2 * SPDX-License-Identifier: (LGPL-2.1-only or GPL-2.0-only)
4 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 * Ring Buffer Library Synchronization Header (internal helpers).
8 * See ring_buffer_frontend.c for more information on wait-free algorithms.
11 #ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
12 #define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
14 #include <urcu/compiler.h>
15 #include <urcu/tls-compat.h>
20 #include <lttng/ringbuffer-config.h>
21 #include "backend_types.h"
22 #include "frontend_types.h"
25 /* Buffer offset macros */
27 /* buf_trunc mask selects only the buffer number. */
29 unsigned long buf_trunc(unsigned long offset
, struct channel
*chan
)
31 return offset
& ~(chan
->backend
.buf_size
- 1);
35 /* Select the buffer number value (counter). */
37 unsigned long buf_trunc_val(unsigned long offset
, struct channel
*chan
)
39 return buf_trunc(offset
, chan
) >> chan
->backend
.buf_size_order
;
42 /* buf_offset mask selects only the offset within the current buffer. */
44 unsigned long buf_offset(unsigned long offset
, struct channel
*chan
)
46 return offset
& (chan
->backend
.buf_size
- 1);
49 /* subbuf_offset mask selects the offset within the current subbuffer. */
51 unsigned long subbuf_offset(unsigned long offset
, struct channel
*chan
)
53 return offset
& (chan
->backend
.subbuf_size
- 1);
56 /* subbuf_trunc mask selects the subbuffer number. */
58 unsigned long subbuf_trunc(unsigned long offset
, struct channel
*chan
)
60 return offset
& ~(chan
->backend
.subbuf_size
- 1);
63 /* subbuf_align aligns the offset to the next subbuffer. */
65 unsigned long subbuf_align(unsigned long offset
, struct channel
*chan
)
67 return (offset
+ chan
->backend
.subbuf_size
)
68 & ~(chan
->backend
.subbuf_size
- 1);
71 /* subbuf_index returns the index of the current subbuffer within the buffer. */
73 unsigned long subbuf_index(unsigned long offset
, struct channel
*chan
)
75 return buf_offset(offset
, chan
) >> chan
->backend
.subbuf_size_order
;
79 * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
80 * bits from the last TSC read. When overflows are detected, the full 64-bit
81 * timestamp counter should be written in the record header. Reads and writes
82 * last_tsc atomically.
85 #if (CAA_BITS_PER_LONG == 32)
87 void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config
*config
,
88 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
90 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
94 * Ensure the compiler performs this update in a single instruction.
96 v_set(config
, &buf
->last_tsc
, (unsigned long)(tsc
>> config
->tsc_bits
));
100 int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config
*config
,
101 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
103 unsigned long tsc_shifted
;
105 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
108 tsc_shifted
= (unsigned long)(tsc
>> config
->tsc_bits
);
109 if (caa_unlikely(tsc_shifted
110 - (unsigned long)v_read(config
, &buf
->last_tsc
)))
117 void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config
*config
,
118 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
120 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
123 v_set(config
, &buf
->last_tsc
, (unsigned long)tsc
);
127 int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config
*config
,
128 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
130 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
133 if (caa_unlikely((tsc
- v_read(config
, &buf
->last_tsc
))
134 >> config
->tsc_bits
))
141 __attribute__((visibility("hidden")))
143 int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
146 __attribute__((visibility("hidden")))
148 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer
*buf
,
149 enum switch_mode mode
,
150 struct lttng_ust_shm_handle
*handle
);
152 __attribute__((visibility("hidden")))
153 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config
*config
,
154 struct lttng_ust_lib_ring_buffer
*buf
,
155 struct channel
*chan
,
156 unsigned long offset
,
157 unsigned long commit_count
,
159 struct lttng_ust_shm_handle
*handle
,
162 /* Buffer write helpers */
165 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer
*buf
,
166 struct channel
*chan
,
167 unsigned long offset
)
169 unsigned long consumed_old
, consumed_new
;
172 consumed_old
= uatomic_read(&buf
->consumed
);
174 * If buffer is in overwrite mode, push the reader consumed
175 * count if the write position has reached it and we are not
176 * at the first iteration (don't push the reader farther than
177 * the writer). This operation can be done concurrently by many
178 * writers in the same buffer, the writer being at the farthest
179 * write position sub-buffer index in the buffer being the one
180 * which will win this loop.
182 if (caa_unlikely(subbuf_trunc(offset
, chan
)
183 - subbuf_trunc(consumed_old
, chan
)
184 >= chan
->backend
.buf_size
))
185 consumed_new
= subbuf_align(consumed_old
, chan
);
188 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
189 consumed_new
) != consumed_old
));
193 * Move consumed position to the beginning of subbuffer in which the
194 * write offset is. Should only be used on ring buffers that are not
195 * actively being written into, because clear_reader does not take into
196 * account the commit counters when moving the consumed position, which
197 * can make concurrent trace producers or consumers observe consumed
198 * position further than the write offset, which breaks ring buffer
199 * algorithm guarantees.
202 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer
*buf
,
203 struct lttng_ust_shm_handle
*handle
)
205 struct channel
*chan
;
206 const struct lttng_ust_lib_ring_buffer_config
*config
;
207 unsigned long offset
, consumed_old
, consumed_new
;
209 chan
= shmp(handle
, buf
->backend
.chan
);
212 config
= &chan
->backend
.config
;
215 offset
= v_read(config
, &buf
->offset
);
216 consumed_old
= uatomic_read(&buf
->consumed
);
217 CHAN_WARN_ON(chan
, (long) (subbuf_trunc(offset
, chan
)
218 - subbuf_trunc(consumed_old
, chan
))
220 consumed_new
= subbuf_trunc(offset
, chan
);
221 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
222 consumed_new
) != consumed_old
));
226 int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config
*config
,
227 struct lttng_ust_lib_ring_buffer
*buf
,
228 struct channel
*chan
)
230 return !!subbuf_offset(v_read(config
, &buf
->offset
), chan
);
234 unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
235 struct lttng_ust_lib_ring_buffer
*buf
,
237 struct lttng_ust_shm_handle
*handle
)
239 return subbuffer_get_data_size(config
, &buf
->backend
, idx
, handle
);
243 * Check if all space reservation in a buffer have been committed. This helps
244 * knowing if an execution context is nested (for per-cpu buffers only).
245 * This is a very specific ftrace use-case, so we keep this as "internal" API.
248 int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config
*config
,
249 struct lttng_ust_lib_ring_buffer
*buf
,
250 struct channel
*chan
,
251 struct lttng_ust_shm_handle
*handle
)
253 unsigned long offset
, idx
, commit_count
;
254 struct commit_counters_hot
*cc_hot
;
256 CHAN_WARN_ON(chan
, config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
);
257 CHAN_WARN_ON(chan
, config
->sync
!= RING_BUFFER_SYNC_PER_CPU
);
260 * Read offset and commit count in a loop so they are both read
261 * atomically wrt interrupts. By deal with interrupt concurrency by
262 * restarting both reads if the offset has been pushed. Note that given
263 * we only have to deal with interrupt concurrency here, an interrupt
264 * modifying the commit count will also modify "offset", so it is safe
265 * to only check for offset modifications.
268 offset
= v_read(config
, &buf
->offset
);
269 idx
= subbuf_index(offset
, chan
);
270 cc_hot
= shmp_index(handle
, buf
->commit_hot
, idx
);
271 if (caa_unlikely(!cc_hot
))
273 commit_count
= v_read(config
, &cc_hot
->cc
);
274 } while (offset
!= v_read(config
, &buf
->offset
));
276 return ((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
277 - (commit_count
& chan
->commit_count_mask
) == 0);
281 * Receive end of subbuffer TSC as parameter. It has been read in the
282 * space reservation loop of either reserve or switch, which ensures it
283 * progresses monotonically with event records in the buffer. Therefore,
284 * it ensures that the end timestamp of a subbuffer is <= begin
285 * timestamp of the following subbuffers.
288 void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
*config
,
289 struct lttng_ust_lib_ring_buffer
*buf
,
290 struct channel
*chan
,
291 unsigned long offset
,
292 unsigned long commit_count
,
294 struct lttng_ust_shm_handle
*handle
,
297 unsigned long old_commit_count
= commit_count
298 - chan
->backend
.subbuf_size
;
300 /* Check if all commits have been done */
301 if (caa_unlikely((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
302 - (old_commit_count
& chan
->commit_count_mask
) == 0))
303 lib_ring_buffer_check_deliver_slow(config
, buf
, chan
, offset
,
304 commit_count
, idx
, handle
, tsc
);
308 * lib_ring_buffer_write_commit_counter
310 * For flight recording. must be called after commit.
311 * This function increments the subbuffer's commit_seq counter each time the
312 * commit count reaches back the reserve offset (modulo subbuffer size). It is
313 * useful for crash dump.
316 void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config
*config
,
317 struct lttng_ust_lib_ring_buffer
*buf
,
318 struct channel
*chan
,
319 unsigned long buf_offset
,
320 unsigned long commit_count
,
321 struct lttng_ust_shm_handle
*handle
,
322 struct commit_counters_hot
*cc_hot
)
324 unsigned long commit_seq_old
;
326 if (config
->oops
!= RING_BUFFER_OOPS_CONSISTENCY
)
330 * subbuf_offset includes commit_count_mask. We can simply
331 * compare the offsets within the subbuffer without caring about
332 * buffer full/empty mismatch because offset is never zero here
333 * (subbuffer header and record headers have non-zero length).
335 if (caa_unlikely(subbuf_offset(buf_offset
- commit_count
, chan
)))
338 commit_seq_old
= v_read(config
, &cc_hot
->seq
);
339 if (caa_likely((long) (commit_seq_old
- commit_count
) < 0))
340 v_set(config
, &cc_hot
->seq
, commit_count
);
343 __attribute__((visibility("hidden")))
344 extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer
*buf
,
345 struct channel_backend
*chanb
, int cpu
,
346 struct lttng_ust_shm_handle
*handle
,
347 struct shm_object
*shmobj
);
349 __attribute__((visibility("hidden")))
350 extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer
*buf
,
351 struct lttng_ust_shm_handle
*handle
);
353 /* Keep track of trap nesting inside ring buffer code */
354 __attribute__((visibility("hidden")))
355 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting
);
357 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */