lib/ringbuffer/frontend_internal.h

   1 #ifndef _LIB_RING_BUFFER_FRONTEND_INTERNAL_H
   2 #define _LIB_RING_BUFFER_FRONTEND_INTERNAL_H
   3
   4 /*
   5  * linux/ringbuffer/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  * Author:
  26  *      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  27  *
  28  * See ring_buffer_frontend.c for more information on wait-free algorithms.
  29  */
  30
  31 #include <wrapper/ringbuffer/config.h>
  32 #include <wrapper/ringbuffer/backend_types.h>
  33 #include <wrapper/ringbuffer/frontend_types.h>
  34 #include <lib/prio_heap/lttng_prio_heap.h>      /* For per-CPU read-side iterator */
  35
  36 /* Buffer offset macros */
  37
  38 /* buf_trunc mask selects only the buffer number. */
  39 static inline
  40 unsigned long buf_trunc(unsigned long offset, struct channel *chan)
  41 {
  42         return offset & ~(chan->backend.buf_size - 1);
  43
  44 }
  45
  46 /* Select the buffer number value (counter). */
  47 static inline
  48 unsigned long buf_trunc_val(unsigned long offset, struct channel *chan)
  49 {
  50         return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
  51 }
  52
  53 /* buf_offset mask selects only the offset within the current buffer. */
  54 static inline
  55 unsigned long buf_offset(unsigned long offset, struct channel *chan)
  56 {
  57         return offset & (chan->backend.buf_size - 1);
  58 }
  59
  60 /* subbuf_offset mask selects the offset within the current subbuffer. */
  61 static inline
  62 unsigned long subbuf_offset(unsigned long offset, struct channel *chan)
  63 {
  64         return offset & (chan->backend.subbuf_size - 1);
  65 }
  66
  67 /* subbuf_trunc mask selects the subbuffer number. */
  68 static inline
  69 unsigned long subbuf_trunc(unsigned long offset, struct channel *chan)
  70 {
  71         return offset & ~(chan->backend.subbuf_size - 1);
  72 }
  73
  74 /* subbuf_align aligns the offset to the next subbuffer. */
  75 static inline
  76 unsigned long subbuf_align(unsigned long offset, struct channel *chan)
  77 {
  78         return (offset + chan->backend.subbuf_size)
  79                & ~(chan->backend.subbuf_size - 1);
  80 }
  81
  82 /* subbuf_index returns the index of the current subbuffer within the buffer. */
  83 static inline
  84 unsigned long subbuf_index(unsigned long offset, struct channel *chan)
  85 {
  86         return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
  87 }
  88
  89 /*
  90  * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
  91  * bits from the last TSC read. When overflows are detected, the full 64-bit
  92  * timestamp counter should be written in the record header. Reads and writes
  93  * last_tsc atomically.
  94  */
  95
  96 #if (BITS_PER_LONG == 32)
  97 static inline
  98 void save_last_tsc(const struct lib_ring_buffer_config *config,
  99                    struct lib_ring_buffer *buf, u64 tsc)
 100 {
 101         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 102                 return;
 103
 104         /*
 105          * Ensure the compiler performs this update in a single instruction.
 106          */
 107         v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
 108 }
 109
 110 static inline
 111 int last_tsc_overflow(const struct lib_ring_buffer_config *config,
 112                       struct lib_ring_buffer *buf, u64 tsc)
 113 {
 114         unsigned long tsc_shifted;
 115
 116         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 117                 return 0;
 118
 119         tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
 120         if (unlikely(tsc_shifted
 121                      - (unsigned long)v_read(config, &buf->last_tsc)))
 122                 return 1;
 123         else
 124                 return 0;
 125 }
 126 #else
 127 static inline
 128 void save_last_tsc(const struct lib_ring_buffer_config *config,
 129                    struct lib_ring_buffer *buf, u64 tsc)
 130 {
 131         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 132                 return;
 133
 134         v_set(config, &buf->last_tsc, (unsigned long)tsc);
 135 }
 136
 137 static inline
 138 int last_tsc_overflow(const struct lib_ring_buffer_config *config,
 139                       struct lib_ring_buffer *buf, u64 tsc)
 140 {
 141         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 142                 return 0;
 143
 144         if (unlikely((tsc - v_read(config, &buf->last_tsc))
 145                      >> config->tsc_bits))
 146                 return 1;
 147         else
 148                 return 0;
 149 }
 150 #endif
 151
 152 extern
 153 int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx);
 154
 155 extern
 156 void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf,
 157                                  enum switch_mode mode);
 158
 159 extern
 160 void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config *config,
 161                                    struct lib_ring_buffer *buf,
 162                                    struct channel *chan,
 163                                    unsigned long offset,
 164                                    unsigned long commit_count,
 165                                    unsigned long idx,
 166                                    u64 tsc);
 167
 168 extern
 169 void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf);
 170
 171 /* Buffer write helpers */
 172
 173 static inline
 174 void lib_ring_buffer_reserve_push_reader(struct lib_ring_buffer *buf,
 175                                          struct channel *chan,
 176                                          unsigned long offset)
 177 {
 178         unsigned long consumed_old, consumed_new;
 179
 180         do {
 181                 consumed_old = atomic_long_read(&buf->consumed);
 182                 /*
 183                  * If buffer is in overwrite mode, push the reader consumed
 184                  * count if the write position has reached it and we are not
 185                  * at the first iteration (don't push the reader farther than
 186                  * the writer). This operation can be done concurrently by many
 187                  * writers in the same buffer, the writer being at the farthest
 188                  * write position sub-buffer index in the buffer being the one
 189                  * which will win this loop.
 190                  */
 191                 if (unlikely(subbuf_trunc(offset, chan)
 192                               - subbuf_trunc(consumed_old, chan)
 193                              >= chan->backend.buf_size))
 194                         consumed_new = subbuf_align(consumed_old, chan);
 195                 else
 196                         return;
 197         } while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
 198                                               consumed_new) != consumed_old));
 199 }
 200
 201 static inline
 202 int lib_ring_buffer_pending_data(const struct lib_ring_buffer_config *config,
 203                                  struct lib_ring_buffer *buf,
 204                                  struct channel *chan)
 205 {
 206         return !!subbuf_offset(v_read(config, &buf->offset), chan);
 207 }
 208
 209 static inline
 210 unsigned long lib_ring_buffer_get_data_size(const struct lib_ring_buffer_config *config,
 211                                             struct lib_ring_buffer *buf,
 212                                             unsigned long idx)
 213 {
 214         return subbuffer_get_data_size(config, &buf->backend, idx);
 215 }
 216
 217 /*
 218  * Check if all space reservation in a buffer have been committed. This helps
 219  * knowing if an execution context is nested (for per-cpu buffers only).
 220  * This is a very specific ftrace use-case, so we keep this as "internal" API.
 221  */
 222 static inline
 223 int lib_ring_buffer_reserve_committed(const struct lib_ring_buffer_config *config,
 224                                       struct lib_ring_buffer *buf,
 225                                       struct channel *chan)
 226 {
 227         unsigned long offset, idx, commit_count;
 228
 229         CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 230         CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 231
 232         /*
 233          * Read offset and commit count in a loop so they are both read
 234          * atomically wrt interrupts. By deal with interrupt concurrency by
 235          * restarting both reads if the offset has been pushed. Note that given
 236          * we only have to deal with interrupt concurrency here, an interrupt
 237          * modifying the commit count will also modify "offset", so it is safe
 238          * to only check for offset modifications.
 239          */
 240         do {
 241                 offset = v_read(config, &buf->offset);
 242                 idx = subbuf_index(offset, chan);
 243                 commit_count = v_read(config, &buf->commit_hot[idx].cc);
 244         } while (offset != v_read(config, &buf->offset));
 245
 246         return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 247                      - (commit_count & chan->commit_count_mask) == 0);
 248 }
 249
 250 /*
 251  * Receive end of subbuffer TSC as parameter. It has been read in the
 252  * space reservation loop of either reserve or switch, which ensures it
 253  * progresses monotonically with event records in the buffer. Therefore,
 254  * it ensures that the end timestamp of a subbuffer is <= begin
 255  * timestamp of the following subbuffers.
 256  */
 257 static inline
 258 void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
 259                                    struct lib_ring_buffer *buf,
 260                                    struct channel *chan,
 261                                    unsigned long offset,
 262                                    unsigned long commit_count,
 263                                    unsigned long idx,
 264                                    u64 tsc)
 265 {
 266         unsigned long old_commit_count = commit_count
 267                                          - chan->backend.subbuf_size;
 268
 269         /* Check if all commits have been done */
 270         if (unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 271                      - (old_commit_count & chan->commit_count_mask) == 0))
 272                 lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
 273                         commit_count, idx, tsc);
 274 }
 275
 276 /*
 277  * lib_ring_buffer_write_commit_counter
 278  *
 279  * For flight recording. must be called after commit.
 280  * This function increments the subbuffer's commit_seq counter each time the
 281  * commit count reaches back the reserve offset (modulo subbuffer size). It is
 282  * useful for crash dump.
 283  */
 284 static inline
 285 void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *config,
 286                                           struct lib_ring_buffer *buf,
 287                                           struct channel *chan,
 288                                           unsigned long buf_offset,
 289                                           unsigned long commit_count,
 290                                           struct commit_counters_hot *cc_hot)
 291 {
 292         unsigned long commit_seq_old;
 293
 294         if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 295                 return;
 296
 297         /*
 298          * subbuf_offset includes commit_count_mask. We can simply
 299          * compare the offsets within the subbuffer without caring about
 300          * buffer full/empty mismatch because offset is never zero here
 301          * (subbuffer header and record headers have non-zero length).
 302          */
 303         if (unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 304                 return;
 305
 306         commit_seq_old = v_read(config, &cc_hot->seq);
 307         if (likely((long) (commit_seq_old - commit_count) < 0))
 308                 v_set(config, &cc_hot->seq, commit_count);
 309 }
 310
 311 extern int lib_ring_buffer_create(struct lib_ring_buffer *buf,
 312                                   struct channel_backend *chanb, int cpu);
 313 extern void lib_ring_buffer_free(struct lib_ring_buffer *buf);
 314
 315 /* Keep track of trap nesting inside ring buffer code */
 316 DECLARE_PER_CPU(unsigned int, lib_ring_buffer_nesting);
 317
 318 #endif /* _LIB_RING_BUFFER_FRONTEND_INTERNAL_H */