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-config.h>
18 #include "backend_types.h"
19 #include "frontend_types.h"
21 #include "ust-helper.h"
23 /* Ring buffer backend API presented to the frontend */
25 /* Ring buffer and channel backend create/free */
28 int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
29 struct channel_backend
*chan
, int cpu
,
30 struct lttng_ust_shm_handle
*handle
,
31 struct shm_object
*shmobj
);
33 void channel_backend_unregister_notifiers(struct channel_backend
*chanb
);
35 void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend
*bufb
);
37 int channel_backend_init(struct channel_backend
*chanb
,
39 const struct lttng_ust_lib_ring_buffer_config
*config
,
41 size_t num_subbuf
, struct lttng_ust_shm_handle
*handle
,
42 const int *stream_fds
);
44 void channel_backend_free(struct channel_backend
*chanb
,
45 struct lttng_ust_shm_handle
*handle
);
48 void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
49 struct lttng_ust_shm_handle
*handle
);
51 void channel_backend_reset(struct channel_backend
*chanb
);
54 int lib_ring_buffer_backend_init(void);
56 void lib_ring_buffer_backend_exit(void);
59 extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
60 size_t offset
, const void *src
, size_t len
,
64 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
65 * exchanged atomically.
67 * Top half word, except lowest bit, belongs to "offset", which is used to keep
68 * to count the produced buffers. For overwrite mode, this provides the
69 * consumer with the capacity to read subbuffers in order, handling the
70 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
71 * systems) concurrently with a single execution of get_subbuf (between offset
72 * sampling and subbuffer ID exchange).
75 #define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1)
77 #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
78 #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
79 #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
81 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
83 #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
84 #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
85 #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
87 * In overwrite mode: lowest half of word is used for index.
88 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
89 * In producer-consumer mode: whole word used for index.
91 #define SB_ID_INDEX_SHIFT 0
92 #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
93 #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
96 * Construct the subbuffer id from offset, index and noref. Use only the index
97 * for producer-consumer mode (offset and noref are only used in overwrite
101 unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config
*config
,
102 unsigned long offset
, unsigned long noref
,
105 if (config
->mode
== RING_BUFFER_OVERWRITE
)
106 return (offset
<< SB_ID_OFFSET_SHIFT
)
107 | (noref
<< SB_ID_NOREF_SHIFT
)
114 * Compare offset with the offset contained within id. Return 1 if the offset
115 * bits are identical, else 0.
118 int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
119 unsigned long id
, unsigned long offset
)
121 return (id
& SB_ID_OFFSET_MASK
) == (offset
<< SB_ID_OFFSET_SHIFT
);
125 unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
128 if (config
->mode
== RING_BUFFER_OVERWRITE
)
129 return id
& SB_ID_INDEX_MASK
;
135 unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
138 if (config
->mode
== RING_BUFFER_OVERWRITE
)
139 return !!(id
& SB_ID_NOREF_MASK
);
145 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
149 void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
152 if (config
->mode
== RING_BUFFER_OVERWRITE
)
153 *id
|= SB_ID_NOREF_MASK
;
157 void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
158 unsigned long *id
, unsigned long offset
)
162 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
164 tmp
&= ~SB_ID_OFFSET_MASK
;
165 tmp
|= offset
<< SB_ID_OFFSET_SHIFT
;
166 tmp
|= SB_ID_NOREF_MASK
;
167 /* Volatile store, read concurrently by readers. */
168 CMM_ACCESS_ONCE(*id
) = tmp
;
172 /* No volatile access, since already used locally */
174 void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
177 if (config
->mode
== RING_BUFFER_OVERWRITE
)
178 *id
&= ~SB_ID_NOREF_MASK
;
182 * For overwrite mode, cap the number of subbuffers per buffer to:
183 * 2^16 on 32-bit architectures
184 * 2^32 on 64-bit architectures
185 * This is required to fit in the index part of the ID. Return 0 on success,
189 int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
190 unsigned long num_subbuf
)
192 if (config
->mode
== RING_BUFFER_OVERWRITE
)
193 return (num_subbuf
> (1UL << HALF_ULONG_BITS
)) ? -EPERM
: 0;
199 int lib_ring_buffer_backend_get_pages(const struct lttng_ust_lib_ring_buffer_config
*config
,
200 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
201 struct lttng_ust_lib_ring_buffer_backend_pages
**backend_pages
)
203 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &ctx
->buf
->backend
;
204 struct channel_backend
*chanb
= &ctx
->chan
->backend
;
205 struct lttng_ust_shm_handle
*handle
= ctx
->handle
;
207 size_t offset
= ctx
->buf_offset
;
208 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
209 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
210 unsigned long sb_bindex
, id
;
211 struct lttng_ust_lib_ring_buffer_backend_pages
*_backend_pages
;
213 offset
&= chanb
->buf_size
- 1;
214 sbidx
= offset
>> chanb
->subbuf_size_order
;
215 wsb
= shmp_index(handle
, bufb
->buf_wsb
, sbidx
);
216 if (caa_unlikely(!wsb
))
219 sb_bindex
= subbuffer_id_get_index(config
, id
);
220 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
221 if (caa_unlikely(!rpages
))
223 CHAN_WARN_ON(ctx
->chan
,
224 config
->mode
== RING_BUFFER_OVERWRITE
225 && subbuffer_id_is_noref(config
, id
));
226 _backend_pages
= shmp(handle
, rpages
->shmp
);
227 if (caa_unlikely(!_backend_pages
))
229 *backend_pages
= _backend_pages
;
233 /* Get backend pages from cache. */
235 struct lttng_ust_lib_ring_buffer_backend_pages
*
236 lib_ring_buffer_get_backend_pages_from_ctx(const struct lttng_ust_lib_ring_buffer_config
*config
,
237 struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
239 if (caa_unlikely(ctx
->ctx_len
240 < sizeof(struct lttng_ust_lib_ring_buffer_ctx
)))
242 return ctx
->backend_pages
;
246 * The ring buffer can count events recorded and overwritten per buffer,
247 * but it is disabled by default due to its performance overhead.
249 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
251 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
252 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
253 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
254 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
256 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
258 backend_pages
= lib_ring_buffer_get_backend_pages_from_ctx(config
, ctx
);
259 if (caa_unlikely(!backend_pages
)) {
260 if (lib_ring_buffer_backend_get_pages(config
, ctx
, &backend_pages
))
263 v_inc(config
, &backend_pages
->records_commit
);
265 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
267 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
268 const struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
269 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
270 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
273 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
276 * Reader has exclusive subbuffer access for record consumption. No need to
277 * perform the decrement atomically.
280 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config
*config
,
281 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
282 struct lttng_ust_shm_handle
*handle
)
284 unsigned long sb_bindex
;
285 struct channel
*chan
;
286 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
287 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
289 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
290 chan
= shmp(handle
, bufb
->chan
);
293 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
296 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
299 CHAN_WARN_ON(chan
, !v_read(config
, &backend_pages
->records_unread
));
300 /* Non-atomic decrement protected by exclusive subbuffer access */
301 _v_dec(config
, &backend_pages
->records_unread
);
302 v_inc(config
, &bufb
->records_read
);
306 unsigned long subbuffer_get_records_count(
307 const struct lttng_ust_lib_ring_buffer_config
*config
,
308 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
310 struct lttng_ust_shm_handle
*handle
)
312 unsigned long sb_bindex
;
313 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
314 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
315 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
317 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
320 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
321 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
324 backend_pages
= shmp(handle
, rpages
->shmp
);
327 return v_read(config
, &backend_pages
->records_commit
);
331 * Must be executed at subbuffer delivery when the writer has _exclusive_
332 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
333 * lib_ring_buffer_get_records_count() must be called to get the records
334 * count before this function, because it resets the records_commit
338 unsigned long subbuffer_count_records_overrun(
339 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 overruns
, sb_bindex
;
345 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
346 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
347 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
349 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
352 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
353 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
356 backend_pages
= shmp(handle
, rpages
->shmp
);
359 overruns
= v_read(config
, &backend_pages
->records_unread
);
360 v_set(config
, &backend_pages
->records_unread
,
361 v_read(config
, &backend_pages
->records_commit
));
362 v_set(config
, &backend_pages
->records_commit
, 0);
368 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config
*config
,
369 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
371 unsigned long data_size
,
372 struct lttng_ust_shm_handle
*handle
)
374 unsigned long sb_bindex
;
375 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
376 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
377 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
379 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
382 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
383 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
386 backend_pages
= shmp(handle
, rpages
->shmp
);
389 backend_pages
->data_size
= data_size
;
393 unsigned long subbuffer_get_read_data_size(
394 const struct lttng_ust_lib_ring_buffer_config
*config
,
395 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
396 struct lttng_ust_shm_handle
*handle
)
398 unsigned long sb_bindex
;
399 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages_shmp
;
400 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
402 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
403 pages_shmp
= shmp_index(handle
, bufb
->array
, sb_bindex
);
406 backend_pages
= shmp(handle
, pages_shmp
->shmp
);
409 return backend_pages
->data_size
;
413 unsigned long subbuffer_get_data_size(
414 const struct lttng_ust_lib_ring_buffer_config
*config
,
415 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
417 struct lttng_ust_shm_handle
*handle
)
419 unsigned long sb_bindex
;
420 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
421 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
422 struct lttng_ust_lib_ring_buffer_backend_pages
*backend_pages
;
424 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
427 sb_bindex
= subbuffer_id_get_index(config
, wsb
->id
);
428 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
431 backend_pages
= shmp(handle
, rpages
->shmp
);
434 return backend_pages
->data_size
;
438 void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config
*config
,
439 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
440 unsigned long idx
, struct lttng_ust_shm_handle
*handle
)
442 struct lttng_ust_lib_ring_buffer_backend_counts
*counts
;
444 counts
= shmp_index(handle
, bufb
->buf_cnt
, idx
);
451 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
455 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config
*config
,
456 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
458 struct lttng_ust_shm_handle
*handle
)
460 unsigned long id
, new_id
;
461 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
463 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
467 * Performing a volatile access to read the sb_pages, because we want to
468 * read a coherent version of the pointer and the associated noref flag.
470 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
473 id
= CMM_ACCESS_ONCE(wsb
->id
);
475 /* This check is called on the fast path for each record. */
476 if (caa_likely(!subbuffer_id_is_noref(config
, id
))) {
478 * Store after load dependency ordering the writes to
479 * the subbuffer after load and test of the noref flag
480 * matches the memory barrier implied by the cmpxchg()
481 * in update_read_sb_index().
483 return; /* Already writing to this buffer */
486 subbuffer_id_clear_noref(config
, &new_id
);
487 new_id
= uatomic_cmpxchg(&wsb
->id
, id
, new_id
);
488 if (caa_likely(new_id
== id
))
495 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
499 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config
*config
,
500 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
501 unsigned long idx
, unsigned long offset
,
502 struct lttng_ust_shm_handle
*handle
)
504 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
505 struct channel
*chan
;
507 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
510 wsb
= shmp_index(handle
, bufb
->buf_wsb
, idx
);
514 * Because ring_buffer_set_noref() is only called by a single thread
515 * (the one which updated the cc_sb value), there are no concurrent
516 * updates to take care of: other writers have not updated cc_sb, so
517 * they cannot set the noref flag, and concurrent readers cannot modify
518 * the pointer because the noref flag is not set yet.
519 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
520 * to the subbuffer before this set noref operation.
521 * subbuffer_set_noref() uses a volatile store to deal with concurrent
522 * readers of the noref flag.
524 chan
= shmp(handle
, bufb
->chan
);
527 CHAN_WARN_ON(chan
, subbuffer_id_is_noref(config
, wsb
->id
));
529 * Memory barrier that ensures counter stores are ordered before set
533 subbuffer_id_set_noref_offset(config
, &wsb
->id
, offset
);
537 * update_read_sb_index - Read-side subbuffer index update.
540 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config
*config
,
541 struct lttng_ust_lib_ring_buffer_backend
*bufb
,
542 struct channel_backend
*chanb
,
543 unsigned long consumed_idx
,
544 unsigned long consumed_count
,
545 struct lttng_ust_shm_handle
*handle
)
547 struct lttng_ust_lib_ring_buffer_backend_subbuffer
*wsb
;
548 unsigned long old_id
, new_id
;
550 wsb
= shmp_index(handle
, bufb
->buf_wsb
, consumed_idx
);
551 if (caa_unlikely(!wsb
))
554 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
555 struct channel
*chan
;
558 * Exchange the target writer subbuffer with our own unused
559 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
560 * old_wpage, because the value read will be confirmed by the
561 * following cmpxchg().
564 if (caa_unlikely(!subbuffer_id_is_noref(config
, old_id
)))
567 * Make sure the offset count we are expecting matches the one
568 * indicated by the writer.
570 if (caa_unlikely(!subbuffer_id_compare_offset(config
, old_id
,
573 chan
= shmp(handle
, bufb
->chan
);
574 if (caa_unlikely(!chan
))
576 CHAN_WARN_ON(chan
, !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
577 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
579 new_id
= uatomic_cmpxchg(&wsb
->id
, old_id
, bufb
->buf_rsb
.id
);
580 if (caa_unlikely(old_id
!= new_id
))
582 bufb
->buf_rsb
.id
= new_id
;
584 /* No page exchange, use the writer page directly */
585 bufb
->buf_rsb
.id
= wsb
->id
;
590 #ifndef inline_memcpy
591 #define inline_memcpy(dest, src, n) memcpy(dest, src, n)
594 static inline __attribute__((always_inline
))
595 void lttng_inline_memcpy(void *dest
, const void *src
,
600 *(uint8_t *) dest
= *(const uint8_t *) src
;
603 *(uint16_t *) dest
= *(const uint16_t *) src
;
606 *(uint32_t *) dest
= *(const uint32_t *) src
;
609 *(uint64_t *) dest
= *(const uint64_t *) src
;
612 inline_memcpy(dest
, src
, len
);
617 * Use the architecture-specific memcpy implementation for constant-sized
618 * inputs, but rely on an inline memcpy for length statically unknown.
619 * The function call to memcpy is just way too expensive for a fast path.
621 #define lib_ring_buffer_do_copy(config, dest, src, len) \
623 size_t __len = (len); \
624 if (__builtin_constant_p(len)) \
625 memcpy(dest, src, __len); \
627 lttng_inline_memcpy(dest, src, __len); \
631 * write len bytes to dest with c
634 void lib_ring_buffer_do_memset(char *dest
, int c
, unsigned long len
)
638 for (i
= 0; i
< len
; i
++)
642 /* arch-agnostic implementation */
644 static inline int lttng_ust_fls(unsigned int x
)
650 if (!(x
& 0xFFFF0000U
)) {
654 if (!(x
& 0xFF000000U
)) {
658 if (!(x
& 0xF0000000U
)) {
662 if (!(x
& 0xC0000000U
)) {
666 if (!(x
& 0x80000000U
)) {
667 /* No need to bit shift on last operation */
673 static inline int get_count_order(unsigned int count
)
677 order
= lttng_ust_fls(count
) - 1;
678 if (count
& (count
- 1))
683 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */