libringbuffer/frontend_internal.h

   1 #ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
   2 #define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
   3
   4 /*
   5  * libringbuffer/frontend_internal.h
   6  *
   7  * Ring Buffer Library Synchronization Header (internal helpers).
   8  *
   9  * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  10  *
  11  * This library is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU Lesser General Public
  13  * License as published by the Free Software Foundation; only
  14  * version 2.1 of the License.
  15  *
  16  * This library is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  19  * Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public
  22  * License along with this library; if not, write to the Free Software
  23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  24  *
  25  *
  26  * Author:
  27  *      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  28  *
  29  * See ring_buffer_frontend.c for more information on wait-free algorithms.
  30  *
  31  * Dual LGPL v2.1/GPL v2 license.
  32  */
  33
  34 #include <urcu/compiler.h>
  35 #include <urcu/tls-compat.h>
  36 #include <signal.h>
  37 #include <pthread.h>
  38
  39 #include <lttng/ringbuffer-config.h>
  40 #include "backend_types.h"
  41 #include "frontend_types.h"
  42 #include "shm.h"
  43
  44 /* Buffer offset macros */
  45
  46 /* buf_trunc mask selects only the buffer number. */
  47 static inline
  48 unsigned long buf_trunc(unsigned long offset, struct channel *chan)
  49 {
  50         return offset & ~(chan->backend.buf_size - 1);
  51
  52 }
  53
  54 /* Select the buffer number value (counter). */
  55 static inline
  56 unsigned long buf_trunc_val(unsigned long offset, struct channel *chan)
  57 {
  58         return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
  59 }
  60
  61 /* buf_offset mask selects only the offset within the current buffer. */
  62 static inline
  63 unsigned long buf_offset(unsigned long offset, struct channel *chan)
  64 {
  65         return offset & (chan->backend.buf_size - 1);
  66 }
  67
  68 /* subbuf_offset mask selects the offset within the current subbuffer. */
  69 static inline
  70 unsigned long subbuf_offset(unsigned long offset, struct channel *chan)
  71 {
  72         return offset & (chan->backend.subbuf_size - 1);
  73 }
  74
  75 /* subbuf_trunc mask selects the subbuffer number. */
  76 static inline
  77 unsigned long subbuf_trunc(unsigned long offset, struct channel *chan)
  78 {
  79         return offset & ~(chan->backend.subbuf_size - 1);
  80 }
  81
  82 /* subbuf_align aligns the offset to the next subbuffer. */
  83 static inline
  84 unsigned long subbuf_align(unsigned long offset, struct channel *chan)
  85 {
  86         return (offset + chan->backend.subbuf_size)
  87                & ~(chan->backend.subbuf_size - 1);
  88 }
  89
  90 /* subbuf_index returns the index of the current subbuffer within the buffer. */
  91 static inline
  92 unsigned long subbuf_index(unsigned long offset, struct channel *chan)
  93 {
  94         return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
  95 }
  96
  97 /*
  98  * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
  99  * bits from the last TSC read. When overflows are detected, the full 64-bit
 100  * timestamp counter should be written in the record header. Reads and writes
 101  * last_tsc atomically.
 102  */
 103
 104 #if (CAA_BITS_PER_LONG == 32)
 105 static inline
 106 void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
 107                    struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
 108 {
 109         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 110                 return;
 111
 112         /*
 113          * Ensure the compiler performs this update in a single instruction.
 114          */
 115         v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
 116 }
 117
 118 static inline
 119 int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
 120                       struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
 121 {
 122         unsigned long tsc_shifted;
 123
 124         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 125                 return 0;
 126
 127         tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
 128         if (caa_unlikely(tsc_shifted
 129                      - (unsigned long)v_read(config, &buf->last_tsc)))
 130                 return 1;
 131         else
 132                 return 0;
 133 }
 134 #else
 135 static inline
 136 void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
 137                    struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
 138 {
 139         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 140                 return;
 141
 142         v_set(config, &buf->last_tsc, (unsigned long)tsc);
 143 }
 144
 145 static inline
 146 int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
 147                       struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
 148 {
 149         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 150                 return 0;
 151
 152         if (caa_unlikely((tsc - v_read(config, &buf->last_tsc))
 153                      >> config->tsc_bits))
 154                 return 1;
 155         else
 156                 return 0;
 157 }
 158 #endif
 159
 160 extern
 161 int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx);
 162
 163 extern
 164 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer *buf,
 165                                  enum switch_mode mode,
 166                                  struct lttng_ust_shm_handle *handle);
 167
 168 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config *config,
 169                                    struct lttng_ust_lib_ring_buffer *buf,
 170                                    struct channel *chan,
 171                                    unsigned long offset,
 172                                    unsigned long commit_count,
 173                                    unsigned long idx,
 174                                    struct lttng_ust_shm_handle *handle,
 175                                    uint64_t tsc);
 176
 177 /* Buffer write helpers */
 178
 179 static inline
 180 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
 181                                          struct channel *chan,
 182                                          unsigned long offset)
 183 {
 184         unsigned long consumed_old, consumed_new;
 185
 186         do {
 187                 consumed_old = uatomic_read(&buf->consumed);
 188                 /*
 189                  * If buffer is in overwrite mode, push the reader consumed
 190                  * count if the write position has reached it and we are not
 191                  * at the first iteration (don't push the reader farther than
 192                  * the writer). This operation can be done concurrently by many
 193                  * writers in the same buffer, the writer being at the farthest
 194                  * write position sub-buffer index in the buffer being the one
 195                  * which will win this loop.
 196                  */
 197                 if (caa_unlikely(subbuf_trunc(offset, chan)
 198                               - subbuf_trunc(consumed_old, chan)
 199                              >= chan->backend.buf_size))
 200                         consumed_new = subbuf_align(consumed_old, chan);
 201                 else
 202                         return;
 203         } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
 204                                               consumed_new) != consumed_old));
 205 }
 206
 207 static inline
 208 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
 209                                   struct lttng_ust_shm_handle *handle)
 210 {
 211         struct channel *chan;
 212         const struct lttng_ust_lib_ring_buffer_config *config;
 213         unsigned long offset, consumed_old, consumed_new;
 214
 215         chan = shmp(handle, buf->backend.chan);
 216         if (!chan)
 217                 return;
 218         config = &chan->backend.config;
 219
 220         do {
 221                 offset = v_read(config, &buf->offset);
 222                 consumed_old = uatomic_read(&buf->consumed);
 223                 if (caa_unlikely(subbuf_trunc(offset, chan)
 224                               - subbuf_trunc(consumed_old, chan)
 225                              > 0))
 226                         consumed_new = subbuf_trunc(offset, chan);
 227                 else
 228                         return;
 229         } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
 230                                               consumed_new) != consumed_old));
 231 }
 232
 233 static inline
 234 int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config *config,
 235                                  struct lttng_ust_lib_ring_buffer *buf,
 236                                  struct channel *chan)
 237 {
 238         return !!subbuf_offset(v_read(config, &buf->offset), chan);
 239 }
 240
 241 static inline
 242 unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
 243                                             struct lttng_ust_lib_ring_buffer *buf,
 244                                             unsigned long idx,
 245                                             struct lttng_ust_shm_handle *handle)
 246 {
 247         return subbuffer_get_data_size(config, &buf->backend, idx, handle);
 248 }
 249
 250 /*
 251  * Check if all space reservation in a buffer have been committed. This helps
 252  * knowing if an execution context is nested (for per-cpu buffers only).
 253  * This is a very specific ftrace use-case, so we keep this as "internal" API.
 254  */
 255 static inline
 256 int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config *config,
 257                                       struct lttng_ust_lib_ring_buffer *buf,
 258                                       struct channel *chan,
 259                                       struct lttng_ust_shm_handle *handle)
 260 {
 261         unsigned long offset, idx, commit_count;
 262         struct commit_counters_hot *cc_hot = shmp_index(handle, buf->commit_hot, idx);
 263
 264         CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 265         CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 266
 267         if (caa_unlikely(!cc_hot))
 268                 return 0;
 269
 270         /*
 271          * Read offset and commit count in a loop so they are both read
 272          * atomically wrt interrupts. By deal with interrupt concurrency by
 273          * restarting both reads if the offset has been pushed. Note that given
 274          * we only have to deal with interrupt concurrency here, an interrupt
 275          * modifying the commit count will also modify "offset", so it is safe
 276          * to only check for offset modifications.
 277          */
 278         do {
 279                 offset = v_read(config, &buf->offset);
 280                 idx = subbuf_index(offset, chan);
 281                 commit_count = v_read(config, &cc_hot->cc);
 282         } while (offset != v_read(config, &buf->offset));
 283
 284         return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 285                      - (commit_count & chan->commit_count_mask) == 0);
 286 }
 287
 288 /*
 289  * Receive end of subbuffer TSC as parameter. It has been read in the
 290  * space reservation loop of either reserve or switch, which ensures it
 291  * progresses monotonically with event records in the buffer. Therefore,
 292  * it ensures that the end timestamp of a subbuffer is <= begin
 293  * timestamp of the following subbuffers.
 294  */
 295 static inline
 296 void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config *config,
 297                                    struct lttng_ust_lib_ring_buffer *buf,
 298                                    struct channel *chan,
 299                                    unsigned long offset,
 300                                    unsigned long commit_count,
 301                                    unsigned long idx,
 302                                    struct lttng_ust_shm_handle *handle,
 303                                    uint64_t tsc)
 304 {
 305         unsigned long old_commit_count = commit_count
 306                                          - chan->backend.subbuf_size;
 307
 308         /* Check if all commits have been done */
 309         if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 310                      - (old_commit_count & chan->commit_count_mask) == 0))
 311                 lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
 312                         commit_count, idx, handle, tsc);
 313 }
 314
 315 /*
 316  * lib_ring_buffer_write_commit_counter
 317  *
 318  * For flight recording. must be called after commit.
 319  * This function increments the subbuffer's commit_seq counter each time the
 320  * commit count reaches back the reserve offset (modulo subbuffer size). It is
 321  * useful for crash dump.
 322  */
 323 static inline
 324 void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config *config,
 325                                           struct lttng_ust_lib_ring_buffer *buf,
 326                                           struct channel *chan,
 327                                           unsigned long buf_offset,
 328                                           unsigned long commit_count,
 329                                           struct lttng_ust_shm_handle *handle,
 330                                           struct commit_counters_hot *cc_hot)
 331 {
 332         unsigned long commit_seq_old;
 333
 334         if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 335                 return;
 336
 337         /*
 338          * subbuf_offset includes commit_count_mask. We can simply
 339          * compare the offsets within the subbuffer without caring about
 340          * buffer full/empty mismatch because offset is never zero here
 341          * (subbuffer header and record headers have non-zero length).
 342          */
 343         if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 344                 return;
 345
 346         commit_seq_old = v_read(config, &cc_hot->seq);
 347         if (caa_likely((long) (commit_seq_old - commit_count) < 0))
 348                 v_set(config, &cc_hot->seq, commit_count);
 349 }
 350
 351 extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer *buf,
 352                                   struct channel_backend *chanb, int cpu,
 353                                   struct lttng_ust_shm_handle *handle,
 354                                   struct shm_object *shmobj);
 355 extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer *buf,
 356                                  struct lttng_ust_shm_handle *handle);
 357
 358 /* Keep track of trap nesting inside ring buffer code */
 359 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting);
 360
 361 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */