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 int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
28 struct channel_backend
*chan
,
30 struct lttng_ust_shm_handle
*handle
,
31 struct shm_object
*shmobj
)
32 __attribute__((visibility("hidden")));
34 void channel_backend_unregister_notifiers(struct channel_backend
*chanb
)
35 __attribute__((visibility("hidden")));
37 void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend
*bufb
)
38 __attribute__((visibility("hidden")));
40 int channel_backend_init(struct channel_backend
*chanb
,
42 const struct lttng_ust_lib_ring_buffer_config
*config
,
44 size_t num_subbuf
, struct lttng_ust_shm_handle
*handle
,
45 const int *stream_fds
)
46 __attribute__((visibility("hidden")));
48 void channel_backend_free(struct channel_backend
*chanb
,
49 struct lttng_ust_shm_handle
*handle
)
50 __attribute__((visibility("hidden")));
52 void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
53 struct lttng_ust_shm_handle
*handle
)
54 __attribute__((visibility("hidden")));
56 void channel_backend_reset(struct channel_backend
*chanb
)
57 __attribute__((visibility("hidden")));
59 int lib_ring_buffer_backend_init(void)
60 __attribute__((visibility("hidden")));
62 void lib_ring_buffer_backend_exit(void)
63 __attribute__((visibility("hidden")));
65 extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
66 size_t offset
, const void *src
, size_t len
,
68 __attribute__((visibility("hidden")));
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(
126 const struct lttng_ust_lib_ring_buffer_config
*config
__attribute__((unused
)),
127 unsigned long id
, unsigned long offset
)
129 return (id
& SB_ID_OFFSET_MASK
) == (offset
<< SB_ID_OFFSET_SHIFT
);
133 unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
136 if (config
->mode
== RING_BUFFER_OVERWRITE
)
137 return id
& SB_ID_INDEX_MASK
;
143 unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
146 if (config
->mode
== RING_BUFFER_OVERWRITE
)
147 return !!(id
& SB_ID_NOREF_MASK
);
153 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
157 void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
160 if (config
->mode
== RING_BUFFER_OVERWRITE
)
161 *id
|= SB_ID_NOREF_MASK
;
165 void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
166 unsigned long *id
, unsigned long offset
)
170 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
172 tmp
&= ~SB_ID_OFFSET_MASK
;
173 tmp
|= offset
<< SB_ID_OFFSET_SHIFT
;
174 tmp
|= SB_ID_NOREF_MASK
;
175 /* Volatile store, read concurrently by readers. */
176 CMM_ACCESS_ONCE(*id
) = tmp
;
180 /* No volatile access, since already used locally */
182 void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
185 if (config
->mode
== RING_BUFFER_OVERWRITE
)
186 *id
&= ~SB_ID_NOREF_MASK
;
190 * For overwrite mode, cap the number of subbuffers per buffer to:
191 * 2^16 on 32-bit architectures
192 * 2^32 on 64-bit architectures
193 * This is required to fit in the index part of the ID. Return 0 on success,
197 int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
198 unsigned long num_subbuf
)
200 if (config
->mode
== RING_BUFFER_OVERWRITE
)
201 return (num_subbuf
> (1UL << HALF_ULONG_BITS
)) ? -EPERM
: 0;
207 int lib_ring_buffer_backend_get_pages(const struct lttng_ust_lib_ring_buffer_config
*config
,
208 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
209 struct lttng_ust_lib_ring_buffer_backend_pages
**backend_pages
)
211 struct lttng_ust_lib_ring_buffer_ctx_private
*ctx_private
= ctx
->priv
;
212 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &ctx_private
->buf
->backend
;
213 struct channel_backend
*chanb
= &ctx_private
->chan
->backend
;
214 struct lttng_ust_shm_handle
*handle
= ctx_private
->chan
->handle
;
216 size_t offset
= ctx_private
->buf_offset
;
217 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
218 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
219 unsigned long sb_bindex
, id
;
220 struct lttng_ust_lib_ring_buffer_backend_pages
*_backend_pages
;
222 offset
&= chanb
->buf_size
- 1;
223 sbidx
= offset
>> chanb
->subbuf_size_order
;
224 wsb
= shmp_index(handle
, bufb
->buf_wsb
, sbidx
);
225 if (caa_unlikely(!wsb
))
228 sb_bindex
= subbuffer_id_get_index(config
, id
);
229 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
230 if (caa_unlikely(!rpages
))
232 CHAN_WARN_ON(ctx_private
->chan
,
233 config
->mode
== RING_BUFFER_OVERWRITE
234 && subbuffer_id_is_noref(config
, id
));
235 _backend_pages
= shmp(handle
, rpages
->shmp
);
236 if (caa_unlikely(!_backend_pages
))
238 *backend_pages
= _backend_pages
;
242 /* Get backend pages from cache. */
244 struct lttng_ust_lib_ring_buffer_backend_pages
*
245 lib_ring_buffer_get_backend_pages_from_ctx(
246 const struct lttng_ust_lib_ring_buffer_config
*config
__attribute__((unused
)),
247 struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
249 return ctx
->priv
->backend_pages
;
253 * The ring buffer can count events recorded and overwritten per buffer,
254 * but it is disabled by default due to its performance overhead.
256 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
258 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
259 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
260 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
261 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
263 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
265 backend_pages
= lib_ring_buffer_get_backend_pages_from_ctx(config
, ctx
);
266 if (caa_unlikely(!backend_pages
)) {
267 if (lib_ring_buffer_backend_get_pages(config
, ctx
, &backend_pages
))
270 v_inc(config
, &backend_pages
->records_commit
);
272 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
274 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
__attribute__((unused
)),
275 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
__attribute__((unused
)),
276 struct lttng_ust_lib_ring_buffer_backend
*bufb
__attribute__((unused
)),
277 unsigned long idx
__attribute__((unused
)),
278 struct lttng_ust_shm_handle
*handle
__attribute__((unused
)))
281 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
284 * Reader has exclusive subbuffer access for record consumption. No need to
285 * perform the decrement atomically.
288 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
289 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
290 struct lttng_ust_shm_handle
*handle
)
292 unsigned long sb_bindex
;
293 struct lttng_ust_lib_ring_buffer_channel
*chan
;
294 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
295 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
297 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
298 chan
= shmp(handle
, bufb
->chan
);
301 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
304 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
307 CHAN_WARN_ON(chan
, !v_read(config
, &backend_pages
->records_unread
));
308 /* Non-atomic decrement protected by exclusive subbuffer access */
309 _v_dec(config
, &backend_pages
->records_unread
);
310 v_inc(config
, &bufb
->records_read
);
314 unsigned long subbuffer_get_records_count(
315 const struct lttng_ust_lib_ring_buffer_config
*config
,
316 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
318 struct lttng_ust_shm_handle
*handle
)
320 unsigned long sb_bindex
;
321 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
322 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
323 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
325 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
328 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
329 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
332 backend_pages
= shmp(handle
, rpages
->shmp
);
335 return v_read(config
, &backend_pages
->records_commit
);
339 * Must be executed at subbuffer delivery when the writer has _exclusive_
340 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
341 * lib_ring_buffer_get_records_count() must be called to get the records
342 * count before this function, because it resets the records_commit
346 unsigned long subbuffer_count_records_overrun(
347 const struct lttng_ust_lib_ring_buffer_config
*config
,
348 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
350 struct lttng_ust_shm_handle
*handle
)
352 unsigned long overruns
, sb_bindex
;
353 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
354 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
355 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
357 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
360 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
361 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
364 backend_pages
= shmp(handle
, rpages
->shmp
);
367 overruns
= v_read(config
, &backend_pages
->records_unread
);
368 v_set(config
, &backend_pages
->records_unread
,
369 v_read(config
, &backend_pages
->records_commit
));
370 v_set(config
, &backend_pages
->records_commit
, 0);
376 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
377 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
379 unsigned long data_size
,
380 struct lttng_ust_shm_handle
*handle
)
382 unsigned long sb_bindex
;
383 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
384 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
385 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
387 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
390 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
391 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
394 backend_pages
= shmp(handle
, rpages
->shmp
);
397 backend_pages
->data_size
= data_size
;
401 unsigned long subbuffer_get_read_data_size(
402 const struct lttng_ust_lib_ring_buffer_config
*config
,
403 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
404 struct lttng_ust_shm_handle
*handle
)
406 unsigned long sb_bindex
;
407 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
408 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
410 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
411 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
414 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
417 return backend_pages
->data_size
;
421 unsigned long subbuffer_get_data_size(
422 const struct lttng_ust_lib_ring_buffer_config
*config
,
423 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
425 struct lttng_ust_shm_handle
*handle
)
427 unsigned long sb_bindex
;
428 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
429 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
430 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
432 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
435 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
436 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
439 backend_pages
= shmp(handle
, rpages
->shmp
);
442 return backend_pages
->data_size
;
446 void subbuffer_inc_packet_count(
447 const struct lttng_ust_lib_ring_buffer_config
*config
__attribute__((unused
)),
448 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
449 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
451 struct lttng_ust_lib_ring_buffer_backend_counts
*counts
;
453 counts
= shmp_index(handle
, bufb
->buf_cnt
, idx
);
460 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
464 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
465 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
467 struct lttng_ust_shm_handle
*handle
)
469 unsigned long id
, new_id
;
470 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
472 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
476 * Performing a volatile access to read the sb_pages, because we want to
477 * read a coherent version of the pointer and the associated noref flag.
479 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
482 id
= CMM_ACCESS_ONCE(wsb
->id
);
484 /* This check is called on the fast path for each record. */
485 if (caa_likely(!subbuffer_id_is_noref(config
, id
))) {
487 * Store after load dependency ordering the writes to
488 * the subbuffer after load and test of the noref flag
489 * matches the memory barrier implied by the cmpxchg()
490 * in update_read_sb_index().
492 return; /* Already writing to this buffer */
495 subbuffer_id_clear_noref(config
, &new_id
);
496 new_id
= uatomic_cmpxchg(&wsb
->id
, id
, new_id
);
497 if (caa_likely(new_id
== id
))
504 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
508 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
509 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
510 unsigned long idx
, unsigned long offset
,
511 struct lttng_ust_shm_handle
*handle
)
513 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
514 struct lttng_ust_lib_ring_buffer_channel
*chan
;
516 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
519 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
523 * Because ring_buffer_set_noref() is only called by a single thread
524 * (the one which updated the cc_sb value), there are no concurrent
525 * updates to take care of: other writers have not updated cc_sb, so
526 * they cannot set the noref flag, and concurrent readers cannot modify
527 * the pointer because the noref flag is not set yet.
528 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
529 * to the subbuffer before this set noref operation.
530 * subbuffer_set_noref() uses a volatile store to deal with concurrent
531 * readers of the noref flag.
533 chan
= shmp(handle
, bufb
->chan
);
536 CHAN_WARN_ON(chan
, subbuffer_id_is_noref(config
, wsb
->id
));
538 * Memory barrier that ensures counter stores are ordered before set
542 subbuffer_id_set_noref_offset(config
, &wsb
->id
, offset
);
546 * update_read_sb_index - Read-side subbuffer index update.
549 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
550 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
551 struct channel_backend
*chanb
__attribute__((unused
)),
552 unsigned long consumed_idx
,
553 unsigned long consumed_count
,
554 struct lttng_ust_shm_handle
*handle
)
556 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
557 unsigned long old_id
, new_id
;
559 wsb
= shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
);
560 if (caa_unlikely(!wsb
))
563 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
564 struct lttng_ust_lib_ring_buffer_channel
*chan
;
567 * Exchange the target writer subbuffer with our own unused
568 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
569 * old_wpage, because the value read will be confirmed by the
570 * following cmpxchg().
573 if (caa_unlikely(!subbuffer_id_is_noref(config
, old_id
)))
576 * Make sure the offset count we are expecting matches the one
577 * indicated by the writer.
579 if (caa_unlikely(!subbuffer_id_compare_offset(config
, old_id
,
582 chan
= shmp(handle
, bufb
->chan
);
583 if (caa_unlikely(!chan
))
585 CHAN_WARN_ON(chan
, !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
586 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
588 new_id
= uatomic_cmpxchg(&wsb
->id
, old_id
, bufb
->buf_rsb
.id
);
589 if (caa_unlikely(old_id
!= new_id
))
591 bufb
->buf_rsb
.id
= new_id
;
593 /* No page exchange, use the writer page directly */
594 bufb
->buf_rsb
.id
= wsb
->id
;
599 #ifndef inline_memcpy
600 #define inline_memcpy(dest, src, n) memcpy(dest, src, n)
604 void lttng_inline_memcpy(void *dest
, const void *src
,
606 __attribute__((always_inline
));
608 void lttng_inline_memcpy(void *dest
, const void *src
,
613 *(uint8_t *) dest
= *(const uint8_t *) src
;
616 *(uint16_t *) dest
= *(const uint16_t *) src
;
619 *(uint32_t *) dest
= *(const uint32_t *) src
;
622 *(uint64_t *) dest
= *(const uint64_t *) src
;
625 inline_memcpy(dest
, src
, len
);
630 * Use the architecture-specific memcpy implementation for constant-sized
631 * inputs, but rely on an inline memcpy for length statically unknown.
632 * The function call to memcpy is just way too expensive for a fast path.
634 #define lib_ring_buffer_do_copy(config, dest, src, len) \
636 size_t __len = (len); \
637 if (__builtin_constant_p(len)) \
638 memcpy(dest, src, __len); \
640 lttng_inline_memcpy(dest, src, __len); \
644 * write len bytes to dest with c
647 void lib_ring_buffer_do_memset(char *dest
, char c
, unsigned long len
)
651 for (i
= 0; i
< len
; i
++)
655 /* arch-agnostic implementation */
657 static inline int lttng_ust_fls(unsigned int x
)
663 if (!(x
& 0xFFFF0000U
)) {
667 if (!(x
& 0xFF000000U
)) {
671 if (!(x
& 0xF0000000U
)) {
675 if (!(x
& 0xC0000000U
)) {
679 if (!(x
& 0x80000000U
)) {
680 /* No need to bit shift on last operation */
686 static inline int get_count_order(unsigned int count
)
690 order
= lttng_ust_fls(count
) - 1;
691 if (count
& (count
- 1))
696 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */