urcu-qsbr.h

   1 #ifndef _URCU_QSBR_H
   2 #define _URCU_QSBR_H
   3
   4 /*
   5  * urcu-static.h
   6  *
   7  * Userspace RCU header.
   8  *
   9  * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
  10  * dynamically with the userspace rcu 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
  35 #include <compiler.h>
  36 #include <arch.h>
  37
  38 /*
  39  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  40  */
  41 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  42
  43 /*
  44  * Load a data from shared memory, doing a cache flush if required.
  45  */
  46 #define LOAD_SHARED(p)                  \
  47         ({                              \
  48                 smp_rmc();              \
  49                 _LOAD_SHARED(p);        \
  50         })
  51
  52 /*
  53  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  54  */
  55 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  56
  57 /*
  58  * Store v into x, where x is located in shared memory. Performs the required
  59  * cache flush after writing. Returns v.
  60  */
  61 #define STORE_SHARED(x, v)              \
  62         ({                              \
  63                 _STORE_SHARED(x, v);    \
  64                 smp_wmc();              \
  65                 (v);                    \
  66         })
  67
  68 /**
  69  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  70  * into a RCU read-side critical section. The pointer can later be safely
  71  * dereferenced within the critical section.
  72  *
  73  * This ensures that the pointer copy is invariant thorough the whole critical
  74  * section.
  75  *
  76  * Inserts memory barriers on architectures that require them (currently only
  77  * Alpha) and documents which pointers are protected by RCU.
  78  *
  79  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  80  */
  81
  82 #define _rcu_dereference(p)     ({                                      \
  83                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  84                                 smp_read_barrier_depends();             \
  85                                 (_________p1);                          \
  86                                 })
  87
  88 /*
  89  * This code section can only be included in LGPL 2.1 compatible source code.
  90  * See below for the function call wrappers which can be used in code meant to
  91  * be only linked with the Userspace RCU library. This comes with a small
  92  * performance degradation on the read-side due to the added function calls.
  93  * This is required to permit relinking with newer versions of the library.
  94  */
  95
  96 /*
  97  * The signal number used by the RCU library can be overridden with
  98  * -DSIGURCU= when compiling the library.
  99  */
 100 #ifndef SIGURCU
 101 #define SIGURCU SIGUSR1
 102 #endif
 103
 104 /*
 105  * If a reader is really non-cooperative and refuses to commit its
 106  * urcu_active_readers count to memory (there is no barrier in the reader
 107  * per-se), kick it after a few loops waiting for it.
 108  */
 109 #define KICK_READER_LOOPS 10000
 110
 111 #ifdef DEBUG_YIELD
 112 #include <sched.h>
 113 #include <time.h>
 114 #include <pthread.h>
 115 #include <unistd.h>
 116
 117 #define YIELD_READ      (1 << 0)
 118 #define YIELD_WRITE     (1 << 1)
 119
 120 /* maximum sleep delay, in us */
 121 #define MAX_SLEEP 50
 122
 123 extern unsigned int yield_active;
 124 extern unsigned int __thread rand_yield;
 125
 126 static inline void debug_yield_read(void)
 127 {
 128         if (yield_active & YIELD_READ)
 129                 if (rand_r(&rand_yield) & 0x1)
 130                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 131 }
 132
 133 static inline void debug_yield_write(void)
 134 {
 135         if (yield_active & YIELD_WRITE)
 136                 if (rand_r(&rand_yield) & 0x1)
 137                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 138 }
 139
 140 static inline void debug_yield_init(void)
 141 {
 142         rand_yield = time(NULL) ^ pthread_self();
 143 }
 144 #else
 145 static inline void debug_yield_read(void)
 146 {
 147 }
 148
 149 static inline void debug_yield_write(void)
 150 {
 151 }
 152
 153 static inline void debug_yield_init(void)
 154 {
 155
 156 }
 157 #endif
 158
 159 static inline void reader_barrier()
 160 {
 161         smp_mb();
 162 }
 163
 164 /*
 165  * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
 166  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 167  */
 168 #define RCU_GP_COUNT            (1UL << 0)
 169 /* Use the amount of bits equal to half of the architecture long size */
 170 #define RCU_GP_CTR_BIT          (1UL << (sizeof(long) << 2))
 171 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_BIT - 1)
 172
 173 /*
 174  * Global quiescent period counter with low-order bits unused.
 175  * Using a int rather than a char to eliminate false register dependencies
 176  * causing stalls on some architectures.
 177  */
 178 extern long urcu_gp_ctr;
 179
 180 extern long __thread urcu_active_readers;
 181
 182 static inline int rcu_old_gp_ongoing(long *value)
 183 {
 184         if (value == NULL)
 185                 return 0;
 186
 187         return LOAD_SHARED(*value) & 1;
 188 }
 189
 190 static inline void _rcu_read_lock(void)
 191 {
 192 }
 193
 194 static inline void _rcu_read_unlock(void)
 195 {
 196 }
 197
 198 static inline void _rcu_quiescent_state(void)
 199 {
 200         smp_mb();
 201         urcu_active_readers = ACCESS_ONCE(urcu_gp_ctr) + 1;
 202         smp_mb();
 203 }
 204
 205 static inline void _rcu_thread_offline(void)
 206 {
 207         smp_mb();
 208         urcu_active_readers = ACCESS_ONCE(urcu_gp_ctr);
 209 }
 210
 211 static inline void _rcu_thread_online(void)
 212 {
 213         urcu_active_readers = ACCESS_ONCE(urcu_gp_ctr) + 1;
 214         smp_mb();
 215 }
 216
 217 /**
 218  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 219  * meant to be read by RCU read-side critical sections. Returns the assigned
 220  * value.
 221  *
 222  * Documents which pointers will be dereferenced by RCU read-side critical
 223  * sections and adds the required memory barriers on architectures requiring
 224  * them. It also makes sure the compiler does not reorder code initializing the
 225  * data structure before its publication.
 226  *
 227  * Should match rcu_dereference_pointer().
 228  */
 229
 230 #define _rcu_assign_pointer(p, v)                       \
 231         ({                                              \
 232                 if (!__builtin_constant_p(v) ||         \
 233                     ((v) != NULL))                      \
 234                         wmb();                          \
 235                 STORE_SHARED(p, v);                     \
 236         })
 237
 238 /**
 239  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 240  * pointer to the data structure, which can be safely freed after waiting for a
 241  * quiescent state using synchronize_rcu().
 242  */
 243
 244 #define _rcu_xchg_pointer(p, v)                         \
 245         ({                                              \
 246                 if (!__builtin_constant_p(v) ||         \
 247                     ((v) != NULL))                      \
 248                         wmb();                          \
 249                 xchg(p, v);                             \
 250         })
 251
 252 /*
 253  * Exchanges the pointer and waits for quiescent state.
 254  * The pointer returned can be freed.
 255  */
 256 #define _rcu_publish_content(p, v)                      \
 257         ({                                              \
 258                 void *oldptr;                           \
 259                 oldptr = _rcu_xchg_pointer(p, v);       \
 260                 synchronize_rcu();                      \
 261                 oldptr;                                 \
 262         })
 263
 264 extern void synchronize_rcu(void);
 265
 266 /*
 267  * Reader thread registration.
 268  */
 269 extern void rcu_register_thread(void);
 270 extern void rcu_unregister_thread(void);
 271
 272 #endif /* _URCU_QSBR_H */