2 * SPDX-License-Identifier: LGPL-2.1-only
4 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 * Ring buffer backend (internal helpers).
9 #ifndef _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H
10 #define _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H
15 #include <urcu/compiler.h>
17 #include <lttng/ringbuffer-context.h>
18 #include "ringbuffer-config.h"
19 #include "backend_types.h"
20 #include "frontend_types.h"
23 /* Ring buffer backend API presented to the frontend */
25 /* Ring buffer and channel backend create/free */
27 __attribute__((visibility("hidden")))
28 int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
29 struct channel_backend
*chan
,
31 struct lttng_ust_shm_handle
*handle
,
32 struct shm_object
*shmobj
);
34 __attribute__((visibility("hidden")))
35 void channel_backend_unregister_notifiers(struct channel_backend
*chanb
);
37 __attribute__((visibility("hidden")))
38 void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend
*bufb
);
40 __attribute__((visibility("hidden")))
41 int channel_backend_init(struct channel_backend
*chanb
,
43 const struct lttng_ust_lib_ring_buffer_config
*config
,
45 size_t num_subbuf
, struct lttng_ust_shm_handle
*handle
,
46 const int *stream_fds
);
48 __attribute__((visibility("hidden")))
49 void channel_backend_free(struct channel_backend
*chanb
,
50 struct lttng_ust_shm_handle
*handle
);
52 __attribute__((visibility("hidden")))
53 void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
54 struct lttng_ust_shm_handle
*handle
);
56 __attribute__((visibility("hidden")))
57 void channel_backend_reset(struct channel_backend
*chanb
);
59 __attribute__((visibility("hidden")))
60 int lib_ring_buffer_backend_init(void);
62 __attribute__((visibility("hidden")))
63 void lib_ring_buffer_backend_exit(void);
65 __attribute__((visibility("hidden")))
66 extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
67 size_t offset
, const void *src
, size_t len
,
71 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
72 * exchanged atomically.
74 * Top half word, except lowest bit, belongs to "offset", which is used to keep
75 * to count the produced buffers. For overwrite mode, this provides the
76 * consumer with the capacity to read subbuffers in order, handling the
77 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
78 * systems) concurrently with a single execution of get_subbuf (between offset
79 * sampling and subbuffer ID exchange).
82 #define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1)
84 #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
85 #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
86 #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
88 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
90 #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
91 #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
92 #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
94 * In overwrite mode: lowest half of word is used for index.
95 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
96 * In producer-consumer mode: whole word used for index.
98 #define SB_ID_INDEX_SHIFT 0
99 #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
100 #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
103 * Construct the subbuffer id from offset, index and noref. Use only the index
104 * for producer-consumer mode (offset and noref are only used in overwrite
108 unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config
*config
,
109 unsigned long offset
, unsigned long noref
,
112 if (config
->mode
== RING_BUFFER_OVERWRITE
)
113 return (offset
<< SB_ID_OFFSET_SHIFT
)
114 | (noref
<< SB_ID_NOREF_SHIFT
)
121 * Compare offset with the offset contained within id. Return 1 if the offset
122 * bits are identical, else 0.
125 int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
126 unsigned long id
, unsigned long offset
)
128 return (id
& SB_ID_OFFSET_MASK
) == (offset
<< SB_ID_OFFSET_SHIFT
);
132 unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
135 if (config
->mode
== RING_BUFFER_OVERWRITE
)
136 return id
& SB_ID_INDEX_MASK
;
142 unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
145 if (config
->mode
== RING_BUFFER_OVERWRITE
)
146 return !!(id
& SB_ID_NOREF_MASK
);
152 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
156 void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
159 if (config
->mode
== RING_BUFFER_OVERWRITE
)
160 *id
|= SB_ID_NOREF_MASK
;
164 void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
165 unsigned long *id
, unsigned long offset
)
169 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
171 tmp
&= ~SB_ID_OFFSET_MASK
;
172 tmp
|= offset
<< SB_ID_OFFSET_SHIFT
;
173 tmp
|= SB_ID_NOREF_MASK
;
174 /* Volatile store, read concurrently by readers. */
175 CMM_ACCESS_ONCE(*id
) = tmp
;
179 /* No volatile access, since already used locally */
181 void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
184 if (config
->mode
== RING_BUFFER_OVERWRITE
)
185 *id
&= ~SB_ID_NOREF_MASK
;
189 * For overwrite mode, cap the number of subbuffers per buffer to:
190 * 2^16 on 32-bit architectures
191 * 2^32 on 64-bit architectures
192 * This is required to fit in the index part of the ID. Return 0 on success,
196 int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
197 unsigned long num_subbuf
)
199 if (config
->mode
== RING_BUFFER_OVERWRITE
)
200 return (num_subbuf
> (1UL << HALF_ULONG_BITS
)) ? -EPERM
: 0;
206 int lib_ring_buffer_backend_get_pages(const struct lttng_ust_lib_ring_buffer_config
*config
,
207 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
208 struct lttng_ust_lib_ring_buffer_backend_pages
**backend_pages
)
210 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &ctx
->buf
->backend
;
211 struct channel_backend
*chanb
= &ctx
->chan
->backend
;
212 struct lttng_ust_shm_handle
*handle
= ctx
->chan
->handle
;
214 size_t offset
= ctx
->buf_offset
;
215 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
216 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
217 unsigned long sb_bindex
, id
;
218 struct lttng_ust_lib_ring_buffer_backend_pages
*_backend_pages
;
220 offset
&= chanb
->buf_size
- 1;
221 sbidx
= offset
>> chanb
->subbuf_size_order
;
222 wsb
= shmp_index(handle
, bufb
->buf_wsb
, sbidx
);
223 if (caa_unlikely(!wsb
))
226 sb_bindex
= subbuffer_id_get_index(config
, id
);
227 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
228 if (caa_unlikely(!rpages
))
230 CHAN_WARN_ON(ctx
->chan
,
231 config
->mode
== RING_BUFFER_OVERWRITE
232 && subbuffer_id_is_noref(config
, id
));
233 _backend_pages
= shmp(handle
, rpages
->shmp
);
234 if (caa_unlikely(!_backend_pages
))
236 *backend_pages
= _backend_pages
;
240 /* Get backend pages from cache. */
242 struct lttng_ust_lib_ring_buffer_backend_pages
*
243 lib_ring_buffer_get_backend_pages_from_ctx(const struct lttng_ust_lib_ring_buffer_config
*config
,
244 struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
246 return ctx
->backend_pages
;
250 * The ring buffer can count events recorded and overwritten per buffer,
251 * but it is disabled by default due to its performance overhead.
253 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
255 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
256 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
257 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
258 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
260 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
262 backend_pages
= lib_ring_buffer_get_backend_pages_from_ctx(config
, ctx
);
263 if (caa_unlikely(!backend_pages
)) {
264 if (lib_ring_buffer_backend_get_pages(config
, ctx
, &backend_pages
))
267 v_inc(config
, &backend_pages
->records_commit
);
269 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
271 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
272 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
273 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
274 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
277 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
280 * Reader has exclusive subbuffer access for record consumption. No need to
281 * perform the decrement atomically.
284 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
285 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
286 struct lttng_ust_shm_handle
*handle
)
288 unsigned long sb_bindex
;
289 struct lttng_ust_lib_ring_buffer_channel
*chan
;
290 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
291 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
293 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
294 chan
= shmp(handle
, bufb
->chan
);
297 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
300 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
303 CHAN_WARN_ON(chan
, !v_read(config
, &backend_pages
->records_unread
));
304 /* Non-atomic decrement protected by exclusive subbuffer access */
305 _v_dec(config
, &backend_pages
->records_unread
);
306 v_inc(config
, &bufb
->records_read
);
310 unsigned long subbuffer_get_records_count(
311 const struct lttng_ust_lib_ring_buffer_config
*config
,
312 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
314 struct lttng_ust_shm_handle
*handle
)
316 unsigned long sb_bindex
;
317 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
318 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
319 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
321 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
324 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
325 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
328 backend_pages
= shmp(handle
, rpages
->shmp
);
331 return v_read(config
, &backend_pages
->records_commit
);
335 * Must be executed at subbuffer delivery when the writer has _exclusive_
336 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
337 * lib_ring_buffer_get_records_count() must be called to get the records
338 * count before this function, because it resets the records_commit
342 unsigned long subbuffer_count_records_overrun(
343 const struct lttng_ust_lib_ring_buffer_config
*config
,
344 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
346 struct lttng_ust_shm_handle
*handle
)
348 unsigned long overruns
, sb_bindex
;
349 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
350 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
351 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
353 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
356 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
357 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
360 backend_pages
= shmp(handle
, rpages
->shmp
);
363 overruns
= v_read(config
, &backend_pages
->records_unread
);
364 v_set(config
, &backend_pages
->records_unread
,
365 v_read(config
, &backend_pages
->records_commit
));
366 v_set(config
, &backend_pages
->records_commit
, 0);
372 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
373 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
375 unsigned long data_size
,
376 struct lttng_ust_shm_handle
*handle
)
378 unsigned long sb_bindex
;
379 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
380 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
381 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
383 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
386 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
387 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
390 backend_pages
= shmp(handle
, rpages
->shmp
);
393 backend_pages
->data_size
= data_size
;
397 unsigned long subbuffer_get_read_data_size(
398 const struct lttng_ust_lib_ring_buffer_config
*config
,
399 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
400 struct lttng_ust_shm_handle
*handle
)
402 unsigned long sb_bindex
;
403 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
404 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
406 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
407 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
410 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
413 return backend_pages
->data_size
;
417 unsigned long subbuffer_get_data_size(
418 const struct lttng_ust_lib_ring_buffer_config
*config
,
419 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
421 struct lttng_ust_shm_handle
*handle
)
423 unsigned long sb_bindex
;
424 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
425 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
426 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
428 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
431 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
432 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
435 backend_pages
= shmp(handle
, rpages
->shmp
);
438 return backend_pages
->data_size
;
442 void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config
*config
,
443 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
444 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
446 struct lttng_ust_lib_ring_buffer_backend_counts
*counts
;
448 counts
= shmp_index(handle
, bufb
->buf_cnt
, idx
);
455 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
459 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
460 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
462 struct lttng_ust_shm_handle
*handle
)
464 unsigned long id
, new_id
;
465 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
467 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
471 * Performing a volatile access to read the sb_pages, because we want to
472 * read a coherent version of the pointer and the associated noref flag.
474 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
477 id
= CMM_ACCESS_ONCE(wsb
->id
);
479 /* This check is called on the fast path for each record. */
480 if (caa_likely(!subbuffer_id_is_noref(config
, id
))) {
482 * Store after load dependency ordering the writes to
483 * the subbuffer after load and test of the noref flag
484 * matches the memory barrier implied by the cmpxchg()
485 * in update_read_sb_index().
487 return; /* Already writing to this buffer */
490 subbuffer_id_clear_noref(config
, &new_id
);
491 new_id
= uatomic_cmpxchg(&wsb
->id
, id
, new_id
);
492 if (caa_likely(new_id
== id
))
499 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
503 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
504 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
505 unsigned long idx
, unsigned long offset
,
506 struct lttng_ust_shm_handle
*handle
)
508 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
509 struct lttng_ust_lib_ring_buffer_channel
*chan
;
511 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
514 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
518 * Because ring_buffer_set_noref() is only called by a single thread
519 * (the one which updated the cc_sb value), there are no concurrent
520 * updates to take care of: other writers have not updated cc_sb, so
521 * they cannot set the noref flag, and concurrent readers cannot modify
522 * the pointer because the noref flag is not set yet.
523 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
524 * to the subbuffer before this set noref operation.
525 * subbuffer_set_noref() uses a volatile store to deal with concurrent
526 * readers of the noref flag.
528 chan
= shmp(handle
, bufb
->chan
);
531 CHAN_WARN_ON(chan
, subbuffer_id_is_noref(config
, wsb
->id
));
533 * Memory barrier that ensures counter stores are ordered before set
537 subbuffer_id_set_noref_offset(config
, &wsb
->id
, offset
);
541 * update_read_sb_index - Read-side subbuffer index update.
544 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
545 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
546 struct channel_backend
*chanb
,
547 unsigned long consumed_idx
,
548 unsigned long consumed_count
,
549 struct lttng_ust_shm_handle
*handle
)
551 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
552 unsigned long old_id
, new_id
;
554 wsb
= shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
);
555 if (caa_unlikely(!wsb
))
558 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
559 struct lttng_ust_lib_ring_buffer_channel
*chan
;
562 * Exchange the target writer subbuffer with our own unused
563 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
564 * old_wpage, because the value read will be confirmed by the
565 * following cmpxchg().
568 if (caa_unlikely(!subbuffer_id_is_noref(config
, old_id
)))
571 * Make sure the offset count we are expecting matches the one
572 * indicated by the writer.
574 if (caa_unlikely(!subbuffer_id_compare_offset(config
, old_id
,
577 chan
= shmp(handle
, bufb
->chan
);
578 if (caa_unlikely(!chan
))
580 CHAN_WARN_ON(chan
, !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
581 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
583 new_id
= uatomic_cmpxchg(&wsb
->id
, old_id
, bufb
->buf_rsb
.id
);
584 if (caa_unlikely(old_id
!= new_id
))
586 bufb
->buf_rsb
.id
= new_id
;
588 /* No page exchange, use the writer page directly */
589 bufb
->buf_rsb
.id
= wsb
->id
;
594 #ifndef inline_memcpy
595 #define inline_memcpy(dest, src, n) memcpy(dest, src, n)
598 static inline __attribute__((always_inline
))
599 void lttng_inline_memcpy(void *dest
, const void *src
,
604 *(uint8_t *) dest
= *(const uint8_t *) src
;
607 *(uint16_t *) dest
= *(const uint16_t *) src
;
610 *(uint32_t *) dest
= *(const uint32_t *) src
;
613 *(uint64_t *) dest
= *(const uint64_t *) src
;
616 inline_memcpy(dest
, src
, len
);
621 * Use the architecture-specific memcpy implementation for constant-sized
622 * inputs, but rely on an inline memcpy for length statically unknown.
623 * The function call to memcpy is just way too expensive for a fast path.
625 #define lib_ring_buffer_do_copy(config, dest, src, len) \
627 size_t __len = (len); \
628 if (__builtin_constant_p(len)) \
629 memcpy(dest, src, __len); \
631 lttng_inline_memcpy(dest, src, __len); \
635 * write len bytes to dest with c
638 void lib_ring_buffer_do_memset(char *dest
, char c
, unsigned long len
)
642 for (i
= 0; i
< len
; i
++)
646 /* arch-agnostic implementation */
648 static inline int lttng_ust_fls(unsigned int x
)
654 if (!(x
& 0xFFFF0000U
)) {
658 if (!(x
& 0xFF000000U
)) {
662 if (!(x
& 0xF0000000U
)) {
666 if (!(x
& 0xC0000000U
)) {
670 if (!(x
& 0x80000000U
)) {
671 /* No need to bit shift on last operation */
677 static inline int get_count_order(unsigned int count
)
681 order
= lttng_ust_fls(count
) - 1;
682 if (count
& (count
- 1))
687 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */