urcu-qsbr-static.h

   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 #include <limits.h>
  36 #include <sched.h>
  37 #include <sys/time.h>
  38
  39 #include <compiler.h>
  40 #include <arch.h>
  41
  42 /*
  43  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  44  */
  45 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  46
  47 /*
  48  * Load a data from shared memory, doing a cache flush if required.
  49  */
  50 #define LOAD_SHARED(p)                  \
  51         ({                              \
  52                 smp_rmc();              \
  53                 _LOAD_SHARED(p);        \
  54         })
  55
  56 /*
  57  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  58  */
  59 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  60
  61 /*
  62  * Store v into x, where x is located in shared memory. Performs the required
  63  * cache flush after writing. Returns v.
  64  */
  65 #define STORE_SHARED(x, v)              \
  66         ({                              \
  67                 _STORE_SHARED(x, v);    \
  68                 smp_wmc();              \
  69                 (v);                    \
  70         })
  71
  72 /**
  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.
  76  *
  77  * This ensures that the pointer copy is invariant thorough the whole critical
  78  * section.
  79  *
  80  * Inserts memory barriers on architectures that require them (currently only
  81  * Alpha) and documents which pointers are protected by RCU.
  82  *
  83  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  84  */
  85
  86 #define _rcu_dereference(p)     ({                                      \
  87                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  88                                 smp_read_barrier_depends();             \
  89                                 (_________p1);                          \
  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 /*
 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.
 104  */
 105 #define KICK_READER_LOOPS 10000
 106
 107 /*
 108  * Active attempts to check for reader Q.S. before calling sched_yield().
 109  */
 110 #define RCU_QS_ACTIVE_ATTEMPTS 100
 111
 112 #ifdef DEBUG_RCU
 113 #define rcu_assert(args...)     assert(args)
 114 #else
 115 #define rcu_assert(args...)
 116 #endif
 117
 118 #ifdef DEBUG_YIELD
 119 #include <sched.h>
 120 #include <time.h>
 121 #include <pthread.h>
 122 #include <unistd.h>
 123
 124 #define YIELD_READ      (1 << 0)
 125 #define YIELD_WRITE     (1 << 1)
 126
 127 /* maximum sleep delay, in us */
 128 #define MAX_SLEEP 50
 129
 130 extern unsigned int yield_active;
 131 extern unsigned int __thread rand_yield;
 132
 133 static inline void debug_yield_read(void)
 134 {
 135         if (yield_active & YIELD_READ)
 136                 if (rand_r(&rand_yield) & 0x1)
 137                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 138 }
 139
 140 static inline void debug_yield_write(void)
 141 {
 142         if (yield_active & YIELD_WRITE)
 143                 if (rand_r(&rand_yield) & 0x1)
 144                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 145 }
 146
 147 static inline void debug_yield_init(void)
 148 {
 149         rand_yield = time(NULL) ^ pthread_self();
 150 }
 151 #else
 152 static inline void debug_yield_read(void)
 153 {
 154 }
 155
 156 static inline void debug_yield_write(void)
 157 {
 158 }
 159
 160 static inline void debug_yield_init(void)
 161 {
 162
 163 }
 164 #endif
 165
 166 static inline void reader_barrier()
 167 {
 168         smp_mb();
 169 }
 170
 171 #define RCU_GP_ONLINE           (1UL << 0)
 172 #define RCU_GP_ONGOING          (1UL << 1)
 173 #define RCU_GP_CTR              (1UL << 2)
 174
 175 /*
 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.
 179  */
 180 extern unsigned long urcu_gp_ctr;
 181
 182 struct urcu_reader_status {
 183         unsigned long qs_gp;
 184         unsigned long gp_waiting;
 185         unsigned long qs_time_delta_usec;
 186         struct timeval qs_time_last;
 187 };
 188
 189 extern struct urcu_reader_status __thread urcu_reader_status;
 190
 191 #if (BITS_PER_LONG < 64)
 192 static inline int rcu_gp_ongoing(unsigned long *value)
 193 {
 194         unsigned long reader_gp;
 195
 196         if (value == NULL)
 197                 return 0;
 198         reader_gp = LOAD_SHARED(*value);
 199         return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
 200 }
 201 #else /* !(BITS_PER_LONG < 64) */
 202 static inline int rcu_gp_ongoing(unsigned long *value)
 203 {
 204         unsigned long reader_gp;
 205
 206         if (value == NULL)
 207                 return 0;
 208         reader_gp = LOAD_SHARED(*value);
 209         return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
 210 }
 211 #endif  /* !(BITS_PER_LONG < 64) */
 212
 213 static inline void _rcu_read_lock(void)
 214 {
 215         rcu_assert(urcu_reader_status.qs_gp);
 216 }
 217
 218 static inline void _rcu_read_unlock(void)
 219 {
 220 }
 221
 222 static inline void _rcu_quiescent_state(void)
 223 {
 224         long gp_ctr;
 225         struct timeval current_time, delta_time;
 226
 227         smp_mb();
 228         gettimeofday(&current_time, NULL);
 229         timersub(&current_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);
 232         else
 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;
 236         /*
 237          * volatile accesses can be reordered by the compiler when put in the
 238          * same expression.
 239          */
 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);
 243                 sched_yield();
 244         } else {
 245                 _STORE_SHARED(urcu_reader_status.qs_gp, gp_ctr);
 246         }
 247         smp_mb();
 248 }
 249
 250 static inline void _rcu_thread_offline(void)
 251 {
 252         smp_mb();
 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)) {
 256                 sched_yield();
 257         }
 258 }
 259
 260 static inline void _rcu_thread_online(void)
 261 {
 262         struct timeval current_time, delta_time;
 263
 264         gettimeofday(&current_time, NULL);
 265         timersub(&current_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);
 268         else
 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));
 274         smp_mb();
 275 }
 276
 277 /**
 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
 280  * value.
 281  *
 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.
 286  *
 287  * Should match rcu_dereference_pointer().
 288  */
 289
 290 #define _rcu_assign_pointer(p, v)                       \
 291         ({                                              \
 292                 if (!__builtin_constant_p(v) ||         \
 293                     ((v) != NULL))                      \
 294                         wmb();                          \
 295                 STORE_SHARED(p, v);                     \
 296         })
 297
 298 /**
 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 !).
 304  */
 305
 306 #define _rcu_cmpxchg_pointer(p, old, _new)              \
 307         ({                                              \
 308                 if (!__builtin_constant_p(_new) ||      \
 309                     ((_new) != NULL))                   \
 310                         wmb();                          \
 311                 cmpxchg(p, old, _new);                  \
 312         })
 313
 314 /**
 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().
 318  */
 319
 320 #define _rcu_xchg_pointer(p, v)                         \
 321         ({                                              \
 322                 if (!__builtin_constant_p(v) ||         \
 323                     ((v) != NULL))                      \
 324                         wmb();                          \
 325                 xchg(p, v);                             \
 326         })
 327
 328 /*
 329  * Exchanges the pointer and waits for quiescent state.
 330  * The pointer returned can be freed.
 331  */
 332 #define _rcu_publish_content(p, v)                      \
 333         ({                                              \
 334                 void *oldptr;                           \
 335                 oldptr = _rcu_xchg_pointer(p, v);       \
 336                 synchronize_rcu();                      \
 337                 oldptr;                                 \
 338         })
 339
 340 #endif /* _URCU_QSBR_STATIC_H */