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                 void *client_ctx);
 163
 164 extern
 165 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer *buf,
 166                                  enum switch_mode mode,
 167                                  struct lttng_ust_shm_handle *handle);
 168
 169 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config *config,
 170                                    struct lttng_ust_lib_ring_buffer *buf,
 171                                    struct channel *chan,
 172                                    unsigned long offset,
 173                                    unsigned long commit_count,
 174                                    unsigned long idx,
 175                                    struct lttng_ust_shm_handle *handle,
 176                                    uint64_t tsc);
 177
 178 /* Buffer write helpers */
 179
 180 static inline
 181 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
 182                                          struct channel *chan,
 183                                          unsigned long offset)
 184 {
 185         unsigned long consumed_old, consumed_new;
 186
 187         do {
 188                 consumed_old = uatomic_read(&buf->consumed);
 189                 /*
 190                  * If buffer is in overwrite mode, push the reader consumed
 191                  * count if the write position has reached it and we are not
 192                  * at the first iteration (don't push the reader farther than
 193                  * the writer). This operation can be done concurrently by many
 194                  * writers in the same buffer, the writer being at the farthest
 195                  * write position sub-buffer index in the buffer being the one
 196                  * which will win this loop.
 197                  */
 198                 if (caa_unlikely(subbuf_trunc(offset, chan)
 199                               - subbuf_trunc(consumed_old, chan)
 200                              >= chan->backend.buf_size))
 201                         consumed_new = subbuf_align(consumed_old, chan);
 202                 else
 203                         return;
 204         } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
 205                                               consumed_new) != consumed_old));
 206 }
 207
 208 /*
 209  * Move consumed position to the beginning of subbuffer in which the
 210  * write offset is. Should only be used on ring buffers that are not
 211  * actively being written into, because clear_reader does not take into
 212  * account the commit counters when moving the consumed position, which
 213  * can make concurrent trace producers or consumers observe consumed
 214  * position further than the write offset, which breaks ring buffer
 215  * algorithm guarantees.
 216  */
 217 static inline
 218 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
 219                                   struct lttng_ust_shm_handle *handle)
 220 {
 221         struct channel *chan;
 222         const struct lttng_ust_lib_ring_buffer_config *config;
 223         unsigned long offset, consumed_old, consumed_new;
 224
 225         chan = shmp(handle, buf->backend.chan);
 226         if (!chan)
 227                 return;
 228         config = &chan->backend.config;
 229
 230         do {
 231                 offset = v_read(config, &buf->offset);
 232                 consumed_old = uatomic_read(&buf->consumed);
 233                 CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
 234                                 - subbuf_trunc(consumed_old, chan))
 235                                 < 0);
 236                 consumed_new = subbuf_trunc(offset, chan);
 237         } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
 238                                               consumed_new) != consumed_old));
 239 }
 240
 241 static inline
 242 int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config *config,
 243                                  struct lttng_ust_lib_ring_buffer *buf,
 244                                  struct channel *chan)
 245 {
 246         return !!subbuf_offset(v_read(config, &buf->offset), chan);
 247 }
 248
 249 static inline
 250 unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
 251                                             struct lttng_ust_lib_ring_buffer *buf,
 252                                             unsigned long idx,
 253                                             struct lttng_ust_shm_handle *handle)
 254 {
 255         return subbuffer_get_data_size(config, &buf->backend, idx, handle);
 256 }
 257
 258 /*
 259  * Check if all space reservation in a buffer have been committed. This helps
 260  * knowing if an execution context is nested (for per-cpu buffers only).
 261  * This is a very specific ftrace use-case, so we keep this as "internal" API.
 262  */
 263 static inline
 264 int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config *config,
 265                                       struct lttng_ust_lib_ring_buffer *buf,
 266                                       struct channel *chan,
 267                                       struct lttng_ust_shm_handle *handle)
 268 {
 269         unsigned long offset, idx, commit_count;
 270         struct commit_counters_hot *cc_hot;
 271
 272         CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 273         CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 274
 275         /*
 276          * Read offset and commit count in a loop so they are both read
 277          * atomically wrt interrupts. By deal with interrupt concurrency by
 278          * restarting both reads if the offset has been pushed. Note that given
 279          * we only have to deal with interrupt concurrency here, an interrupt
 280          * modifying the commit count will also modify "offset", so it is safe
 281          * to only check for offset modifications.
 282          */
 283         do {
 284                 offset = v_read(config, &buf->offset);
 285                 idx = subbuf_index(offset, chan);
 286                 cc_hot = shmp_index(handle, buf->commit_hot, idx);
 287                 if (caa_unlikely(!cc_hot))
 288                         return 0;
 289                 commit_count = v_read(config, &cc_hot->cc);
 290         } while (offset != v_read(config, &buf->offset));
 291
 292         return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 293                      - (commit_count & chan->commit_count_mask) == 0);
 294 }
 295
 296 /*
 297  * Receive end of subbuffer TSC as parameter. It has been read in the
 298  * space reservation loop of either reserve or switch, which ensures it
 299  * progresses monotonically with event records in the buffer. Therefore,
 300  * it ensures that the end timestamp of a subbuffer is <= begin
 301  * timestamp of the following subbuffers.
 302  */
 303 static inline
 304 void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config *config,
 305                                    struct lttng_ust_lib_ring_buffer *buf,
 306                                    struct channel *chan,
 307                                    unsigned long offset,
 308                                    unsigned long commit_count,
 309                                    unsigned long idx,
 310                                    struct lttng_ust_shm_handle *handle,
 311                                    uint64_t tsc)
 312 {
 313         unsigned long old_commit_count = commit_count
 314                                          - chan->backend.subbuf_size;
 315
 316         /* Check if all commits have been done */
 317         if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 318                      - (old_commit_count & chan->commit_count_mask) == 0))
 319                 lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
 320                         commit_count, idx, handle, tsc);
 321 }
 322
 323 /*
 324  * lib_ring_buffer_write_commit_counter
 325  *
 326  * For flight recording. must be called after commit.
 327  * This function increments the subbuffer's commit_seq counter each time the
 328  * commit count reaches back the reserve offset (modulo subbuffer size). It is
 329  * useful for crash dump.
 330  */
 331 static inline
 332 void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config *config,
 333                                           struct lttng_ust_lib_ring_buffer *buf,
 334                                           struct channel *chan,
 335                                           unsigned long buf_offset,
 336                                           unsigned long commit_count,
 337                                           struct lttng_ust_shm_handle *handle,
 338                                           struct commit_counters_hot *cc_hot)
 339 {
 340         unsigned long commit_seq_old;
 341
 342         if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 343                 return;
 344
 345         /*
 346          * subbuf_offset includes commit_count_mask. We can simply
 347          * compare the offsets within the subbuffer without caring about
 348          * buffer full/empty mismatch because offset is never zero here
 349          * (subbuffer header and record headers have non-zero length).
 350          */
 351         if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 352                 return;
 353
 354         commit_seq_old = v_read(config, &cc_hot->seq);
 355         if (caa_likely((long) (commit_seq_old - commit_count) < 0))
 356                 v_set(config, &cc_hot->seq, commit_count);
 357 }
 358
 359 extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer *buf,
 360                                   struct channel_backend *chanb, int cpu,
 361                                   struct lttng_ust_shm_handle *handle,
 362                                   struct shm_object *shmobj);
 363 extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer *buf,
 364                                  struct lttng_ust_shm_handle *handle);
 365
 366 /* Keep track of trap nesting inside ring buffer code */
 367 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting);
 368
 369 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */