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.
43 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
45 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
48 * Load a data from shared memory, doing a cache flush if required.
50 #define LOAD_SHARED(p) \
57 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
59 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
62 * Store v into x, where x is located in shared memory. Performs the required
63 * cache flush after writing. Returns v.
65 #define STORE_SHARED(x, v) \
67 _STORE_SHARED(x, v); \
73 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
74 * into a RCU read-side critical section. The pointer can later be safely
75 * dereferenced within the critical section.
77 * This ensures that the pointer copy is invariant thorough the whole critical
80 * Inserts memory barriers on architectures that require them (currently only
81 * Alpha) and documents which pointers are protected by RCU.
83 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
86 #define _rcu_dereference(p) ({ \
87 typeof(p) _________p1 = LOAD_SHARED(p); \
88 smp_read_barrier_depends(); \
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.
101 * If a reader is really non-cooperative and refuses to commit its
102 * rcu_reader qs_gp count to memory (there is no barrier in the reader
103 * per-se), kick it after a few loops waiting for it.
105 #define KICK_READER_LOOPS 10000
108 * Active attempts to check for reader Q.S. before calling sched_yield().
110 #define RCU_QS_ACTIVE_ATTEMPTS 100
113 #define rcu_assert(args...) assert(args)
115 #define rcu_assert(args...)
124 #define YIELD_READ (1 << 0)
125 #define YIELD_WRITE (1 << 1)
127 /* maximum sleep delay, in us */
130 extern unsigned int yield_active
;
131 extern unsigned int __thread rand_yield
;
133 static inline void debug_yield_read(void)
135 if (yield_active
& YIELD_READ
)
136 if (rand_r(&rand_yield
) & 0x1)
137 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
140 static inline void debug_yield_write(void)
142 if (yield_active
& YIELD_WRITE
)
143 if (rand_r(&rand_yield
) & 0x1)
144 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
147 static inline void debug_yield_init(void)
149 rand_yield
= time(NULL
) ^ pthread_self();
152 static inline void debug_yield_read(void)
156 static inline void debug_yield_write(void)
160 static inline void debug_yield_init(void)
166 static inline void reader_barrier()
171 #define RCU_GP_ONLINE (1UL << 0)
172 #define RCU_GP_ONGOING (1UL << 1)
173 #define RCU_GP_CTR (1UL << 2)
176 * Global quiescent period counter with low-order bits unused.
177 * Using a int rather than a char to eliminate false register dependencies
178 * causing stalls on some architectures.
180 extern unsigned long urcu_gp_ctr
;
182 struct urcu_reader_status
{
184 unsigned long gp_waiting
;
185 unsigned long qs_time_delta_usec
;
186 struct timeval qs_time_last
;
189 extern struct urcu_reader_status __thread urcu_reader_status
;
191 #if (BITS_PER_LONG < 64)
192 static inline int rcu_gp_ongoing(unsigned long *value
)
194 unsigned long reader_gp
;
198 reader_gp
= LOAD_SHARED(*value
);
199 return reader_gp
&& ((reader_gp
^ urcu_gp_ctr
) & RCU_GP_CTR
);
201 #else /* !(BITS_PER_LONG < 64) */
202 static inline int rcu_gp_ongoing(unsigned long *value
)
204 unsigned long reader_gp
;
208 reader_gp
= LOAD_SHARED(*value
);
209 return reader_gp
&& (reader_gp
- urcu_gp_ctr
> ULONG_MAX
/ 2);
211 #endif /* !(BITS_PER_LONG < 64) */
213 static inline void _rcu_read_lock(void)
215 rcu_assert(urcu_reader_status
.qs_gp
);
218 static inline void _rcu_read_unlock(void)
222 static inline void _rcu_quiescent_state(void)
225 struct timeval current_time
, delta_time
;
228 gettimeofday(¤t_time
, NULL
);
229 timersub(¤t_time
, &urcu_reader_status
.qs_time_last
, &delta_time
);
230 if (delta_time
.tv_sec
>= 1)
231 _STORE_SHARED(urcu_reader_status
.qs_time_delta_usec
, 1000000);
233 _STORE_SHARED(urcu_reader_status
.qs_time_delta_usec
,
234 (unsigned long)delta_time
.tv_usec
);
235 urcu_reader_status
.qs_time_last
= current_time
;
237 * volatile accesses can be reordered by the compiler when put in the
240 if (unlikely((gp_ctr
= LOAD_SHARED(urcu_gp_ctr
)) & RCU_GP_ONGOING
) &&
241 unlikely(urcu_reader_status
.gp_waiting
)) {
242 _STORE_SHARED(urcu_reader_status
.qs_gp
, gp_ctr
);
245 _STORE_SHARED(urcu_reader_status
.qs_gp
, gp_ctr
);
250 static inline void _rcu_thread_offline(void)
253 STORE_SHARED(urcu_reader_status
.qs_gp
, 0);
254 if (unlikely(LOAD_SHARED(urcu_gp_ctr
) & RCU_GP_ONGOING
) &&
255 unlikely(urcu_reader_status
.gp_waiting
)) {
260 static inline void _rcu_thread_online(void)
262 struct timeval current_time
, delta_time
;
264 gettimeofday(¤t_time
, NULL
);
265 timersub(¤t_time
, &urcu_reader_status
.qs_time_last
, &delta_time
);
266 if (delta_time
.tv_sec
>= 1)
267 _STORE_SHARED(urcu_reader_status
.qs_time_delta_usec
, 1000000);
269 _STORE_SHARED(urcu_reader_status
.qs_time_delta_usec
,
270 (unsigned long)delta_time
.tv_usec
);
271 urcu_reader_status
.qs_time_last
= current_time
;
272 _STORE_SHARED(urcu_reader_status
.qs_time_delta_usec
, 0);
273 _STORE_SHARED(urcu_reader_status
.qs_gp
, LOAD_SHARED(urcu_gp_ctr
));
278 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
279 * meant to be read by RCU read-side critical sections. Returns the assigned
282 * Documents which pointers will be dereferenced by RCU read-side critical
283 * sections and adds the required memory barriers on architectures requiring
284 * them. It also makes sure the compiler does not reorder code initializing the
285 * data structure before its publication.
287 * Should match rcu_dereference_pointer().
290 #define _rcu_assign_pointer(p, v) \
292 if (!__builtin_constant_p(v) || \
295 STORE_SHARED(p, v); \
299 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
300 * is as expected by "old". If succeeds, returns the previous pointer to the
301 * data structure, which can be safely freed after waiting for a quiescent state
302 * using synchronize_rcu(). If fails (unexpected value), returns old (which
303 * should not be freed !).
306 #define _rcu_cmpxchg_pointer(p, old, _new) \
308 if (!__builtin_constant_p(_new) || \
311 cmpxchg(p, old, _new); \
315 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
316 * pointer to the data structure, which can be safely freed after waiting for a
317 * quiescent state using synchronize_rcu().
320 #define _rcu_xchg_pointer(p, v) \
322 if (!__builtin_constant_p(v) || \
329 * Exchanges the pointer and waits for quiescent state.
330 * The pointer returned can be freed.
332 #define _rcu_publish_content(p, v) \
335 oldptr = _rcu_xchg_pointer(p, v); \
340 #endif /* _URCU_QSBR_STATIC_H */