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
);
164 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer
*buf
,
165 enum switch_mode mode
,
166 struct lttng_ust_shm_handle
*handle
);
168 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config
*config
,
169 struct lttng_ust_lib_ring_buffer
*buf
,
170 struct channel
*chan
,
171 unsigned long offset
,
172 unsigned long commit_count
,
174 struct lttng_ust_shm_handle
*handle
,
177 /* Buffer write helpers */
180 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer
*buf
,
181 struct channel
*chan
,
182 unsigned long offset
)
184 unsigned long consumed_old
, consumed_new
;
187 consumed_old
= uatomic_read(&buf
->consumed
);
189 * If buffer is in overwrite mode, push the reader consumed
190 * count if the write position has reached it and we are not
191 * at the first iteration (don't push the reader farther than
192 * the writer). This operation can be done concurrently by many
193 * writers in the same buffer, the writer being at the farthest
194 * write position sub-buffer index in the buffer being the one
195 * which will win this loop.
197 if (caa_unlikely(subbuf_trunc(offset
, chan
)
198 - subbuf_trunc(consumed_old
, chan
)
199 >= chan
->backend
.buf_size
))
200 consumed_new
= subbuf_align(consumed_old
, chan
);
203 } while (caa_unlikely(uatomic_cmpxchg(&buf
->consumed
, consumed_old
,
204 consumed_new
) != consumed_old
));
208 int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config
*config
,
209 struct lttng_ust_lib_ring_buffer
*buf
,
210 struct channel
*chan
)
212 return !!subbuf_offset(v_read(config
, &buf
->offset
), chan
);
216 unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
217 struct lttng_ust_lib_ring_buffer
*buf
,
219 struct lttng_ust_shm_handle
*handle
)
221 return subbuffer_get_data_size(config
, &buf
->backend
, idx
, handle
);
225 * Check if all space reservation in a buffer have been committed. This helps
226 * knowing if an execution context is nested (for per-cpu buffers only).
227 * This is a very specific ftrace use-case, so we keep this as "internal" API.
230 int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config
*config
,
231 struct lttng_ust_lib_ring_buffer
*buf
,
232 struct channel
*chan
,
233 struct lttng_ust_shm_handle
*handle
)
235 unsigned long offset
, idx
, commit_count
;
237 CHAN_WARN_ON(chan
, config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
);
238 CHAN_WARN_ON(chan
, config
->sync
!= RING_BUFFER_SYNC_PER_CPU
);
241 * Read offset and commit count in a loop so they are both read
242 * atomically wrt interrupts. By deal with interrupt concurrency by
243 * restarting both reads if the offset has been pushed. Note that given
244 * we only have to deal with interrupt concurrency here, an interrupt
245 * modifying the commit count will also modify "offset", so it is safe
246 * to only check for offset modifications.
249 offset
= v_read(config
, &buf
->offset
);
250 idx
= subbuf_index(offset
, chan
);
251 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, idx
)->cc
);
252 } while (offset
!= v_read(config
, &buf
->offset
));
254 return ((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
255 - (commit_count
& chan
->commit_count_mask
) == 0);
259 * Receive end of subbuffer TSC as parameter. It has been read in the
260 * space reservation loop of either reserve or switch, which ensures it
261 * progresses monotonically with event records in the buffer. Therefore,
262 * it ensures that the end timestamp of a subbuffer is <= begin
263 * timestamp of the following subbuffers.
266 void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
*config
,
267 struct lttng_ust_lib_ring_buffer
*buf
,
268 struct channel
*chan
,
269 unsigned long offset
,
270 unsigned long commit_count
,
272 struct lttng_ust_shm_handle
*handle
,
275 unsigned long old_commit_count
= commit_count
276 - chan
->backend
.subbuf_size
;
278 /* Check if all commits have been done */
279 if (caa_unlikely((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
280 - (old_commit_count
& chan
->commit_count_mask
) == 0))
281 lib_ring_buffer_check_deliver_slow(config
, buf
, chan
, offset
,
282 commit_count
, idx
, handle
, tsc
);
286 * lib_ring_buffer_write_commit_counter
288 * For flight recording. must be called after commit.
289 * This function increments the subbuffer's commit_seq counter each time the
290 * commit count reaches back the reserve offset (modulo subbuffer size). It is
291 * useful for crash dump.
294 void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config
*config
,
295 struct lttng_ust_lib_ring_buffer
*buf
,
296 struct channel
*chan
,
298 unsigned long buf_offset
,
299 unsigned long commit_count
,
300 struct lttng_ust_shm_handle
*handle
)
302 unsigned long commit_seq_old
;
304 if (config
->oops
!= RING_BUFFER_OOPS_CONSISTENCY
)
308 * subbuf_offset includes commit_count_mask. We can simply
309 * compare the offsets within the subbuffer without caring about
310 * buffer full/empty mismatch because offset is never zero here
311 * (subbuffer header and record headers have non-zero length).
313 if (caa_unlikely(subbuf_offset(buf_offset
- commit_count
, chan
)))
316 commit_seq_old
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, idx
)->seq
);
317 while ((long) (commit_seq_old
- commit_count
) < 0)
318 commit_seq_old
= v_cmpxchg(config
, &shmp_index(handle
, buf
->commit_hot
, idx
)->seq
,
319 commit_seq_old
, commit_count
);
322 extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer
*buf
,
323 struct channel_backend
*chanb
, int cpu
,
324 struct lttng_ust_shm_handle
*handle
,
325 struct shm_object
*shmobj
);
326 extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer
*buf
,
327 struct lttng_ust_shm_handle
*handle
);
329 /* Keep track of trap nesting inside ring buffer code */
330 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting
);
332 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */