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>
39 #include <lttng/ringbuffer-config.h>
40 #include "backend_types.h"
41 #include "frontend_types.h"
44 /* Buffer offset macros */
46 /* buf_trunc mask selects only the buffer number. */
48 unsigned long buf_trunc(unsigned long offset
, struct channel
*chan
)
50 return offset
& ~(chan
->backend
.buf_size
- 1);
54 /* Select the buffer number value (counter). */
56 unsigned long buf_trunc_val(unsigned long offset
, struct channel
*chan
)
58 return buf_trunc(offset
, chan
) >> chan
->backend
.buf_size_order
;
61 /* buf_offset mask selects only the offset within the current buffer. */
63 unsigned long buf_offset(unsigned long offset
, struct channel
*chan
)
65 return offset
& (chan
->backend
.buf_size
- 1);
68 /* subbuf_offset mask selects the offset within the current subbuffer. */
70 unsigned long subbuf_offset(unsigned long offset
, struct channel
*chan
)
72 return offset
& (chan
->backend
.subbuf_size
- 1);
75 /* subbuf_trunc mask selects the subbuffer number. */
77 unsigned long subbuf_trunc(unsigned long offset
, struct channel
*chan
)
79 return offset
& ~(chan
->backend
.subbuf_size
- 1);
82 /* subbuf_align aligns the offset to the next subbuffer. */
84 unsigned long subbuf_align(unsigned long offset
, struct channel
*chan
)
86 return (offset
+ chan
->backend
.subbuf_size
)
87 & ~(chan
->backend
.subbuf_size
- 1);
90 /* subbuf_index returns the index of the current subbuffer within the buffer. */
92 unsigned long subbuf_index(unsigned long offset
, struct channel
*chan
)
94 return buf_offset(offset
, chan
) >> chan
->backend
.subbuf_size_order
;
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.
104 #if (CAA_BITS_PER_LONG == 32)
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
)
109 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
113 * Ensure the compiler performs this update in a single instruction.
115 v_set(config
, &buf
->last_tsc
, (unsigned long)(tsc
>> config
->tsc_bits
));
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
)
122 unsigned long tsc_shifted
;
124 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
127 tsc_shifted
= (unsigned long)(tsc
>> config
->tsc_bits
);
128 if (caa_unlikely(tsc_shifted
129 - (unsigned long)v_read(config
, &buf
->last_tsc
)))
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
)
139 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
142 v_set(config
, &buf
->last_tsc
, (unsigned long)tsc
);
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
)
149 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
152 if (caa_unlikely((tsc
- v_read(config
, &buf
->last_tsc
))
153 >> config
->tsc_bits
))
161 int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
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
);
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
,
175 struct lttng_ust_shm_handle
*handle
,
178 /* Buffer write helpers */
181 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer
*buf
,
182 struct channel
*chan
,
183 unsigned long offset
)
185 unsigned long consumed_old
, consumed_new
;
188 consumed_old
= uatomic_read(&buf
->consumed
);
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.
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
);
204 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
205 consumed_new
) != consumed_old
));
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.
218 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer
*buf
,
219 struct lttng_ust_shm_handle
*handle
)
221 struct channel
*chan
;
222 const struct lttng_ust_lib_ring_buffer_config
*config
;
223 unsigned long offset
, consumed_old
, consumed_new
;
225 chan
= shmp(handle
, buf
->backend
.chan
);
228 config
= &chan
->backend
.config
;
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
))
236 consumed_new
= subbuf_trunc(offset
, chan
);
237 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
238 consumed_new
) != consumed_old
));
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
)
246 return !!subbuf_offset(v_read(config
, &buf
->offset
), chan
);
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
,
253 struct lttng_ust_shm_handle
*handle
)
255 return subbuffer_get_data_size(config
, &buf
->backend
, idx
, handle
);
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.
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
)
269 unsigned long offset
, idx
, commit_count
;
270 struct commit_counters_hot
*cc_hot
;
272 CHAN_WARN_ON(chan
, config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
);
273 CHAN_WARN_ON(chan
, config
->sync
!= RING_BUFFER_SYNC_PER_CPU
);
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.
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
))
289 commit_count
= v_read(config
, &cc_hot
->cc
);
290 } while (offset
!= v_read(config
, &buf
->offset
));
292 return ((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
293 - (commit_count
& chan
->commit_count_mask
) == 0);
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.
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
,
310 struct lttng_ust_shm_handle
*handle
,
313 unsigned long old_commit_count
= commit_count
314 - chan
->backend
.subbuf_size
;
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
);
324 * lib_ring_buffer_write_commit_counter
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.
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
)
340 unsigned long commit_seq_old
;
342 if (config
->oops
!= RING_BUFFER_OOPS_CONSISTENCY
)
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).
351 if (caa_unlikely(subbuf_offset(buf_offset
- commit_count
, chan
)))
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
);
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
);
366 /* Keep track of trap nesting inside ring buffer code */
367 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting
);
369 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */