1 #ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
2 #define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
5 * libringbuffer/frontend_internal.h
7 * Ring Buffer Library Synchronization Header (internal helpers).
9 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.
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.
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
27 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
29 * See ring_buffer_frontend.c for more information on wait-free algorithms.
31 * Dual LGPL v2.1/GPL v2 license.
34 #include <urcu/compiler.h>
35 #include <urcu/tls-compat.h>
40 #include <lttng/ringbuffer-config.h>
41 #include "backend_types.h"
42 #include "frontend_types.h"
45 /* Buffer offset macros */
47 /* buf_trunc mask selects only the buffer number. */
49 unsigned long buf_trunc(unsigned long offset
, struct channel
*chan
)
51 return offset
& ~(chan
->backend
.buf_size
- 1);
55 /* Select the buffer number value (counter). */
57 unsigned long buf_trunc_val(unsigned long offset
, struct channel
*chan
)
59 return buf_trunc(offset
, chan
) >> chan
->backend
.buf_size_order
;
62 /* buf_offset mask selects only the offset within the current buffer. */
64 unsigned long buf_offset(unsigned long offset
, struct channel
*chan
)
66 return offset
& (chan
->backend
.buf_size
- 1);
69 /* subbuf_offset mask selects the offset within the current subbuffer. */
71 unsigned long subbuf_offset(unsigned long offset
, struct channel
*chan
)
73 return offset
& (chan
->backend
.subbuf_size
- 1);
76 /* subbuf_trunc mask selects the subbuffer number. */
78 unsigned long subbuf_trunc(unsigned long offset
, struct channel
*chan
)
80 return offset
& ~(chan
->backend
.subbuf_size
- 1);
83 /* subbuf_align aligns the offset to the next subbuffer. */
85 unsigned long subbuf_align(unsigned long offset
, struct channel
*chan
)
87 return (offset
+ chan
->backend
.subbuf_size
)
88 & ~(chan
->backend
.subbuf_size
- 1);
91 /* subbuf_index returns the index of the current subbuffer within the buffer. */
93 unsigned long subbuf_index(unsigned long offset
, struct channel
*chan
)
95 return buf_offset(offset
, chan
) >> chan
->backend
.subbuf_size_order
;
99 * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
100 * bits from the last TSC read. When overflows are detected, the full 64-bit
101 * timestamp counter should be written in the record header. Reads and writes
102 * last_tsc atomically.
105 #if (CAA_BITS_PER_LONG == 32)
107 void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config
*config
,
108 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
110 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
114 * Ensure the compiler performs this update in a single instruction.
116 v_set(config
, &buf
->last_tsc
, (unsigned long)(tsc
>> config
->tsc_bits
));
120 int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config
*config
,
121 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
123 unsigned long tsc_shifted
;
125 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
128 tsc_shifted
= (unsigned long)(tsc
>> config
->tsc_bits
);
129 if (caa_unlikely(tsc_shifted
130 - (unsigned long)v_read(config
, &buf
->last_tsc
)))
137 void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config
*config
,
138 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
140 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
143 v_set(config
, &buf
->last_tsc
, (unsigned long)tsc
);
147 int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config
*config
,
148 struct lttng_ust_lib_ring_buffer
*buf
, uint64_t tsc
)
150 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
153 if (caa_unlikely((tsc
- v_read(config
, &buf
->last_tsc
))
154 >> config
->tsc_bits
))
162 int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
166 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer
*buf
,
167 enum switch_mode mode
,
168 struct lttng_ust_shm_handle
*handle
);
170 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config
*config
,
171 struct lttng_ust_lib_ring_buffer
*buf
,
172 struct channel
*chan
,
173 unsigned long offset
,
174 unsigned long commit_count
,
176 struct lttng_ust_shm_handle
*handle
,
179 /* Buffer write helpers */
182 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer
*buf
,
183 struct channel
*chan
,
184 unsigned long offset
)
186 unsigned long consumed_old
, consumed_new
;
189 consumed_old
= uatomic_read(&buf
->consumed
);
191 * If buffer is in overwrite mode, push the reader consumed
192 * count if the write position has reached it and we are not
193 * at the first iteration (don't push the reader farther than
194 * the writer). This operation can be done concurrently by many
195 * writers in the same buffer, the writer being at the farthest
196 * write position sub-buffer index in the buffer being the one
197 * which will win this loop.
199 if (caa_unlikely(subbuf_trunc(offset
, chan
)
200 - subbuf_trunc(consumed_old
, chan
)
201 >= chan
->backend
.buf_size
))
202 consumed_new
= subbuf_align(consumed_old
, chan
);
205 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
206 consumed_new
) != consumed_old
));
210 * Move consumed position to the beginning of subbuffer in which the
211 * write offset is. Should only be used on ring buffers that are not
212 * actively being written into, because clear_reader does not take into
213 * account the commit counters when moving the consumed position, which
214 * can make concurrent trace producers or consumers observe consumed
215 * position further than the write offset, which breaks ring buffer
216 * algorithm guarantees.
219 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer
*buf
,
220 struct lttng_ust_shm_handle
*handle
)
222 struct channel
*chan
;
223 const struct lttng_ust_lib_ring_buffer_config
*config
;
224 unsigned long offset
, consumed_old
, consumed_new
;
226 chan
= shmp(handle
, buf
->backend
.chan
);
229 config
= &chan
->backend
.config
;
232 offset
= v_read(config
, &buf
->offset
);
233 consumed_old
= uatomic_read(&buf
->consumed
);
234 CHAN_WARN_ON(chan
, (long) (subbuf_trunc(offset
, chan
)
235 - subbuf_trunc(consumed_old
, chan
))
237 consumed_new
= subbuf_trunc(offset
, chan
);
238 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
239 consumed_new
) != consumed_old
));
243 int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config
*config
,
244 struct lttng_ust_lib_ring_buffer
*buf
,
245 struct channel
*chan
)
247 return !!subbuf_offset(v_read(config
, &buf
->offset
), chan
);
251 unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
252 struct lttng_ust_lib_ring_buffer
*buf
,
254 struct lttng_ust_shm_handle
*handle
)
256 return subbuffer_get_data_size(config
, &buf
->backend
, idx
, handle
);
260 * Check if all space reservation in a buffer have been committed. This helps
261 * knowing if an execution context is nested (for per-cpu buffers only).
262 * This is a very specific ftrace use-case, so we keep this as "internal" API.
265 int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config
*config
,
266 struct lttng_ust_lib_ring_buffer
*buf
,
267 struct channel
*chan
,
268 struct lttng_ust_shm_handle
*handle
)
270 unsigned long offset
, idx
, commit_count
;
271 struct commit_counters_hot
*cc_hot
;
273 CHAN_WARN_ON(chan
, config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
);
274 CHAN_WARN_ON(chan
, config
->sync
!= RING_BUFFER_SYNC_PER_CPU
);
277 * Read offset and commit count in a loop so they are both read
278 * atomically wrt interrupts. By deal with interrupt concurrency by
279 * restarting both reads if the offset has been pushed. Note that given
280 * we only have to deal with interrupt concurrency here, an interrupt
281 * modifying the commit count will also modify "offset", so it is safe
282 * to only check for offset modifications.
285 offset
= v_read(config
, &buf
->offset
);
286 idx
= subbuf_index(offset
, chan
);
287 cc_hot
= shmp_index(handle
, buf
->commit_hot
, idx
);
288 if (caa_unlikely(!cc_hot
))
290 commit_count
= v_read(config
, &cc_hot
->cc
);
291 } while (offset
!= v_read(config
, &buf
->offset
));
293 return ((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
294 - (commit_count
& chan
->commit_count_mask
) == 0);
298 * Receive end of subbuffer TSC as parameter. It has been read in the
299 * space reservation loop of either reserve or switch, which ensures it
300 * progresses monotonically with event records in the buffer. Therefore,
301 * it ensures that the end timestamp of a subbuffer is <= begin
302 * timestamp of the following subbuffers.
305 void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
*config
,
306 struct lttng_ust_lib_ring_buffer
*buf
,
307 struct channel
*chan
,
308 unsigned long offset
,
309 unsigned long commit_count
,
311 struct lttng_ust_shm_handle
*handle
,
314 unsigned long old_commit_count
= commit_count
315 - chan
->backend
.subbuf_size
;
317 /* Check if all commits have been done */
318 if (caa_unlikely((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
319 - (old_commit_count
& chan
->commit_count_mask
) == 0))
320 lib_ring_buffer_check_deliver_slow(config
, buf
, chan
, offset
,
321 commit_count
, idx
, handle
, tsc
);
325 * lib_ring_buffer_write_commit_counter
327 * For flight recording. must be called after commit.
328 * This function increments the subbuffer's commit_seq counter each time the
329 * commit count reaches back the reserve offset (modulo subbuffer size). It is
330 * useful for crash dump.
333 void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config
*config
,
334 struct lttng_ust_lib_ring_buffer
*buf
,
335 struct channel
*chan
,
336 unsigned long buf_offset
,
337 unsigned long commit_count
,
338 struct lttng_ust_shm_handle
*handle
,
339 struct commit_counters_hot
*cc_hot
)
341 unsigned long commit_seq_old
;
343 if (config
->oops
!= RING_BUFFER_OOPS_CONSISTENCY
)
347 * subbuf_offset includes commit_count_mask. We can simply
348 * compare the offsets within the subbuffer without caring about
349 * buffer full/empty mismatch because offset is never zero here
350 * (subbuffer header and record headers have non-zero length).
352 if (caa_unlikely(subbuf_offset(buf_offset
- commit_count
, chan
)))
355 commit_seq_old
= v_read(config
, &cc_hot
->seq
);
356 if (caa_likely((long) (commit_seq_old
- commit_count
) < 0))
357 v_set(config
, &cc_hot
->seq
, commit_count
);
360 extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer
*buf
,
361 struct channel_backend
*chanb
, int cpu
,
362 struct lttng_ust_shm_handle
*handle
,
363 struct shm_object
*shmobj
);
364 extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer
*buf
,
365 struct lttng_ust_shm_handle
*handle
);
367 /* Keep track of trap nesting inside ring buffer code */
368 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting
);
370 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */