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                 void *client_ctx);
 155
 156 extern
 157 void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf,
 158                                  enum switch_mode mode);
 159
 160 extern
 161 void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config *config,
 162                                    struct lib_ring_buffer *buf,
 163                                    struct channel *chan,
 164                                    unsigned long offset,
 165                                    unsigned long commit_count,
 166                                    unsigned long idx,
 167                                    u64 tsc);
 168
 169 extern
 170 void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf);
 171 extern
 172 void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf);
 173
 174 /* Buffer write helpers */
 175
 176 static inline
 177 void lib_ring_buffer_reserve_push_reader(struct lib_ring_buffer *buf,
 178                                          struct channel *chan,
 179                                          unsigned long offset)
 180 {
 181         unsigned long consumed_old, consumed_new;
 182
 183         do {
 184                 consumed_old = atomic_long_read(&buf->consumed);
 185                 /*
 186                  * If buffer is in overwrite mode, push the reader consumed
 187                  * count if the write position has reached it and we are not
 188                  * at the first iteration (don't push the reader farther than
 189                  * the writer). This operation can be done concurrently by many
 190                  * writers in the same buffer, the writer being at the farthest
 191                  * write position sub-buffer index in the buffer being the one
 192                  * which will win this loop.
 193                  */
 194                 if (unlikely(subbuf_trunc(offset, chan)
 195                               - subbuf_trunc(consumed_old, chan)
 196                              >= chan->backend.buf_size))
 197                         consumed_new = subbuf_align(consumed_old, chan);
 198                 else
 199                         return;
 200         } while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
 201                                               consumed_new) != consumed_old));
 202 }
 203
 204 static inline
 205 int lib_ring_buffer_pending_data(const struct lib_ring_buffer_config *config,
 206                                  struct lib_ring_buffer *buf,
 207                                  struct channel *chan)
 208 {
 209         return !!subbuf_offset(v_read(config, &buf->offset), chan);
 210 }
 211
 212 static inline
 213 unsigned long lib_ring_buffer_get_data_size(const struct lib_ring_buffer_config *config,
 214                                             struct lib_ring_buffer *buf,
 215                                             unsigned long idx)
 216 {
 217         return subbuffer_get_data_size(config, &buf->backend, idx);
 218 }
 219
 220 /*
 221  * Check if all space reservation in a buffer have been committed. This helps
 222  * knowing if an execution context is nested (for per-cpu buffers only).
 223  * This is a very specific ftrace use-case, so we keep this as "internal" API.
 224  */
 225 static inline
 226 int lib_ring_buffer_reserve_committed(const struct lib_ring_buffer_config *config,
 227                                       struct lib_ring_buffer *buf,
 228                                       struct channel *chan)
 229 {
 230         unsigned long offset, idx, commit_count;
 231
 232         CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 233         CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 234
 235         /*
 236          * Read offset and commit count in a loop so they are both read
 237          * atomically wrt interrupts. By deal with interrupt concurrency by
 238          * restarting both reads if the offset has been pushed. Note that given
 239          * we only have to deal with interrupt concurrency here, an interrupt
 240          * modifying the commit count will also modify "offset", so it is safe
 241          * to only check for offset modifications.
 242          */
 243         do {
 244                 offset = v_read(config, &buf->offset);
 245                 idx = subbuf_index(offset, chan);
 246                 commit_count = v_read(config, &buf->commit_hot[idx].cc);
 247         } while (offset != v_read(config, &buf->offset));
 248
 249         return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 250                      - (commit_count & chan->commit_count_mask) == 0);
 251 }
 252
 253 /*
 254  * Receive end of subbuffer TSC as parameter. It has been read in the
 255  * space reservation loop of either reserve or switch, which ensures it
 256  * progresses monotonically with event records in the buffer. Therefore,
 257  * it ensures that the end timestamp of a subbuffer is <= begin
 258  * timestamp of the following subbuffers.
 259  */
 260 static inline
 261 void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
 262                                    struct lib_ring_buffer *buf,
 263                                    struct channel *chan,
 264                                    unsigned long offset,
 265                                    unsigned long commit_count,
 266                                    unsigned long idx,
 267                                    u64 tsc)
 268 {
 269         unsigned long old_commit_count = commit_count
 270                                          - chan->backend.subbuf_size;
 271
 272         /* Check if all commits have been done */
 273         if (unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 274                      - (old_commit_count & chan->commit_count_mask) == 0))
 275                 lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
 276                         commit_count, idx, tsc);
 277 }
 278
 279 /*
 280  * lib_ring_buffer_write_commit_counter
 281  *
 282  * For flight recording. must be called after commit.
 283  * This function increments the subbuffer's commit_seq counter each time the
 284  * commit count reaches back the reserve offset (modulo subbuffer size). It is
 285  * useful for crash dump.
 286  */
 287 static inline
 288 void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *config,
 289                                           struct lib_ring_buffer *buf,
 290                                           struct channel *chan,
 291                                           unsigned long buf_offset,
 292                                           unsigned long commit_count,
 293                                           struct commit_counters_hot *cc_hot)
 294 {
 295         unsigned long commit_seq_old;
 296
 297         if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 298                 return;
 299
 300         /*
 301          * subbuf_offset includes commit_count_mask. We can simply
 302          * compare the offsets within the subbuffer without caring about
 303          * buffer full/empty mismatch because offset is never zero here
 304          * (subbuffer header and record headers have non-zero length).
 305          */
 306         if (unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 307                 return;
 308
 309         commit_seq_old = v_read(config, &cc_hot->seq);
 310         if (likely((long) (commit_seq_old - commit_count) < 0))
 311                 v_set(config, &cc_hot->seq, commit_count);
 312 }
 313
 314 extern int lib_ring_buffer_create(struct lib_ring_buffer *buf,
 315                                   struct channel_backend *chanb, int cpu);
 316 extern void lib_ring_buffer_free(struct lib_ring_buffer *buf);
 317
 318 /* Keep track of trap nesting inside ring buffer code */
 319 DECLARE_PER_CPU(unsigned int, lib_ring_buffer_nesting);
 320
 321 #endif /* _LIB_RING_BUFFER_FRONTEND_INTERNAL_H */