2 * ring_buffer_frontend.c
4 * (C) Copyright 2005-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 * Ring buffer wait-free buffer synchronization. Producer-consumer and flight
7 * recorder (overwrite) modes. See thesis:
9 * Desnoyers, Mathieu (2009), "Low-Impact Operating System Tracing", Ph.D.
10 * dissertation, Ecole Polytechnique de Montreal.
11 * http://www.lttng.org/pub/thesis/desnoyers-dissertation-2009-12.pdf
13 * - Algorithm presentation in Chapter 5:
14 * "Lockless Multi-Core High-Throughput Buffering".
15 * - Algorithm formal verification in Section 8.6:
16 * "Formal verification of LTTng"
19 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
21 * Inspired from LTT and RelayFS:
22 * Karim Yaghmour <karim@opersys.com>
23 * Tom Zanussi <zanussi@us.ibm.com>
24 * Bob Wisniewski <bob@watson.ibm.com>
26 * Bob Wisniewski <bob@watson.ibm.com>
28 * Buffer reader semantic :
31 * while buffer is not finalized and empty
33 * - if return value != 0, continue
34 * - splice one subbuffer worth of data to a pipe
35 * - splice the data from pipe to disk/network
38 * Dual LGPL v2.1/GPL v2 license.
41 #include <sys/types.h>
45 #include <urcu/compiler.h>
50 #include <lttng/ringbuffer-config.h>
57 #define max(a, b) ((a) > (b) ? (a) : (b))
61 * Use POSIX SHM: shm_open(3) and shm_unlink(3).
62 * close(2) to close the fd returned by shm_open.
63 * shm_unlink releases the shared memory object name.
64 * ftruncate(2) sets the size of the memory object.
65 * mmap/munmap maps the shared memory obj to a virtual address in the
66 * calling proceess (should be done both in libust and consumer).
67 * See shm_overview(7) for details.
68 * Pass file descriptor returned by shm_open(3) to ltt-sessiond through
71 * Since we don't need to access the object using its name, we can
72 * immediately shm_unlink(3) it, and only keep the handle with its file
77 * Internal structure representing offsets to use at a sub-buffer switch.
79 struct switch_offsets
{
80 unsigned long begin
, end
, old
;
81 size_t pre_header_padding
, size
;
82 unsigned int switch_new_start
:1, switch_new_end
:1, switch_old_start
:1,
86 __thread
unsigned int lib_ring_buffer_nesting
;
89 * TODO: this is unused. Errors are saved within the ring buffer.
90 * Eventually, allow consumerd to print these errors.
93 void lib_ring_buffer_print_errors(struct channel
*chan
,
94 struct lttng_ust_lib_ring_buffer
*buf
, int cpu
,
95 struct lttng_ust_shm_handle
*handle
);
98 * lib_ring_buffer_reset - Reset ring buffer to initial values.
101 * Effectively empty the ring buffer. Should be called when the buffer is not
102 * used for writing. The ring buffer can be opened for reading, but the reader
103 * should not be using the iterator concurrently with reset. The previous
104 * current iterator record is reset.
106 void lib_ring_buffer_reset(struct lttng_ust_lib_ring_buffer
*buf
,
107 struct lttng_ust_shm_handle
*handle
)
109 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
110 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
114 * Reset iterator first. It will put the subbuffer if it currently holds
117 v_set(config
, &buf
->offset
, 0);
118 for (i
= 0; i
< chan
->backend
.num_subbuf
; i
++) {
119 v_set(config
, &shmp_index(handle
, buf
->commit_hot
, i
)->cc
, 0);
120 v_set(config
, &shmp_index(handle
, buf
->commit_hot
, i
)->seq
, 0);
121 v_set(config
, &shmp_index(handle
, buf
->commit_cold
, i
)->cc_sb
, 0);
123 uatomic_set(&buf
->consumed
, 0);
124 uatomic_set(&buf
->record_disabled
, 0);
125 v_set(config
, &buf
->last_tsc
, 0);
126 lib_ring_buffer_backend_reset(&buf
->backend
, handle
);
127 /* Don't reset number of active readers */
128 v_set(config
, &buf
->records_lost_full
, 0);
129 v_set(config
, &buf
->records_lost_wrap
, 0);
130 v_set(config
, &buf
->records_lost_big
, 0);
131 v_set(config
, &buf
->records_count
, 0);
132 v_set(config
, &buf
->records_overrun
, 0);
137 * channel_reset - Reset channel to initial values.
140 * Effectively empty the channel. Should be called when the channel is not used
141 * for writing. The channel can be opened for reading, but the reader should not
142 * be using the iterator concurrently with reset. The previous current iterator
145 void channel_reset(struct channel
*chan
)
148 * Reset iterators first. Will put the subbuffer if held for reading.
150 uatomic_set(&chan
->record_disabled
, 0);
151 /* Don't reset commit_count_mask, still valid */
152 channel_backend_reset(&chan
->backend
);
153 /* Don't reset switch/read timer interval */
154 /* Don't reset notifiers and notifier enable bits */
155 /* Don't reset reader reference count */
159 * Must be called under cpu hotplug protection.
161 int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer
*buf
,
162 struct channel_backend
*chanb
, int cpu
,
163 struct lttng_ust_shm_handle
*handle
,
164 struct shm_object
*shmobj
)
166 const struct lttng_ust_lib_ring_buffer_config
*config
= &chanb
->config
;
167 struct channel
*chan
= caa_container_of(chanb
, struct channel
, backend
);
168 void *priv
= channel_get_private(chan
);
169 size_t subbuf_header_size
;
173 /* Test for cpu hotplug */
174 if (buf
->backend
.allocated
)
177 ret
= lib_ring_buffer_backend_create(&buf
->backend
, &chan
->backend
,
178 cpu
, handle
, shmobj
);
182 align_shm(shmobj
, __alignof__(struct commit_counters_hot
));
183 set_shmp(buf
->commit_hot
,
185 sizeof(struct commit_counters_hot
) * chan
->backend
.num_subbuf
));
186 if (!shmp(handle
, buf
->commit_hot
)) {
191 align_shm(shmobj
, __alignof__(struct commit_counters_cold
));
192 set_shmp(buf
->commit_cold
,
194 sizeof(struct commit_counters_cold
) * chan
->backend
.num_subbuf
));
195 if (!shmp(handle
, buf
->commit_cold
)) {
201 * Write the subbuffer header for first subbuffer so we know the total
202 * duration of data gathering.
204 subbuf_header_size
= config
->cb
.subbuffer_header_size();
205 v_set(config
, &buf
->offset
, subbuf_header_size
);
206 subbuffer_id_clear_noref(config
, &shmp_index(handle
, buf
->backend
.buf_wsb
, 0)->id
);
207 tsc
= config
->cb
.ring_buffer_clock_read(shmp(handle
, buf
->backend
.chan
));
208 config
->cb
.buffer_begin(buf
, tsc
, 0, handle
);
209 v_add(config
, subbuf_header_size
, &shmp_index(handle
, buf
->commit_hot
, 0)->cc
);
211 if (config
->cb
.buffer_create
) {
212 ret
= config
->cb
.buffer_create(buf
, priv
, cpu
, chanb
->name
, handle
);
216 buf
->backend
.allocated
= 1;
221 /* commit_cold will be freed by shm teardown */
223 /* commit_hot will be freed by shm teardown */
229 static void switch_buffer_timer(unsigned long data
)
231 struct lttng_ust_lib_ring_buffer
*buf
= (struct lttng_ust_lib_ring_buffer
*)data
;
232 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
233 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
236 * Only flush buffers periodically if readers are active.
238 if (uatomic_read(&buf
->active_readers
) || uatomic_read(&buf
->active_shadow_readers
))
239 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
, handle
);
242 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
243 // mod_timer_pinned(&buf->switch_timer,
244 // jiffies + chan->switch_timer_interval);
246 // mod_timer(&buf->switch_timer,
247 // jiffies + chan->switch_timer_interval);
251 static void lib_ring_buffer_start_switch_timer(struct lttng_ust_lib_ring_buffer
*buf
,
252 struct lttng_ust_shm_handle
*handle
)
254 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
255 //const struct lttng_ust_lib_ring_buffer_config *config = &chan->backend.config;
257 if (!chan
->switch_timer_interval
|| buf
->switch_timer_enabled
)
260 //init_timer(&buf->switch_timer);
261 //buf->switch_timer.function = switch_buffer_timer;
262 //buf->switch_timer.expires = jiffies + chan->switch_timer_interval;
263 //buf->switch_timer.data = (unsigned long)buf;
264 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
265 // add_timer_on(&buf->switch_timer, buf->backend.cpu);
267 // add_timer(&buf->switch_timer);
268 buf
->switch_timer_enabled
= 1;
271 static void lib_ring_buffer_stop_switch_timer(struct lttng_ust_lib_ring_buffer
*buf
,
272 struct lttng_ust_shm_handle
*handle
)
274 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
276 if (!chan
->switch_timer_interval
|| !buf
->switch_timer_enabled
)
280 //del_timer_sync(&buf->switch_timer);
281 buf
->switch_timer_enabled
= 0;
286 * Polling timer to check the channels for data.
288 static void read_buffer_timer(unsigned long data
)
290 struct lttng_ust_lib_ring_buffer
*buf
= (struct lttng_ust_lib_ring_buffer
*)data
;
291 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
292 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
294 CHAN_WARN_ON(chan
, !buf
->backend
.allocated
);
296 if (uatomic_read(&buf
->active_readers
) || uatomic_read(&buf
->active_shadow_readers
))
297 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
299 //wake_up_interruptible(&buf->read_wait);
300 //wake_up_interruptible(&chan->read_wait);
304 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
305 // mod_timer_pinned(&buf->read_timer,
306 // jiffies + chan->read_timer_interval);
308 // mod_timer(&buf->read_timer,
309 // jiffies + chan->read_timer_interval);
313 static void lib_ring_buffer_start_read_timer(struct lttng_ust_lib_ring_buffer
*buf
,
314 struct lttng_ust_shm_handle
*handle
)
316 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
317 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
319 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
320 || !chan
->read_timer_interval
321 || buf
->read_timer_enabled
)
325 //init_timer(&buf->read_timer);
326 //buf->read_timer.function = read_buffer_timer;
327 //buf->read_timer.expires = jiffies + chan->read_timer_interval;
328 //buf->read_timer.data = (unsigned long)buf;
330 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
331 // add_timer_on(&buf->read_timer, buf->backend.cpu);
333 // add_timer(&buf->read_timer);
334 buf
->read_timer_enabled
= 1;
337 static void lib_ring_buffer_stop_read_timer(struct lttng_ust_lib_ring_buffer
*buf
,
338 struct lttng_ust_shm_handle
*handle
)
340 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
341 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
343 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
344 || !chan
->read_timer_interval
345 || !buf
->read_timer_enabled
)
349 //del_timer_sync(&buf->read_timer);
351 * do one more check to catch data that has been written in the last
354 if (lib_ring_buffer_poll_deliver(config
, buf
, chan
, handle
)) {
356 //wake_up_interruptible(&buf->read_wait);
357 //wake_up_interruptible(&chan->read_wait);
359 buf
->read_timer_enabled
= 0;
362 static void channel_unregister_notifiers(struct channel
*chan
,
363 struct lttng_ust_shm_handle
*handle
)
365 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
368 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
369 for_each_possible_cpu(cpu
) {
370 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
372 lib_ring_buffer_stop_switch_timer(buf
, handle
);
373 lib_ring_buffer_stop_read_timer(buf
, handle
);
376 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[0].shmp
);
378 lib_ring_buffer_stop_switch_timer(buf
, handle
);
379 lib_ring_buffer_stop_read_timer(buf
, handle
);
381 //channel_backend_unregister_notifiers(&chan->backend);
384 static void channel_free(struct channel
*chan
, struct lttng_ust_shm_handle
*handle
,
388 channel_backend_free(&chan
->backend
, handle
);
389 /* chan is freed by shm teardown */
390 shm_object_table_destroy(handle
->table
);
395 * channel_create - Create channel.
396 * @config: ring buffer instance configuration
397 * @name: name of the channel
398 * @priv_data: ring buffer client private data area pointer (output)
399 * @priv_data_size: length, in bytes, of the private data area.
400 * @priv_data_init: initialization data for private data.
401 * @buf_addr: pointer the the beginning of the preallocated buffer contiguous
402 * address mapping. It is used only by RING_BUFFER_STATIC
403 * configuration. It can be set to NULL for other backends.
404 * @subbuf_size: subbuffer size
405 * @num_subbuf: number of subbuffers
406 * @switch_timer_interval: Time interval (in us) to fill sub-buffers with
407 * padding to let readers get those sub-buffers.
408 * Used for live streaming.
409 * @read_timer_interval: Time interval (in us) to wake up pending readers.
412 * Returns NULL on failure.
414 struct lttng_ust_shm_handle
*channel_create(const struct lttng_ust_lib_ring_buffer_config
*config
,
417 size_t priv_data_align
,
418 size_t priv_data_size
,
419 void *priv_data_init
,
420 void *buf_addr
, size_t subbuf_size
,
421 size_t num_subbuf
, unsigned int switch_timer_interval
,
422 unsigned int read_timer_interval
,
423 int **shm_fd
, int **wait_fd
, uint64_t **memory_map_size
)
426 size_t shmsize
, chansize
;
427 struct channel
*chan
;
428 struct lttng_ust_shm_handle
*handle
;
429 struct shm_object
*shmobj
;
432 if (lib_ring_buffer_check_config(config
, switch_timer_interval
,
433 read_timer_interval
))
436 handle
= zmalloc(sizeof(struct lttng_ust_shm_handle
));
440 /* Allocate table for channel + per-cpu buffers */
441 handle
->table
= shm_object_table_create(1 + num_possible_cpus());
443 goto error_table_alloc
;
445 /* Calculate the shm allocation layout */
446 shmsize
= sizeof(struct channel
);
447 shmsize
+= offset_align(shmsize
, __alignof__(struct lttng_ust_lib_ring_buffer_shmp
));
448 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
449 shmsize
+= sizeof(struct lttng_ust_lib_ring_buffer_shmp
) * num_possible_cpus();
451 shmsize
+= sizeof(struct lttng_ust_lib_ring_buffer_shmp
);
453 shmsize
+= offset_align(shmsize
, priv_data_align
);
454 shmsize
+= priv_data_size
;
456 shmobj
= shm_object_table_append(handle
->table
, shmsize
);
459 /* struct channel is at object 0, offset 0 (hardcoded) */
460 set_shmp(handle
->chan
, zalloc_shm(shmobj
, chansize
));
461 assert(handle
->chan
._ref
.index
== 0);
462 assert(handle
->chan
._ref
.offset
== 0);
463 chan
= shmp(handle
, handle
->chan
);
467 /* space for private data */
468 if (priv_data_size
) {
469 DECLARE_SHMP(void, priv_data_alloc
);
471 align_shm(shmobj
, priv_data_align
);
472 chan
->priv_data_offset
= shmobj
->allocated_len
;
473 set_shmp(priv_data_alloc
, zalloc_shm(shmobj
, priv_data_size
));
474 if (!shmp(handle
, priv_data_alloc
))
476 *priv_data
= channel_get_private(chan
);
477 memcpy(*priv_data
, priv_data_init
, priv_data_size
);
479 chan
->priv_data_offset
= -1;
483 ret
= channel_backend_init(&chan
->backend
, name
, config
,
484 subbuf_size
, num_subbuf
, handle
);
486 goto error_backend_init
;
488 chan
->commit_count_mask
= (~0UL >> chan
->backend
.num_subbuf_order
);
490 //chan->switch_timer_interval = usecs_to_jiffies(switch_timer_interval);
491 //chan->read_timer_interval = usecs_to_jiffies(read_timer_interval);
493 //init_waitqueue_head(&chan->read_wait);
494 //init_waitqueue_head(&chan->hp_wait);
496 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
498 * In case of non-hotplug cpu, if the ring-buffer is allocated
499 * in early initcall, it will not be notified of secondary cpus.
500 * In that off case, we need to allocate for all possible cpus.
502 for_each_possible_cpu(cpu
) {
503 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
504 lib_ring_buffer_start_switch_timer(buf
, handle
);
505 lib_ring_buffer_start_read_timer(buf
, handle
);
508 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[0].shmp
);
510 lib_ring_buffer_start_switch_timer(buf
, handle
);
511 lib_ring_buffer_start_read_timer(buf
, handle
);
513 ref
= &handle
->chan
._ref
;
514 shm_get_object_data(handle
, ref
, shm_fd
, wait_fd
, memory_map_size
);
519 shm_object_table_destroy(handle
->table
);
525 struct lttng_ust_shm_handle
*channel_handle_create(int shm_fd
, int wait_fd
,
526 uint64_t memory_map_size
)
528 struct lttng_ust_shm_handle
*handle
;
529 struct shm_object
*object
;
531 handle
= zmalloc(sizeof(struct lttng_ust_shm_handle
));
535 /* Allocate table for channel + per-cpu buffers */
536 handle
->table
= shm_object_table_create(1 + num_possible_cpus());
538 goto error_table_alloc
;
539 /* Add channel object */
540 object
= shm_object_table_append_shadow(handle
->table
,
541 shm_fd
, wait_fd
, memory_map_size
);
543 goto error_table_object
;
544 /* struct channel is at object 0, offset 0 (hardcoded) */
545 handle
->chan
._ref
.index
= 0;
546 handle
->chan
._ref
.offset
= 0;
550 shm_object_table_destroy(handle
->table
);
556 int channel_handle_add_stream(struct lttng_ust_shm_handle
*handle
,
557 int shm_fd
, int wait_fd
, uint64_t memory_map_size
)
559 struct shm_object
*object
;
561 /* Add stream object */
562 object
= shm_object_table_append_shadow(handle
->table
,
563 shm_fd
, wait_fd
, memory_map_size
);
570 void channel_release(struct channel
*chan
, struct lttng_ust_shm_handle
*handle
,
573 channel_free(chan
, handle
, shadow
);
577 * channel_destroy - Finalize, wait for q.s. and destroy channel.
578 * @chan: channel to destroy
581 * Call "destroy" callback, finalize channels, decrement the channel
582 * reference count. Note that when readers have completed data
583 * consumption of finalized channels, get_subbuf() will return -ENODATA.
584 * They should release their handle at that point.
586 void channel_destroy(struct channel
*chan
, struct lttng_ust_shm_handle
*handle
,
590 channel_release(chan
, handle
, shadow
);
594 channel_unregister_notifiers(chan
, handle
);
597 * Note: the consumer takes care of finalizing and switching the
602 * sessiond/consumer are keeping a reference on the shm file
603 * descriptor directly. No need to refcount.
605 channel_release(chan
, handle
, shadow
);
609 struct lttng_ust_lib_ring_buffer
*channel_get_ring_buffer(
610 const struct lttng_ust_lib_ring_buffer_config
*config
,
611 struct channel
*chan
, int cpu
,
612 struct lttng_ust_shm_handle
*handle
,
613 int **shm_fd
, int **wait_fd
,
614 uint64_t **memory_map_size
)
618 if (config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
) {
619 ref
= &chan
->backend
.buf
[0].shmp
._ref
;
620 shm_get_object_data(handle
, ref
, shm_fd
, wait_fd
,
622 return shmp(handle
, chan
->backend
.buf
[0].shmp
);
624 if (cpu
>= num_possible_cpus())
626 ref
= &chan
->backend
.buf
[cpu
].shmp
._ref
;
627 shm_get_object_data(handle
, ref
, shm_fd
, wait_fd
,
629 return shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
633 int lib_ring_buffer_open_read(struct lttng_ust_lib_ring_buffer
*buf
,
634 struct lttng_ust_shm_handle
*handle
,
638 if (uatomic_cmpxchg(&buf
->active_shadow_readers
, 0, 1) != 0)
643 if (uatomic_cmpxchg(&buf
->active_readers
, 0, 1) != 0)
649 void lib_ring_buffer_release_read(struct lttng_ust_lib_ring_buffer
*buf
,
650 struct lttng_ust_shm_handle
*handle
,
653 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
656 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_shadow_readers
) != 1);
658 uatomic_dec(&buf
->active_shadow_readers
);
661 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_readers
) != 1);
663 uatomic_dec(&buf
->active_readers
);
667 * lib_ring_buffer_snapshot - save subbuffer position snapshot (for read)
669 * @consumed: consumed count indicating the position where to read
670 * @produced: produced count, indicates position when to stop reading
672 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
673 * data to read at consumed position, or 0 if the get operation succeeds.
676 int lib_ring_buffer_snapshot(struct lttng_ust_lib_ring_buffer
*buf
,
677 unsigned long *consumed
, unsigned long *produced
,
678 struct lttng_ust_shm_handle
*handle
)
680 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
681 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
682 unsigned long consumed_cur
, write_offset
;
685 finalized
= CMM_ACCESS_ONCE(buf
->finalized
);
687 * Read finalized before counters.
690 consumed_cur
= uatomic_read(&buf
->consumed
);
692 * No need to issue a memory barrier between consumed count read and
693 * write offset read, because consumed count can only change
694 * concurrently in overwrite mode, and we keep a sequence counter
695 * identifier derived from the write offset to check we are getting
696 * the same sub-buffer we are expecting (the sub-buffers are atomically
697 * "tagged" upon writes, tags are checked upon read).
699 write_offset
= v_read(config
, &buf
->offset
);
702 * Check that we are not about to read the same subbuffer in
703 * which the writer head is.
705 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_cur
, chan
)
709 *consumed
= consumed_cur
;
710 *produced
= subbuf_trunc(write_offset
, chan
);
716 * The memory barriers __wait_event()/wake_up_interruptible() take care
717 * of "raw_spin_is_locked" memory ordering.
726 * lib_ring_buffer_put_snapshot - move consumed counter forward
728 * @consumed_new: new consumed count value
730 void lib_ring_buffer_move_consumer(struct lttng_ust_lib_ring_buffer
*buf
,
731 unsigned long consumed_new
,
732 struct lttng_ust_shm_handle
*handle
)
734 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &buf
->backend
;
735 struct channel
*chan
= shmp(handle
, bufb
->chan
);
736 unsigned long consumed
;
738 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_readers
) != 1
739 && uatomic_read(&buf
->active_shadow_readers
) != 1);
742 * Only push the consumed value forward.
743 * If the consumed cmpxchg fails, this is because we have been pushed by
744 * the writer in flight recorder mode.
746 consumed
= uatomic_read(&buf
->consumed
);
747 while ((long) consumed
- (long) consumed_new
< 0)
748 consumed
= uatomic_cmpxchg(&buf
->consumed
, consumed
,
753 * lib_ring_buffer_get_subbuf - get exclusive access to subbuffer for reading
755 * @consumed: consumed count indicating the position where to read
757 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
758 * data to read at consumed position, or 0 if the get operation succeeds.
760 int lib_ring_buffer_get_subbuf(struct lttng_ust_lib_ring_buffer
*buf
,
761 unsigned long consumed
,
762 struct lttng_ust_shm_handle
*handle
)
764 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
765 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
766 unsigned long consumed_cur
, consumed_idx
, commit_count
, write_offset
;
771 finalized
= CMM_ACCESS_ONCE(buf
->finalized
);
773 * Read finalized before counters.
776 consumed_cur
= uatomic_read(&buf
->consumed
);
777 consumed_idx
= subbuf_index(consumed
, chan
);
778 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_cold
, consumed_idx
)->cc_sb
);
780 * Make sure we read the commit count before reading the buffer
781 * data and the write offset. Correct consumed offset ordering
782 * wrt commit count is insured by the use of cmpxchg to update
783 * the consumed offset.
786 * Local rmb to match the remote wmb to read the commit count
787 * before the buffer data and the write offset.
791 write_offset
= v_read(config
, &buf
->offset
);
794 * Check that the buffer we are getting is after or at consumed_cur
797 if ((long) subbuf_trunc(consumed
, chan
)
798 - (long) subbuf_trunc(consumed_cur
, chan
) < 0)
802 * Check that the subbuffer we are trying to consume has been
803 * already fully committed.
805 if (((commit_count
- chan
->backend
.subbuf_size
)
806 & chan
->commit_count_mask
)
807 - (buf_trunc(consumed_cur
, chan
)
808 >> chan
->backend
.num_subbuf_order
)
813 * Check that we are not about to read the same subbuffer in
814 * which the writer head is.
816 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_cur
, chan
)
821 * Failure to get the subbuffer causes a busy-loop retry without going
822 * to a wait queue. These are caused by short-lived race windows where
823 * the writer is getting access to a subbuffer we were trying to get
824 * access to. Also checks that the "consumed" buffer count we are
825 * looking for matches the one contained in the subbuffer id.
827 ret
= update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
828 consumed_idx
, buf_trunc_val(consumed
, chan
),
832 subbuffer_id_clear_noref(config
, &buf
->backend
.buf_rsb
.id
);
834 buf
->get_subbuf_consumed
= consumed
;
841 * The memory barriers __wait_event()/wake_up_interruptible() take care
842 * of "raw_spin_is_locked" memory ordering.
851 * lib_ring_buffer_put_subbuf - release exclusive subbuffer access
854 void lib_ring_buffer_put_subbuf(struct lttng_ust_lib_ring_buffer
*buf
,
855 struct lttng_ust_shm_handle
*handle
)
857 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &buf
->backend
;
858 struct channel
*chan
= shmp(handle
, bufb
->chan
);
859 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
860 unsigned long read_sb_bindex
, consumed_idx
, consumed
;
862 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_readers
) != 1
863 && uatomic_read(&buf
->active_shadow_readers
) != 1);
865 if (!buf
->get_subbuf
) {
867 * Reader puts a subbuffer it did not get.
869 CHAN_WARN_ON(chan
, 1);
872 consumed
= buf
->get_subbuf_consumed
;
876 * Clear the records_unread counter. (overruns counter)
877 * Can still be non-zero if a file reader simply grabbed the data
878 * without using iterators.
879 * Can be below zero if an iterator is used on a snapshot more than
882 read_sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
883 v_add(config
, v_read(config
,
884 &shmp(handle
, shmp_index(handle
, bufb
->array
, read_sb_bindex
)->shmp
)->records_unread
),
885 &bufb
->records_read
);
886 v_set(config
, &shmp(handle
, shmp_index(handle
, bufb
->array
, read_sb_bindex
)->shmp
)->records_unread
, 0);
887 CHAN_WARN_ON(chan
, config
->mode
== RING_BUFFER_OVERWRITE
888 && subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
889 subbuffer_id_set_noref(config
, &bufb
->buf_rsb
.id
);
892 * Exchange the reader subbuffer with the one we put in its place in the
893 * writer subbuffer table. Expect the original consumed count. If
894 * update_read_sb_index fails, this is because the writer updated the
895 * subbuffer concurrently. We should therefore keep the subbuffer we
896 * currently have: it has become invalid to try reading this sub-buffer
897 * consumed count value anyway.
899 consumed_idx
= subbuf_index(consumed
, chan
);
900 update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
901 consumed_idx
, buf_trunc_val(consumed
, chan
),
904 * update_read_sb_index return value ignored. Don't exchange sub-buffer
905 * if the writer concurrently updated it.
910 * cons_offset is an iterator on all subbuffer offsets between the reader
911 * position and the writer position. (inclusive)
914 void lib_ring_buffer_print_subbuffer_errors(struct lttng_ust_lib_ring_buffer
*buf
,
915 struct channel
*chan
,
916 unsigned long cons_offset
,
918 struct lttng_ust_shm_handle
*handle
)
920 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
921 unsigned long cons_idx
, commit_count
, commit_count_sb
;
923 cons_idx
= subbuf_index(cons_offset
, chan
);
924 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, cons_idx
)->cc
);
925 commit_count_sb
= v_read(config
, &shmp_index(handle
, buf
->commit_cold
, cons_idx
)->cc_sb
);
927 if (subbuf_offset(commit_count
, chan
) != 0)
928 DBG("ring buffer %s, cpu %d: "
929 "commit count in subbuffer %lu,\n"
930 "expecting multiples of %lu bytes\n"
931 " [ %lu bytes committed, %lu bytes reader-visible ]\n",
932 chan
->backend
.name
, cpu
, cons_idx
,
933 chan
->backend
.subbuf_size
,
934 commit_count
, commit_count_sb
);
936 DBG("ring buffer: %s, cpu %d: %lu bytes committed\n",
937 chan
->backend
.name
, cpu
, commit_count
);
941 void lib_ring_buffer_print_buffer_errors(struct lttng_ust_lib_ring_buffer
*buf
,
942 struct channel
*chan
,
944 struct lttng_ust_shm_handle
*handle
)
946 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
947 unsigned long write_offset
, cons_offset
;
950 * No need to order commit_count, write_offset and cons_offset reads
951 * because we execute at teardown when no more writer nor reader
952 * references are left.
954 write_offset
= v_read(config
, &buf
->offset
);
955 cons_offset
= uatomic_read(&buf
->consumed
);
956 if (write_offset
!= cons_offset
)
957 DBG("ring buffer %s, cpu %d: "
958 "non-consumed data\n"
959 " [ %lu bytes written, %lu bytes read ]\n",
960 chan
->backend
.name
, cpu
, write_offset
, cons_offset
);
962 for (cons_offset
= uatomic_read(&buf
->consumed
);
963 (long) (subbuf_trunc((unsigned long) v_read(config
, &buf
->offset
),
966 cons_offset
= subbuf_align(cons_offset
, chan
))
967 lib_ring_buffer_print_subbuffer_errors(buf
, chan
, cons_offset
,
972 void lib_ring_buffer_print_errors(struct channel
*chan
,
973 struct lttng_ust_lib_ring_buffer
*buf
, int cpu
,
974 struct lttng_ust_shm_handle
*handle
)
976 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
977 void *priv
= channel_get_private(chan
);
979 DBG("ring buffer %s, cpu %d: %lu records written, "
980 "%lu records overrun\n",
981 chan
->backend
.name
, cpu
,
982 v_read(config
, &buf
->records_count
),
983 v_read(config
, &buf
->records_overrun
));
985 if (v_read(config
, &buf
->records_lost_full
)
986 || v_read(config
, &buf
->records_lost_wrap
)
987 || v_read(config
, &buf
->records_lost_big
))
988 DBG("ring buffer %s, cpu %d: records were lost. Caused by:\n"
989 " [ %lu buffer full, %lu nest buffer wrap-around, "
990 "%lu event too big ]\n",
991 chan
->backend
.name
, cpu
,
992 v_read(config
, &buf
->records_lost_full
),
993 v_read(config
, &buf
->records_lost_wrap
),
994 v_read(config
, &buf
->records_lost_big
));
996 lib_ring_buffer_print_buffer_errors(buf
, chan
, priv
, cpu
, handle
);
1000 * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
1002 * Only executed when the buffer is finalized, in SWITCH_FLUSH.
1005 void lib_ring_buffer_switch_old_start(struct lttng_ust_lib_ring_buffer
*buf
,
1006 struct channel
*chan
,
1007 struct switch_offsets
*offsets
,
1009 struct lttng_ust_shm_handle
*handle
)
1011 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1012 unsigned long oldidx
= subbuf_index(offsets
->old
, chan
);
1013 unsigned long commit_count
;
1015 config
->cb
.buffer_begin(buf
, tsc
, oldidx
, handle
);
1018 * Order all writes to buffer before the commit count update that will
1019 * determine that the subbuffer is full.
1022 v_add(config
, config
->cb
.subbuffer_header_size(),
1023 &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1024 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1025 /* Check if the written buffer has to be delivered */
1026 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
,
1027 commit_count
, oldidx
, handle
);
1028 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, oldidx
,
1029 offsets
->old
, commit_count
,
1030 config
->cb
.subbuffer_header_size(),
1035 * lib_ring_buffer_switch_old_end: switch old subbuffer
1037 * Note : offset_old should never be 0 here. It is ok, because we never perform
1038 * buffer switch on an empty subbuffer in SWITCH_ACTIVE mode. The caller
1039 * increments the offset_old value when doing a SWITCH_FLUSH on an empty
1043 void lib_ring_buffer_switch_old_end(struct lttng_ust_lib_ring_buffer
*buf
,
1044 struct channel
*chan
,
1045 struct switch_offsets
*offsets
,
1047 struct lttng_ust_shm_handle
*handle
)
1049 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1050 unsigned long oldidx
= subbuf_index(offsets
->old
- 1, chan
);
1051 unsigned long commit_count
, padding_size
, data_size
;
1053 data_size
= subbuf_offset(offsets
->old
- 1, chan
) + 1;
1054 padding_size
= chan
->backend
.subbuf_size
- data_size
;
1055 subbuffer_set_data_size(config
, &buf
->backend
, oldidx
, data_size
,
1059 * Order all writes to buffer before the commit count update that will
1060 * determine that the subbuffer is full.
1063 v_add(config
, padding_size
, &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1064 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1065 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
- 1,
1066 commit_count
, oldidx
, handle
);
1067 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, oldidx
,
1068 offsets
->old
, commit_count
,
1069 padding_size
, handle
);
1073 * lib_ring_buffer_switch_new_start: Populate new subbuffer.
1075 * This code can be executed unordered : writers may already have written to the
1076 * sub-buffer before this code gets executed, caution. The commit makes sure
1077 * that this code is executed before the deliver of this sub-buffer.
1080 void lib_ring_buffer_switch_new_start(struct lttng_ust_lib_ring_buffer
*buf
,
1081 struct channel
*chan
,
1082 struct switch_offsets
*offsets
,
1084 struct lttng_ust_shm_handle
*handle
)
1086 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1087 unsigned long beginidx
= subbuf_index(offsets
->begin
, chan
);
1088 unsigned long commit_count
;
1090 config
->cb
.buffer_begin(buf
, tsc
, beginidx
, handle
);
1093 * Order all writes to buffer before the commit count update that will
1094 * determine that the subbuffer is full.
1097 v_add(config
, config
->cb
.subbuffer_header_size(),
1098 &shmp_index(handle
, buf
->commit_hot
, beginidx
)->cc
);
1099 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, beginidx
)->cc
);
1100 /* Check if the written buffer has to be delivered */
1101 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->begin
,
1102 commit_count
, beginidx
, handle
);
1103 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, beginidx
,
1104 offsets
->begin
, commit_count
,
1105 config
->cb
.subbuffer_header_size(),
1110 * lib_ring_buffer_switch_new_end: finish switching current subbuffer
1112 * The only remaining threads could be the ones with pending commits. They will
1113 * have to do the deliver themselves.
1116 void lib_ring_buffer_switch_new_end(struct lttng_ust_lib_ring_buffer
*buf
,
1117 struct channel
*chan
,
1118 struct switch_offsets
*offsets
,
1120 struct lttng_ust_shm_handle
*handle
)
1122 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1123 unsigned long endidx
= subbuf_index(offsets
->end
- 1, chan
);
1124 unsigned long commit_count
, padding_size
, data_size
;
1126 data_size
= subbuf_offset(offsets
->end
- 1, chan
) + 1;
1127 padding_size
= chan
->backend
.subbuf_size
- data_size
;
1128 subbuffer_set_data_size(config
, &buf
->backend
, endidx
, data_size
,
1132 * Order all writes to buffer before the commit count update that will
1133 * determine that the subbuffer is full.
1136 v_add(config
, padding_size
, &shmp_index(handle
, buf
->commit_hot
, endidx
)->cc
);
1137 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, endidx
)->cc
);
1138 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->end
- 1,
1139 commit_count
, endidx
, handle
);
1140 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, endidx
,
1141 offsets
->end
, commit_count
,
1142 padding_size
, handle
);
1148 * !0 if execution must be aborted.
1151 int lib_ring_buffer_try_switch_slow(enum switch_mode mode
,
1152 struct lttng_ust_lib_ring_buffer
*buf
,
1153 struct channel
*chan
,
1154 struct switch_offsets
*offsets
,
1157 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1160 offsets
->begin
= v_read(config
, &buf
->offset
);
1161 offsets
->old
= offsets
->begin
;
1162 offsets
->switch_old_start
= 0;
1163 off
= subbuf_offset(offsets
->begin
, chan
);
1165 *tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1168 * Ensure we flush the header of an empty subbuffer when doing the
1169 * finalize (SWITCH_FLUSH). This ensures that we end up knowing the
1170 * total data gathering duration even if there were no records saved
1171 * after the last buffer switch.
1172 * In SWITCH_ACTIVE mode, switch the buffer when it contains events.
1173 * SWITCH_ACTIVE only flushes the current subbuffer, dealing with end of
1174 * subbuffer header as appropriate.
1175 * The next record that reserves space will be responsible for
1176 * populating the following subbuffer header. We choose not to populate
1177 * the next subbuffer header here because we want to be able to use
1178 * SWITCH_ACTIVE for periodical buffer flush, which must
1179 * guarantee that all the buffer content (records and header
1180 * timestamps) are visible to the reader. This is required for
1181 * quiescence guarantees for the fusion merge.
1183 if (mode
== SWITCH_FLUSH
|| off
> 0) {
1184 if (caa_unlikely(off
== 0)) {
1186 * The client does not save any header information.
1187 * Don't switch empty subbuffer on finalize, because it
1188 * is invalid to deliver a completely empty subbuffer.
1190 if (!config
->cb
.subbuffer_header_size())
1193 * Need to write the subbuffer start header on finalize.
1195 offsets
->switch_old_start
= 1;
1197 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1199 return -1; /* we do not have to switch : buffer is empty */
1200 /* Note: old points to the next subbuf at offset 0 */
1201 offsets
->end
= offsets
->begin
;
1206 * Force a sub-buffer switch. This operation is completely reentrant : can be
1207 * called while tracing is active with absolutely no lock held.
1209 * Note, however, that as a v_cmpxchg is used for some atomic
1210 * operations, this function must be called from the CPU which owns the buffer
1211 * for a ACTIVE flush.
1213 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer
*buf
, enum switch_mode mode
,
1214 struct lttng_ust_shm_handle
*handle
)
1216 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
1217 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1218 struct switch_offsets offsets
;
1219 unsigned long oldidx
;
1225 * Perform retryable operations.
1228 if (lib_ring_buffer_try_switch_slow(mode
, buf
, chan
, &offsets
,
1230 return; /* Switch not needed */
1231 } while (v_cmpxchg(config
, &buf
->offset
, offsets
.old
, offsets
.end
)
1235 * Atomically update last_tsc. This update races against concurrent
1236 * atomic updates, but the race will always cause supplementary full TSC
1237 * records, never the opposite (missing a full TSC record when it would
1240 save_last_tsc(config
, buf
, tsc
);
1243 * Push the reader if necessary
1245 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.old
);
1247 oldidx
= subbuf_index(offsets
.old
, chan
);
1248 lib_ring_buffer_clear_noref(config
, &buf
->backend
, oldidx
, handle
);
1251 * May need to populate header start on SWITCH_FLUSH.
1253 if (offsets
.switch_old_start
) {
1254 lib_ring_buffer_switch_old_start(buf
, chan
, &offsets
, tsc
, handle
);
1255 offsets
.old
+= config
->cb
.subbuffer_header_size();
1259 * Switch old subbuffer.
1261 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, tsc
, handle
);
1267 * -ENOSPC if event size is too large for packet.
1268 * -ENOBUFS if there is currently not enough space in buffer for the event.
1269 * -EIO if data cannot be written into the buffer for any other reason.
1272 int lib_ring_buffer_try_reserve_slow(struct lttng_ust_lib_ring_buffer
*buf
,
1273 struct channel
*chan
,
1274 struct switch_offsets
*offsets
,
1275 struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
1277 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1278 struct lttng_ust_shm_handle
*handle
= ctx
->handle
;
1279 unsigned long reserve_commit_diff
;
1281 offsets
->begin
= v_read(config
, &buf
->offset
);
1282 offsets
->old
= offsets
->begin
;
1283 offsets
->switch_new_start
= 0;
1284 offsets
->switch_new_end
= 0;
1285 offsets
->switch_old_end
= 0;
1286 offsets
->pre_header_padding
= 0;
1288 ctx
->tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1289 if ((int64_t) ctx
->tsc
== -EIO
)
1292 if (last_tsc_overflow(config
, buf
, ctx
->tsc
))
1293 ctx
->rflags
|= RING_BUFFER_RFLAG_FULL_TSC
;
1295 if (caa_unlikely(subbuf_offset(offsets
->begin
, ctx
->chan
) == 0)) {
1296 offsets
->switch_new_start
= 1; /* For offsets->begin */
1298 offsets
->size
= config
->cb
.record_header_size(config
, chan
,
1300 &offsets
->pre_header_padding
,
1303 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1306 if (caa_unlikely(subbuf_offset(offsets
->begin
, chan
) +
1307 offsets
->size
> chan
->backend
.subbuf_size
)) {
1308 offsets
->switch_old_end
= 1; /* For offsets->old */
1309 offsets
->switch_new_start
= 1; /* For offsets->begin */
1312 if (caa_unlikely(offsets
->switch_new_start
)) {
1313 unsigned long sb_index
;
1316 * We are typically not filling the previous buffer completely.
1318 if (caa_likely(offsets
->switch_old_end
))
1319 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1320 offsets
->begin
= offsets
->begin
1321 + config
->cb
.subbuffer_header_size();
1322 /* Test new buffer integrity */
1323 sb_index
= subbuf_index(offsets
->begin
, chan
);
1324 reserve_commit_diff
=
1325 (buf_trunc(offsets
->begin
, chan
)
1326 >> chan
->backend
.num_subbuf_order
)
1327 - ((unsigned long) v_read(config
,
1328 &shmp_index(handle
, buf
->commit_cold
, sb_index
)->cc_sb
)
1329 & chan
->commit_count_mask
);
1330 if (caa_likely(reserve_commit_diff
== 0)) {
1331 /* Next subbuffer not being written to. */
1332 if (caa_unlikely(config
->mode
!= RING_BUFFER_OVERWRITE
&&
1333 subbuf_trunc(offsets
->begin
, chan
)
1334 - subbuf_trunc((unsigned long)
1335 uatomic_read(&buf
->consumed
), chan
)
1336 >= chan
->backend
.buf_size
)) {
1338 * We do not overwrite non consumed buffers
1339 * and we are full : record is lost.
1341 v_inc(config
, &buf
->records_lost_full
);
1345 * Next subbuffer not being written to, and we
1346 * are either in overwrite mode or the buffer is
1347 * not full. It's safe to write in this new
1353 * Next subbuffer reserve offset does not match the
1354 * commit offset. Drop record in producer-consumer and
1355 * overwrite mode. Caused by either a writer OOPS or too
1356 * many nested writes over a reserve/commit pair.
1358 v_inc(config
, &buf
->records_lost_wrap
);
1362 config
->cb
.record_header_size(config
, chan
,
1364 &offsets
->pre_header_padding
,
1367 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1370 if (caa_unlikely(subbuf_offset(offsets
->begin
, chan
)
1371 + offsets
->size
> chan
->backend
.subbuf_size
)) {
1373 * Record too big for subbuffers, report error, don't
1374 * complete the sub-buffer switch.
1376 v_inc(config
, &buf
->records_lost_big
);
1380 * We just made a successful buffer switch and the
1381 * record fits in the new subbuffer. Let's write.
1386 * Record fits in the current buffer and we are not on a switch
1387 * boundary. It's safe to write.
1390 offsets
->end
= offsets
->begin
+ offsets
->size
;
1392 if (caa_unlikely(subbuf_offset(offsets
->end
, chan
) == 0)) {
1394 * The offset_end will fall at the very beginning of the next
1397 offsets
->switch_new_end
= 1; /* For offsets->begin */
1403 * lib_ring_buffer_reserve_slow - Atomic slot reservation in a buffer.
1404 * @ctx: ring buffer context.
1406 * Return : -NOBUFS if not enough space, -ENOSPC if event size too large,
1407 * -EIO for other errors, else returns 0.
1408 * It will take care of sub-buffer switching.
1410 int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
1412 struct channel
*chan
= ctx
->chan
;
1413 struct lttng_ust_shm_handle
*handle
= ctx
->handle
;
1414 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1415 struct lttng_ust_lib_ring_buffer
*buf
;
1416 struct switch_offsets offsets
;
1419 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
1420 buf
= shmp(handle
, chan
->backend
.buf
[ctx
->cpu
].shmp
);
1422 buf
= shmp(handle
, chan
->backend
.buf
[0].shmp
);
1428 ret
= lib_ring_buffer_try_reserve_slow(buf
, chan
, &offsets
,
1430 if (caa_unlikely(ret
))
1432 } while (caa_unlikely(v_cmpxchg(config
, &buf
->offset
, offsets
.old
,
1437 * Atomically update last_tsc. This update races against concurrent
1438 * atomic updates, but the race will always cause supplementary full TSC
1439 * records, never the opposite (missing a full TSC record when it would
1442 save_last_tsc(config
, buf
, ctx
->tsc
);
1445 * Push the reader if necessary
1447 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.end
- 1);
1450 * Clear noref flag for this subbuffer.
1452 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
1453 subbuf_index(offsets
.end
- 1, chan
),
1457 * Switch old subbuffer if needed.
1459 if (caa_unlikely(offsets
.switch_old_end
)) {
1460 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
1461 subbuf_index(offsets
.old
- 1, chan
),
1463 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, ctx
->tsc
, handle
);
1467 * Populate new subbuffer.
1469 if (caa_unlikely(offsets
.switch_new_start
))
1470 lib_ring_buffer_switch_new_start(buf
, chan
, &offsets
, ctx
->tsc
, handle
);
1472 if (caa_unlikely(offsets
.switch_new_end
))
1473 lib_ring_buffer_switch_new_end(buf
, chan
, &offsets
, ctx
->tsc
, handle
);
1475 ctx
->slot_size
= offsets
.size
;
1476 ctx
->pre_offset
= offsets
.begin
;
1477 ctx
->buf_offset
= offsets
.begin
+ offsets
.pre_header_padding
;