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 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
207 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
208 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
210 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
212 backend_pages
= lib_ring_buffer_get_backend_pages_from_ctx(config
, ctx
);
213 if (caa_unlikely(!backend_pages
)) {
214 if (lib_ring_buffer_backend_get_pages(config
, ctx
, &backend_pages
))
217 v_inc(config
, &backend_pages
->records_commit
);
219 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
221 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
222 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
223 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
224 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
227 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
230 * Reader has exclusive subbuffer access for record consumption. No need to
231 * perform the decrement atomically.
234 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
235 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
236 struct lttng_ust_shm_handle
*handle
)
238 unsigned long sb_bindex
;
239 struct channel
*chan
;
240 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
241 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
243 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
244 chan
= shmp(handle
, bufb
->chan
);
247 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
250 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
253 CHAN_WARN_ON(chan
, !v_read(config
, &backend_pages
->records_unread
));
254 /* Non-atomic decrement protected by exclusive subbuffer access */
255 _v_dec(config
, &backend_pages
->records_unread
);
256 v_inc(config
, &bufb
->records_read
);
260 unsigned long subbuffer_get_records_count(
261 const struct lttng_ust_lib_ring_buffer_config
*config
,
262 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
264 struct lttng_ust_shm_handle
*handle
)
266 unsigned long sb_bindex
;
267 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
268 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
269 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
271 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
274 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
275 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
278 backend_pages
= shmp(handle
, rpages
->shmp
);
281 return v_read(config
, &backend_pages
->records_commit
);
285 * Must be executed at subbuffer delivery when the writer has _exclusive_
286 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
287 * lib_ring_buffer_get_records_count() must be called to get the records
288 * count before this function, because it resets the records_commit
292 unsigned long subbuffer_count_records_overrun(
293 const struct lttng_ust_lib_ring_buffer_config
*config
,
294 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
296 struct lttng_ust_shm_handle
*handle
)
298 unsigned long overruns
, sb_bindex
;
299 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
300 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
301 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
303 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
306 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
307 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
310 backend_pages
= shmp(handle
, rpages
->shmp
);
313 overruns
= v_read(config
, &backend_pages
->records_unread
);
314 v_set(config
, &backend_pages
->records_unread
,
315 v_read(config
, &backend_pages
->records_commit
));
316 v_set(config
, &backend_pages
->records_commit
, 0);
322 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
323 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
325 unsigned long data_size
,
326 struct lttng_ust_shm_handle
*handle
)
328 unsigned long sb_bindex
;
329 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
330 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
331 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
333 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
336 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
337 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
340 backend_pages
= shmp(handle
, rpages
->shmp
);
343 backend_pages
->data_size
= data_size
;
347 unsigned long subbuffer_get_read_data_size(
348 const struct lttng_ust_lib_ring_buffer_config
*config
,
349 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
350 struct lttng_ust_shm_handle
*handle
)
352 unsigned long sb_bindex
;
353 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
354 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
356 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
357 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
360 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
363 return backend_pages
->data_size
;
367 unsigned long subbuffer_get_data_size(
368 const struct lttng_ust_lib_ring_buffer_config
*config
,
369 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
371 struct lttng_ust_shm_handle
*handle
)
373 unsigned long sb_bindex
;
374 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
375 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
376 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
378 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
381 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
382 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
385 backend_pages
= shmp(handle
, rpages
->shmp
);
388 return backend_pages
->data_size
;
392 void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config
*config
,
393 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
394 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
396 struct lttng_ust_lib_ring_buffer_backend_counts
*counts
;
398 counts
= shmp_index(handle
, bufb
->buf_cnt
, idx
);
405 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
409 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
410 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
412 struct lttng_ust_shm_handle
*handle
)
414 unsigned long id
, new_id
;
415 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
417 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
421 * Performing a volatile access to read the sb_pages, because we want to
422 * read a coherent version of the pointer and the associated noref flag.
424 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
427 id
= CMM_ACCESS_ONCE(wsb
->id
);
429 /* This check is called on the fast path for each record. */
430 if (caa_likely(!subbuffer_id_is_noref(config
, id
))) {
432 * Store after load dependency ordering the writes to
433 * the subbuffer after load and test of the noref flag
434 * matches the memory barrier implied by the cmpxchg()
435 * in update_read_sb_index().
437 return; /* Already writing to this buffer */
440 subbuffer_id_clear_noref(config
, &new_id
);
441 new_id
= uatomic_cmpxchg(&wsb
->id
, id
, new_id
);
442 if (caa_likely(new_id
== id
))
449 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
453 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
454 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
455 unsigned long idx
, unsigned long offset
,
456 struct lttng_ust_shm_handle
*handle
)
458 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
459 struct channel
*chan
;
461 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
464 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
468 * Because ring_buffer_set_noref() is only called by a single thread
469 * (the one which updated the cc_sb value), there are no concurrent
470 * updates to take care of: other writers have not updated cc_sb, so
471 * they cannot set the noref flag, and concurrent readers cannot modify
472 * the pointer because the noref flag is not set yet.
473 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
474 * to the subbuffer before this set noref operation.
475 * subbuffer_set_noref() uses a volatile store to deal with concurrent
476 * readers of the noref flag.
478 chan
= shmp(handle
, bufb
->chan
);
481 CHAN_WARN_ON(chan
, subbuffer_id_is_noref(config
, wsb
->id
));
483 * Memory barrier that ensures counter stores are ordered before set
487 subbuffer_id_set_noref_offset(config
, &wsb
->id
, offset
);
491 * update_read_sb_index - Read-side subbuffer index update.
494 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
495 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
496 struct channel_backend
*chanb
,
497 unsigned long consumed_idx
,
498 unsigned long consumed_count
,
499 struct lttng_ust_shm_handle
*handle
)
501 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
502 unsigned long old_id
, new_id
;
504 wsb
= shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
);
505 if (caa_unlikely(!wsb
))
508 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
509 struct channel
*chan
;
512 * Exchange the target writer subbuffer with our own unused
513 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
514 * old_wpage, because the value read will be confirmed by the
515 * following cmpxchg().
518 if (caa_unlikely(!subbuffer_id_is_noref(config
, old_id
)))
521 * Make sure the offset count we are expecting matches the one
522 * indicated by the writer.
524 if (caa_unlikely(!subbuffer_id_compare_offset(config
, old_id
,
527 chan
= shmp(handle
, bufb
->chan
);
528 if (caa_unlikely(!chan
))
530 CHAN_WARN_ON(chan
, !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
531 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
533 new_id
= uatomic_cmpxchg(&wsb
->id
, old_id
, bufb
->buf_rsb
.id
);
534 if (caa_unlikely(old_id
!= new_id
))
536 bufb
->buf_rsb
.id
= new_id
;
538 /* No page exchange, use the writer page directly */
539 bufb
->buf_rsb
.id
= wsb
->id
;
544 #ifndef inline_memcpy
545 #define inline_memcpy(dest, src, n) memcpy(dest, src, n)
549 * Use the architecture-specific memcpy implementation for constant-sized
550 * inputs, but rely on an inline memcpy for length statically unknown.
551 * The function call to memcpy is just way too expensive for a fast path.
553 #define lib_ring_buffer_do_copy(config, dest, src, len) \
555 size_t __len = (len); \
556 if (__builtin_constant_p(len)) \
557 memcpy(dest, src, __len); \
559 inline_memcpy(dest, src, __len); \
563 * write len bytes to dest with c
566 void lib_ring_buffer_do_memset(char *dest
, int c
, unsigned long len
)
570 for (i
= 0; i
< len
; i
++)
574 /* arch-agnostic implementation */
576 static inline int lttng_ust_fls(unsigned int x
)
582 if (!(x
& 0xFFFF0000U
)) {
586 if (!(x
& 0xFF000000U
)) {
590 if (!(x
& 0xF0000000U
)) {
594 if (!(x
& 0xC0000000U
)) {
598 if (!(x
& 0x80000000U
)) {
599 /* No need to bit shift on last operation */
605 static inline int get_count_order(unsigned int count
)
609 order
= lttng_ust_fls(count
) - 1;
610 if (count
& (count
- 1))
615 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */