), kick it after a few loops waiting for it.
104 #define KICK_READER_LOOPS 10000
107 * Active attempts to check for reader Q.S. before calling sched_yield().
109 #define RCU_QS_ACTIVE_ATTEMPTS 100
112 #define rcu_assert(args...) assert(args)
114 #define rcu_assert(args...)
123 #define YIELD_READ (1 << 0)
124 #define YIELD_WRITE (1 << 1)
126 /* maximum sleep delay, in us */
129 extern unsigned int yield_active
;
130 extern unsigned int __thread rand_yield
;
132 static inline void debug_yield_read(void)
134 if (yield_active
& YIELD_READ
)
135 if (rand_r(&rand_yield
) & 0x1)
136 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
139 static inline void debug_yield_write(void)
141 if (yield_active
& YIELD_WRITE
)
142 if (rand_r(&rand_yield
) & 0x1)
143 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
146 static inline void debug_yield_init(void)
148 rand_yield
= time(NULL
) ^ pthread_self();
151 static inline void debug_yield_read(void)
155 static inline void debug_yield_write(void)
159 static inline void debug_yield_init(void)
165 static inline void reader_barrier()
170 #define RCU_GP_ONLINE (1UL << 0)
171 #define RCU_GP_ONGOING (1UL << 1)
172 #define RCU_GP_CTR (1UL << 2)
175 * Global quiescent period counter with low-order bits unused.
176 * Using a int rather than a char to eliminate false register dependencies
177 * causing stalls on some architectures.
179 extern unsigned long urcu_gp_ctr
;
181 struct urcu_reader_status
{
183 unsigned long gp_waiting
;
186 extern struct urcu_reader_status __thread urcu_reader_status
;
188 #if (BITS_PER_LONG < 64)
189 static inline int rcu_gp_ongoing(unsigned long *value
)
191 unsigned long reader_gp
;
195 reader_gp
= LOAD_SHARED(*value
);
196 return reader_gp
&& ((reader_gp
^ urcu_gp_ctr
) & RCU_GP_CTR
);
198 #else /* !(BITS_PER_LONG < 64) */
199 static inline int rcu_gp_ongoing(unsigned long *value
)
201 unsigned long reader_gp
;
205 reader_gp
= LOAD_SHARED(*value
);
206 return reader_gp
&& (reader_gp
- urcu_gp_ctr
> ULONG_MAX
/ 2);
208 #endif /* !(BITS_PER_LONG < 64) */
210 static inline void _rcu_read_lock(void)
212 rcu_assert(urcu_reader_status
.qs_gp
);
215 static inline void _rcu_read_unlock(void)
219 static inline void _rcu_quiescent_state(void)
225 * volatile accesses can be reordered by the compiler when put in the
228 if (unlikely((gp_ctr
= LOAD_SHARED(urcu_gp_ctr
)) & RCU_GP_ONGOING
) &&
229 unlikely(urcu_reader_status
.gp_waiting
)) {
230 _STORE_SHARED(urcu_reader_status
.qs_gp
, gp_ctr
);
233 _STORE_SHARED(urcu_reader_status
.qs_gp
, gp_ctr
);
238 static inline void _rcu_thread_offline(void)
241 STORE_SHARED(urcu_reader_status
.qs_gp
, 0);
242 if (unlikely(LOAD_SHARED(urcu_gp_ctr
) & RCU_GP_ONGOING
) &&
243 unlikely(urcu_reader_status
.gp_waiting
)) {
248 static inline void _rcu_thread_online(void)
250 _STORE_SHARED(urcu_reader_status
.qs_gp
, LOAD_SHARED(urcu_gp_ctr
));
255 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
256 * meant to be read by RCU read-side critical sections. Returns the assigned
259 * Documents which pointers will be dereferenced by RCU read-side critical
260 * sections and adds the required memory barriers on architectures requiring
261 * them. It also makes sure the compiler does not reorder code initializing the
262 * data structure before its publication.
264 * Should match rcu_dereference_pointer().
267 #define _rcu_assign_pointer(p, v) \
269 if (!__builtin_constant_p(v) || \
272 STORE_SHARED(p, v); \
276 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
277 * is as expected by "old". If succeeds, returns the previous pointer to the
278 * data structure, which can be safely freed after waiting for a quiescent state
279 * using synchronize_rcu(). If fails (unexpected value), returns old (which
280 * should not be freed !).
283 #define _rcu_cmpxchg_pointer(p, old, _new) \
285 if (!__builtin_constant_p(_new) || \
288 cmpxchg(p, old, _new); \
292 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
293 * pointer to the data structure, which can be safely freed after waiting for a
294 * quiescent state using synchronize_rcu().
297 #define _rcu_xchg_pointer(p, v) \
299 if (!__builtin_constant_p(v) || \
306 * Exchanges the pointer and waits for quiescent state.
307 * The pointer returned can be freed.
309 #define _rcu_publish_content(p, v) \
312 oldptr = _rcu_xchg_pointer(p, v); \
317 #endif /* _URCU_QSBR_STATIC_H */