1 #ifndef _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H
2 #define _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H
5 * libringbuffer/backend_internal.h
7 * Ring buffer backend (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 #include <urcu/compiler.h>
29 #include <lttng/ringbuffer-config.h>
30 #include "backend_types.h"
31 #include "frontend_types.h"
34 /* Ring buffer backend API presented to the frontend */
36 /* Ring buffer and channel backend create/free */
38 int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
39 struct channel_backend
*chan
, int cpu
,
40 struct lttng_ust_shm_handle
*handle
,
41 struct shm_object
*shmobj
);
42 void channel_backend_unregister_notifiers(struct channel_backend
*chanb
);
43 void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend
*bufb
);
44 int channel_backend_init(struct channel_backend
*chanb
,
46 const struct lttng_ust_lib_ring_buffer_config
*config
,
48 size_t num_subbuf
, struct lttng_ust_shm_handle
*handle
,
49 const int *stream_fds
);
50 void channel_backend_free(struct channel_backend
*chanb
,
51 struct lttng_ust_shm_handle
*handle
);
53 void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
54 struct lttng_ust_shm_handle
*handle
);
55 void channel_backend_reset(struct channel_backend
*chanb
);
57 int lib_ring_buffer_backend_init(void);
58 void lib_ring_buffer_backend_exit(void);
60 extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
61 size_t offset
, const void *src
, size_t len
,
65 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
66 * exchanged atomically.
68 * Top half word, except lowest bit, belongs to "offset", which is used to keep
69 * to count the produced buffers. For overwrite mode, this provides the
70 * consumer with the capacity to read subbuffers in order, handling the
71 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
72 * systems) concurrently with a single execution of get_subbuf (between offset
73 * sampling and subbuffer ID exchange).
76 #define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1)
78 #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
79 #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
80 #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
82 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
84 #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
85 #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
86 #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
88 * In overwrite mode: lowest half of word is used for index.
89 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
90 * In producer-consumer mode: whole word used for index.
92 #define SB_ID_INDEX_SHIFT 0
93 #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
94 #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
97 * Construct the subbuffer id from offset, index and noref. Use only the index
98 * for producer-consumer mode (offset and noref are only used in overwrite
102 unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config
*config
,
103 unsigned long offset
, unsigned long noref
,
106 if (config
->mode
== RING_BUFFER_OVERWRITE
)
107 return (offset
<< SB_ID_OFFSET_SHIFT
)
108 | (noref
<< SB_ID_NOREF_SHIFT
)
115 * Compare offset with the offset contained within id. Return 1 if the offset
116 * bits are identical, else 0.
119 int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
120 unsigned long id
, unsigned long offset
)
122 return (id
& SB_ID_OFFSET_MASK
) == (offset
<< SB_ID_OFFSET_SHIFT
);
126 unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
129 if (config
->mode
== RING_BUFFER_OVERWRITE
)
130 return id
& SB_ID_INDEX_MASK
;
136 unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
139 if (config
->mode
== RING_BUFFER_OVERWRITE
)
140 return !!(id
& SB_ID_NOREF_MASK
);
146 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
150 void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
153 if (config
->mode
== RING_BUFFER_OVERWRITE
)
154 *id
|= SB_ID_NOREF_MASK
;
158 void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
159 unsigned long *id
, unsigned long offset
)
163 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
165 tmp
&= ~SB_ID_OFFSET_MASK
;
166 tmp
|= offset
<< SB_ID_OFFSET_SHIFT
;
167 tmp
|= SB_ID_NOREF_MASK
;
168 /* Volatile store, read concurrently by readers. */
169 CMM_ACCESS_ONCE(*id
) = tmp
;
173 /* No volatile access, since already used locally */
175 void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
178 if (config
->mode
== RING_BUFFER_OVERWRITE
)
179 *id
&= ~SB_ID_NOREF_MASK
;
183 * For overwrite mode, cap the number of subbuffers per buffer to:
184 * 2^16 on 32-bit architectures
185 * 2^32 on 64-bit architectures
186 * This is required to fit in the index part of the ID. Return 0 on success,
190 int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
191 unsigned long num_subbuf
)
193 if (config
->mode
== RING_BUFFER_OVERWRITE
)
194 return (num_subbuf
> (1UL << HALF_ULONG_BITS
)) ? -EPERM
: 0;
200 * The ring buffer can count events recorded and overwritten per buffer,
201 * but it is disabled by default due to its performance overhead.
203 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
205 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
206 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
207 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
209 unsigned long sb_bindex
;
211 sb_bindex
= subbuffer_id_get_index(config
, shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
);
212 v_inc(config
, &shmp(handle
, shmp_index(handle
, bufb
->array
, sb_bindex
)->shmp
)->records_commit
);
214 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
216 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
217 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
218 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
221 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
224 * Reader has exclusive subbuffer access for record consumption. No need to
225 * perform the decrement atomically.
228 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
229 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
230 struct lttng_ust_shm_handle
*handle
)
232 unsigned long sb_bindex
;
234 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
235 CHAN_WARN_ON(shmp(handle
, bufb
->chan
),
236 !v_read(config
, &shmp(handle
, shmp_index(handle
, bufb
->array
, sb_bindex
)->shmp
)->records_unread
));
237 /* Non-atomic decrement protected by exclusive subbuffer access */
238 _v_dec(config
, &shmp(handle
, shmp_index(handle
, bufb
->array
, sb_bindex
)->shmp
)->records_unread
);
239 v_inc(config
, &bufb
->records_read
);
243 unsigned long subbuffer_get_records_count(
244 const struct lttng_ust_lib_ring_buffer_config
*config
,
245 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
247 struct lttng_ust_shm_handle
*handle
)
249 unsigned long sb_bindex
;
251 sb_bindex
= subbuffer_id_get_index(config
, shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
);
252 return v_read(config
, &shmp(handle
, shmp_index(handle
, bufb
->array
, sb_bindex
)->shmp
)->records_commit
);
256 * Must be executed at subbuffer delivery when the writer has _exclusive_
257 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
258 * lib_ring_buffer_get_records_count() must be called to get the records
259 * count before this function, because it resets the records_commit
263 unsigned long subbuffer_count_records_overrun(
264 const struct lttng_ust_lib_ring_buffer_config
*config
,
265 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
267 struct lttng_ust_shm_handle
*handle
)
269 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages
;
270 unsigned long overruns
, sb_bindex
;
272 sb_bindex
= subbuffer_id_get_index(config
, shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
);
273 pages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
274 overruns
= v_read(config
, &shmp(handle
, pages
->shmp
)->records_unread
);
275 v_set(config
, &shmp(handle
, pages
->shmp
)->records_unread
,
276 v_read(config
, &shmp(handle
, pages
->shmp
)->records_commit
));
277 v_set(config
, &shmp(handle
, pages
->shmp
)->records_commit
, 0);
283 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
284 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
286 unsigned long data_size
,
287 struct lttng_ust_shm_handle
*handle
)
289 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages
;
290 unsigned long sb_bindex
;
292 sb_bindex
= subbuffer_id_get_index(config
, shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
);
293 pages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
294 shmp(handle
, pages
->shmp
)->data_size
= data_size
;
298 unsigned long subbuffer_get_read_data_size(
299 const struct lttng_ust_lib_ring_buffer_config
*config
,
300 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
301 struct lttng_ust_shm_handle
*handle
)
303 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages
;
304 unsigned long sb_bindex
;
306 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
307 pages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
308 return shmp(handle
, pages
->shmp
)->data_size
;
312 unsigned long subbuffer_get_data_size(
313 const struct lttng_ust_lib_ring_buffer_config
*config
,
314 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
316 struct lttng_ust_shm_handle
*handle
)
318 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages
;
319 unsigned long sb_bindex
;
321 sb_bindex
= subbuffer_id_get_index(config
, shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
);
322 pages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
323 return shmp(handle
, pages
->shmp
)->data_size
;
327 void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config
*config
,
328 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
329 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
331 shmp_index(handle
, bufb
->buf_cnt
, idx
)->seq_cnt
++;
335 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
339 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
340 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
342 struct lttng_ust_shm_handle
*handle
)
344 unsigned long id
, new_id
;
346 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
350 * Performing a volatile access to read the sb_pages, because we want to
351 * read a coherent version of the pointer and the associated noref flag.
353 id
= CMM_ACCESS_ONCE(shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
);
355 /* This check is called on the fast path for each record. */
356 if (caa_likely(!subbuffer_id_is_noref(config
, id
))) {
358 * Store after load dependency ordering the writes to
359 * the subbuffer after load and test of the noref flag
360 * matches the memory barrier implied by the cmpxchg()
361 * in update_read_sb_index().
363 return; /* Already writing to this buffer */
366 subbuffer_id_clear_noref(config
, &new_id
);
367 new_id
= uatomic_cmpxchg(&shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
, id
, new_id
);
368 if (caa_likely(new_id
== id
))
375 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
379 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
380 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
381 unsigned long idx
, unsigned long offset
,
382 struct lttng_ust_shm_handle
*handle
)
384 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
388 * Because ring_buffer_set_noref() is only called by a single thread
389 * (the one which updated the cc_sb value), there are no concurrent
390 * updates to take care of: other writers have not updated cc_sb, so
391 * they cannot set the noref flag, and concurrent readers cannot modify
392 * the pointer because the noref flag is not set yet.
393 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
394 * to the subbuffer before this set noref operation.
395 * subbuffer_set_noref() uses a volatile store to deal with concurrent
396 * readers of the noref flag.
398 CHAN_WARN_ON(shmp(handle
, bufb
->chan
),
399 subbuffer_id_is_noref(config
, shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
));
401 * Memory barrier that ensures counter stores are ordered before set
405 subbuffer_id_set_noref_offset(config
, &shmp_index(handle
, bufb
->buf_wsb
, idx
)->id
, offset
);
409 * update_read_sb_index - Read-side subbuffer index update.
412 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
413 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
414 struct channel_backend
*chanb
,
415 unsigned long consumed_idx
,
416 unsigned long consumed_count
,
417 struct lttng_ust_shm_handle
*handle
)
419 unsigned long old_id
, new_id
;
421 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
423 * Exchange the target writer subbuffer with our own unused
424 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
425 * old_wpage, because the value read will be confirmed by the
426 * following cmpxchg().
428 old_id
= shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
)->id
;
429 if (caa_unlikely(!subbuffer_id_is_noref(config
, old_id
)))
432 * Make sure the offset count we are expecting matches the one
433 * indicated by the writer.
435 if (caa_unlikely(!subbuffer_id_compare_offset(config
, old_id
,
438 CHAN_WARN_ON(shmp(handle
, bufb
->chan
),
439 !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
440 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
442 new_id
= uatomic_cmpxchg(&shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
)->id
, old_id
,
444 if (caa_unlikely(old_id
!= new_id
))
446 bufb
->buf_rsb
.id
= new_id
;
448 /* No page exchange, use the writer page directly */
449 bufb
->buf_rsb
.id
= shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
)->id
;
454 #ifndef inline_memcpy
455 #define inline_memcpy(dest, src, n) memcpy(dest, src, n)
459 * Use the architecture-specific memcpy implementation for constant-sized
460 * inputs, but rely on an inline memcpy for length statically unknown.
461 * The function call to memcpy is just way too expensive for a fast path.
463 #define lib_ring_buffer_do_copy(config, dest, src, len) \
465 size_t __len = (len); \
466 if (__builtin_constant_p(len)) \
467 memcpy(dest, src, __len); \
469 inline_memcpy(dest, src, __len); \
473 * write len bytes to dest with c
476 void lib_ring_buffer_do_memset(char *dest
, int c
, unsigned long len
)
480 for (i
= 0; i
< len
; i
++)
484 /* arch-agnostic implementation */
486 static inline int lttng_ust_fls(unsigned int x
)
492 if (!(x
& 0xFFFF0000U
)) {
496 if (!(x
& 0xFF000000U
)) {
500 if (!(x
& 0xF0000000U
)) {
504 if (!(x
& 0xC0000000U
)) {
508 if (!(x
& 0x80000000U
)) {
509 /* No need to bit shift on last operation */
515 static inline int get_count_order(unsigned int count
)
519 order
= lttng_ust_fls(count
) - 1;
520 if (count
& (count
- 1))
525 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */