2 * ring_buffer_frontend.c
4 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; only
9 * version 2.1 of the License.
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 * Ring buffer wait-free buffer synchronization. Producer-consumer and flight
22 * recorder (overwrite) modes. See thesis:
24 * Desnoyers, Mathieu (2009), "Low-Impact Operating System Tracing", Ph.D.
25 * dissertation, Ecole Polytechnique de Montreal.
26 * http://www.lttng.org/pub/thesis/desnoyers-dissertation-2009-12.pdf
28 * - Algorithm presentation in Chapter 5:
29 * "Lockless Multi-Core High-Throughput Buffering".
30 * - Algorithm formal verification in Section 8.6:
31 * "Formal verification of LTTng"
34 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
36 * Inspired from LTT and RelayFS:
37 * Karim Yaghmour <karim@opersys.com>
38 * Tom Zanussi <zanussi@us.ibm.com>
39 * Bob Wisniewski <bob@watson.ibm.com>
41 * Bob Wisniewski <bob@watson.ibm.com>
43 * Buffer reader semantic :
46 * while buffer is not finalized and empty
48 * - if return value != 0, continue
49 * - splice one subbuffer worth of data to a pipe
50 * - splice the data from pipe to disk/network
55 #include <sys/types.h>
62 #include <urcu/compiler.h>
64 #include <urcu/tls-compat.h>
68 #include <lttng/ringbuffer-config.h>
74 #include "../liblttng-ust/compat.h" /* For ENODATA */
77 #define max(a, b) ((a) > (b) ? (a) : (b))
80 /* Print DBG() messages about events lost only every 1048576 hits */
81 #define DBG_PRINT_NR_LOST (1UL << 20)
83 #define LTTNG_UST_RB_SIG SIGRTMIN
84 #define LTTNG_UST_RB_SIG_TEARDOWN SIGRTMIN + 1
85 #define CLOCKID CLOCK_MONOTONIC
88 * Use POSIX SHM: shm_open(3) and shm_unlink(3).
89 * close(2) to close the fd returned by shm_open.
90 * shm_unlink releases the shared memory object name.
91 * ftruncate(2) sets the size of the memory object.
92 * mmap/munmap maps the shared memory obj to a virtual address in the
93 * calling proceess (should be done both in libust and consumer).
94 * See shm_overview(7) for details.
95 * Pass file descriptor returned by shm_open(3) to ltt-sessiond through
98 * Since we don't need to access the object using its name, we can
99 * immediately shm_unlink(3) it, and only keep the handle with its file
104 * Internal structure representing offsets to use at a sub-buffer switch.
106 struct switch_offsets
{
107 unsigned long begin
, end
, old
;
108 size_t pre_header_padding
, size
;
109 unsigned int switch_new_start
:1, switch_new_end
:1, switch_old_start
:1,
113 DEFINE_URCU_TLS(unsigned int, lib_ring_buffer_nesting
);
116 void lib_ring_buffer_print_errors(struct channel
*chan
,
117 struct lttng_ust_lib_ring_buffer
*buf
, int cpu
,
118 struct lttng_ust_shm_handle
*handle
);
121 * Handle timer teardown race wrt memory free of private data by
122 * ring buffer signals are handled by a single thread, which permits
123 * a synchronization point between handling of each signal.
124 * Protected by the ust mutex.
126 struct timer_signal_data
{
127 pthread_t tid
; /* thread id managing signals */
132 static struct timer_signal_data timer_signal
;
135 * lib_ring_buffer_reset - Reset ring buffer to initial values.
138 * Effectively empty the ring buffer. Should be called when the buffer is not
139 * used for writing. The ring buffer can be opened for reading, but the reader
140 * should not be using the iterator concurrently with reset. The previous
141 * current iterator record is reset.
143 void lib_ring_buffer_reset(struct lttng_ust_lib_ring_buffer
*buf
,
144 struct lttng_ust_shm_handle
*handle
)
146 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
147 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
151 * Reset iterator first. It will put the subbuffer if it currently holds
154 v_set(config
, &buf
->offset
, 0);
155 for (i
= 0; i
< chan
->backend
.num_subbuf
; i
++) {
156 v_set(config
, &shmp_index(handle
, buf
->commit_hot
, i
)->cc
, 0);
157 v_set(config
, &shmp_index(handle
, buf
->commit_hot
, i
)->seq
, 0);
158 v_set(config
, &shmp_index(handle
, buf
->commit_cold
, i
)->cc_sb
, 0);
160 uatomic_set(&buf
->consumed
, 0);
161 uatomic_set(&buf
->record_disabled
, 0);
162 v_set(config
, &buf
->last_tsc
, 0);
163 lib_ring_buffer_backend_reset(&buf
->backend
, handle
);
164 /* Don't reset number of active readers */
165 v_set(config
, &buf
->records_lost_full
, 0);
166 v_set(config
, &buf
->records_lost_wrap
, 0);
167 v_set(config
, &buf
->records_lost_big
, 0);
168 v_set(config
, &buf
->records_count
, 0);
169 v_set(config
, &buf
->records_overrun
, 0);
174 * channel_reset - Reset channel to initial values.
177 * Effectively empty the channel. Should be called when the channel is not used
178 * for writing. The channel can be opened for reading, but the reader should not
179 * be using the iterator concurrently with reset. The previous current iterator
182 void channel_reset(struct channel
*chan
)
185 * Reset iterators first. Will put the subbuffer if held for reading.
187 uatomic_set(&chan
->record_disabled
, 0);
188 /* Don't reset commit_count_mask, still valid */
189 channel_backend_reset(&chan
->backend
);
190 /* Don't reset switch/read timer interval */
191 /* Don't reset notifiers and notifier enable bits */
192 /* Don't reset reader reference count */
196 * Must be called under cpu hotplug protection.
198 int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer
*buf
,
199 struct channel_backend
*chanb
, int cpu
,
200 struct lttng_ust_shm_handle
*handle
,
201 struct shm_object
*shmobj
)
203 const struct lttng_ust_lib_ring_buffer_config
*config
= &chanb
->config
;
204 struct channel
*chan
= caa_container_of(chanb
, struct channel
, backend
);
205 void *priv
= channel_get_private(chan
);
206 size_t subbuf_header_size
;
210 /* Test for cpu hotplug */
211 if (buf
->backend
.allocated
)
214 ret
= lib_ring_buffer_backend_create(&buf
->backend
, &chan
->backend
,
215 cpu
, handle
, shmobj
);
219 align_shm(shmobj
, __alignof__(struct commit_counters_hot
));
220 set_shmp(buf
->commit_hot
,
222 sizeof(struct commit_counters_hot
) * chan
->backend
.num_subbuf
));
223 if (!shmp(handle
, buf
->commit_hot
)) {
228 align_shm(shmobj
, __alignof__(struct commit_counters_cold
));
229 set_shmp(buf
->commit_cold
,
231 sizeof(struct commit_counters_cold
) * chan
->backend
.num_subbuf
));
232 if (!shmp(handle
, buf
->commit_cold
)) {
238 * Write the subbuffer header for first subbuffer so we know the total
239 * duration of data gathering.
241 subbuf_header_size
= config
->cb
.subbuffer_header_size();
242 v_set(config
, &buf
->offset
, subbuf_header_size
);
243 subbuffer_id_clear_noref(config
, &shmp_index(handle
, buf
->backend
.buf_wsb
, 0)->id
);
244 tsc
= config
->cb
.ring_buffer_clock_read(shmp(handle
, buf
->backend
.chan
));
245 config
->cb
.buffer_begin(buf
, tsc
, 0, handle
);
246 v_add(config
, subbuf_header_size
, &shmp_index(handle
, buf
->commit_hot
, 0)->cc
);
248 if (config
->cb
.buffer_create
) {
249 ret
= config
->cb
.buffer_create(buf
, priv
, cpu
, chanb
->name
, handle
);
253 buf
->backend
.allocated
= 1;
258 /* commit_cold will be freed by shm teardown */
260 /* commit_hot will be freed by shm teardown */
266 static void switch_buffer_timer(unsigned long data
)
268 struct lttng_ust_lib_ring_buffer
*buf
= (struct lttng_ust_lib_ring_buffer
*)data
;
269 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
270 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
273 * Only flush buffers periodically if readers are active.
275 if (uatomic_read(&buf
->active_readers
))
276 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
, handle
);
279 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
280 // mod_timer_pinned(&buf->switch_timer,
281 // jiffies + chan->switch_timer_interval);
283 // mod_timer(&buf->switch_timer,
284 // jiffies + chan->switch_timer_interval);
289 void lib_ring_buffer_channel_switch_timer(int sig
, siginfo_t
*si
, void *uc
)
291 const struct lttng_ust_lib_ring_buffer_config
*config
;
292 struct lttng_ust_shm_handle
*handle
;
293 struct channel
*chan
;
296 assert(CMM_LOAD_SHARED(timer_signal
.tid
) == pthread_self());
298 chan
= si
->si_value
.sival_ptr
;
299 handle
= chan
->handle
;
300 config
= &chan
->backend
.config
;
302 DBG("Timer for channel %p\n", chan
);
304 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
305 for_each_possible_cpu(cpu
) {
306 struct lttng_ust_lib_ring_buffer
*buf
=
307 shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
309 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
,
313 struct lttng_ust_lib_ring_buffer
*buf
=
314 shmp(handle
, chan
->backend
.buf
[0].shmp
);
316 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
,
323 void rb_setmask(sigset_t
*mask
)
327 ret
= sigemptyset(mask
);
329 PERROR("sigemptyset");
331 ret
= sigaddset(mask
, LTTNG_UST_RB_SIG
);
335 ret
= sigaddset(mask
, LTTNG_UST_RB_SIG_TEARDOWN
);
342 void *sig_thread(void *arg
)
348 /* Only self thread will receive signal mask. */
350 CMM_STORE_SHARED(timer_signal
.tid
, pthread_self());
353 signr
= sigwaitinfo(&mask
, &info
);
355 PERROR("sigwaitinfo");
358 if (signr
== LTTNG_UST_RB_SIG
) {
359 lib_ring_buffer_channel_switch_timer(info
.si_signo
,
361 } else if (signr
== LTTNG_UST_RB_SIG_TEARDOWN
) {
363 CMM_STORE_SHARED(timer_signal
.qs_done
, 1);
366 ERR("Unexptected signal %d\n", info
.si_signo
);
373 * Called with ust_lock() held.
374 * Ensure only a single thread listens on the timer signal.
377 void lib_ring_buffer_setup_timer_thread(void)
382 if (timer_signal
.setup_done
)
385 ret
= pthread_create(&thread
, NULL
, &sig_thread
, NULL
);
388 PERROR("pthread_create");
390 ret
= pthread_detach(thread
);
393 PERROR("pthread_detach");
395 timer_signal
.setup_done
= 1;
399 * Called with ust_lock() held.
402 void lib_ring_buffer_channel_switch_timer_start(struct channel
*chan
)
405 struct itimerspec its
;
408 if (!chan
->switch_timer_interval
|| chan
->switch_timer_enabled
)
411 chan
->switch_timer_enabled
= 1;
413 lib_ring_buffer_setup_timer_thread();
415 sev
.sigev_notify
= SIGEV_SIGNAL
;
416 sev
.sigev_signo
= LTTNG_UST_RB_SIG
;
417 sev
.sigev_value
.sival_ptr
= chan
;
418 ret
= timer_create(CLOCKID
, &sev
, &chan
->switch_timer
);
420 PERROR("timer_create");
423 its
.it_value
.tv_sec
= chan
->switch_timer_interval
/ 1000000;
424 its
.it_value
.tv_nsec
= chan
->switch_timer_interval
% 1000000;
425 its
.it_interval
.tv_sec
= its
.it_value
.tv_sec
;
426 its
.it_interval
.tv_nsec
= its
.it_value
.tv_nsec
;
428 ret
= timer_settime(chan
->switch_timer
, 0, &its
, NULL
);
430 PERROR("timer_settime");
435 * Called with ust_lock() held.
438 void lib_ring_buffer_channel_switch_timer_stop(struct channel
*chan
)
440 sigset_t pending_set
;
441 int sig_is_pending
, ret
;
443 if (!chan
->switch_timer_interval
|| !chan
->switch_timer_enabled
)
446 ret
= timer_delete(chan
->switch_timer
);
448 PERROR("timer_delete");
452 * Ensure we don't have any signal queued for this channel.
455 ret
= sigemptyset(&pending_set
);
457 PERROR("sigemptyset");
459 ret
= sigpending(&pending_set
);
461 PERROR("sigpending");
463 sig_is_pending
= sigismember(&pending_set
, LTTNG_UST_RB_SIG
);
470 * From this point, no new signal handler will be fired that
471 * would try to access "chan". However, we still need to wait
472 * for any currently executing handler to complete.
475 CMM_STORE_SHARED(timer_signal
.qs_done
, 0);
479 * Kill with LTTNG_UST_RB_SIG_TEARDOWN, so signal management
482 kill(getpid(), LTTNG_UST_RB_SIG_TEARDOWN
);
484 while (!CMM_LOAD_SHARED(timer_signal
.qs_done
))
488 chan
->switch_timer
= 0;
489 chan
->switch_timer_enabled
= 0;
494 * Polling timer to check the channels for data.
496 static void read_buffer_timer(unsigned long data
)
498 struct lttng_ust_lib_ring_buffer
*buf
= (struct lttng_ust_lib_ring_buffer
*)data
;
499 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
500 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
502 CHAN_WARN_ON(chan
, !buf
->backend
.allocated
);
504 if (uatomic_read(&buf
->active_readers
))
505 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
507 //wake_up_interruptible(&buf->read_wait);
508 //wake_up_interruptible(&chan->read_wait);
512 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
513 // mod_timer_pinned(&buf->read_timer,
514 // jiffies + chan->read_timer_interval);
516 // mod_timer(&buf->read_timer,
517 // jiffies + chan->read_timer_interval);
521 static void lib_ring_buffer_start_read_timer(struct lttng_ust_lib_ring_buffer
*buf
,
522 struct lttng_ust_shm_handle
*handle
)
524 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
525 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
527 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
528 || !chan
->read_timer_interval
529 || buf
->read_timer_enabled
)
533 //init_timer(&buf->read_timer);
534 //buf->read_timer.function = read_buffer_timer;
535 //buf->read_timer.expires = jiffies + chan->read_timer_interval;
536 //buf->read_timer.data = (unsigned long)buf;
538 //if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
539 // add_timer_on(&buf->read_timer, buf->backend.cpu);
541 // add_timer(&buf->read_timer);
542 buf
->read_timer_enabled
= 1;
545 static void lib_ring_buffer_stop_read_timer(struct lttng_ust_lib_ring_buffer
*buf
,
546 struct lttng_ust_shm_handle
*handle
)
548 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
549 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
551 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
552 || !chan
->read_timer_interval
553 || !buf
->read_timer_enabled
)
557 //del_timer_sync(&buf->read_timer);
559 * do one more check to catch data that has been written in the last
562 if (lib_ring_buffer_poll_deliver(config
, buf
, chan
, handle
)) {
564 //wake_up_interruptible(&buf->read_wait);
565 //wake_up_interruptible(&chan->read_wait);
567 buf
->read_timer_enabled
= 0;
570 static void channel_unregister_notifiers(struct channel
*chan
,
571 struct lttng_ust_shm_handle
*handle
)
573 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
576 lib_ring_buffer_channel_switch_timer_stop(chan
);
577 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
578 for_each_possible_cpu(cpu
) {
579 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
581 lib_ring_buffer_stop_read_timer(buf
, handle
);
584 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[0].shmp
);
586 lib_ring_buffer_stop_read_timer(buf
, handle
);
588 //channel_backend_unregister_notifiers(&chan->backend);
591 static void channel_print_errors(struct channel
*chan
,
592 struct lttng_ust_shm_handle
*handle
)
594 const struct lttng_ust_lib_ring_buffer_config
*config
=
595 &chan
->backend
.config
;
598 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
599 for_each_possible_cpu(cpu
) {
600 struct lttng_ust_lib_ring_buffer
*buf
=
601 shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
602 lib_ring_buffer_print_errors(chan
, buf
, cpu
, handle
);
605 struct lttng_ust_lib_ring_buffer
*buf
=
606 shmp(handle
, chan
->backend
.buf
[0].shmp
);
608 lib_ring_buffer_print_errors(chan
, buf
, -1, handle
);
612 static void channel_free(struct channel
*chan
,
613 struct lttng_ust_shm_handle
*handle
)
615 channel_backend_free(&chan
->backend
, handle
);
616 /* chan is freed by shm teardown */
617 shm_object_table_destroy(handle
->table
);
622 * channel_create - Create channel.
623 * @config: ring buffer instance configuration
624 * @name: name of the channel
625 * @priv_data: ring buffer client private data area pointer (output)
626 * @priv_data_size: length, in bytes, of the private data area.
627 * @priv_data_init: initialization data for private data.
628 * @buf_addr: pointer the the beginning of the preallocated buffer contiguous
629 * address mapping. It is used only by RING_BUFFER_STATIC
630 * configuration. It can be set to NULL for other backends.
631 * @subbuf_size: subbuffer size
632 * @num_subbuf: number of subbuffers
633 * @switch_timer_interval: Time interval (in us) to fill sub-buffers with
634 * padding to let readers get those sub-buffers.
635 * Used for live streaming.
636 * @read_timer_interval: Time interval (in us) to wake up pending readers.
639 * Returns NULL on failure.
641 struct lttng_ust_shm_handle
*channel_create(const struct lttng_ust_lib_ring_buffer_config
*config
,
644 size_t priv_data_align
,
645 size_t priv_data_size
,
646 void *priv_data_init
,
647 void *buf_addr
, size_t subbuf_size
,
648 size_t num_subbuf
, unsigned int switch_timer_interval
,
649 unsigned int read_timer_interval
)
652 size_t shmsize
, chansize
;
653 struct channel
*chan
;
654 struct lttng_ust_shm_handle
*handle
;
655 struct shm_object
*shmobj
;
656 unsigned int nr_streams
;
658 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
659 nr_streams
= num_possible_cpus();
663 if (lib_ring_buffer_check_config(config
, switch_timer_interval
,
664 read_timer_interval
))
667 handle
= zmalloc(sizeof(struct lttng_ust_shm_handle
));
671 /* Allocate table for channel + per-cpu buffers */
672 handle
->table
= shm_object_table_create(1 + num_possible_cpus());
674 goto error_table_alloc
;
676 /* Calculate the shm allocation layout */
677 shmsize
= sizeof(struct channel
);
678 shmsize
+= offset_align(shmsize
, __alignof__(struct lttng_ust_lib_ring_buffer_shmp
));
679 shmsize
+= sizeof(struct lttng_ust_lib_ring_buffer_shmp
) * nr_streams
;
682 shmsize
+= offset_align(shmsize
, priv_data_align
);
683 shmsize
+= priv_data_size
;
685 /* Allocate normal memory for channel (not shared) */
686 shmobj
= shm_object_table_alloc(handle
->table
, shmsize
, SHM_OBJECT_MEM
);
689 /* struct channel is at object 0, offset 0 (hardcoded) */
690 set_shmp(handle
->chan
, zalloc_shm(shmobj
, chansize
));
691 assert(handle
->chan
._ref
.index
== 0);
692 assert(handle
->chan
._ref
.offset
== 0);
693 chan
= shmp(handle
, handle
->chan
);
696 chan
->nr_streams
= nr_streams
;
698 /* space for private data */
699 if (priv_data_size
) {
700 DECLARE_SHMP(void, priv_data_alloc
);
702 align_shm(shmobj
, priv_data_align
);
703 chan
->priv_data_offset
= shmobj
->allocated_len
;
704 set_shmp(priv_data_alloc
, zalloc_shm(shmobj
, priv_data_size
));
705 if (!shmp(handle
, priv_data_alloc
))
707 *priv_data
= channel_get_private(chan
);
708 memcpy(*priv_data
, priv_data_init
, priv_data_size
);
710 chan
->priv_data_offset
= -1;
715 ret
= channel_backend_init(&chan
->backend
, name
, config
,
716 subbuf_size
, num_subbuf
, handle
);
718 goto error_backend_init
;
720 chan
->handle
= handle
;
721 chan
->commit_count_mask
= (~0UL >> chan
->backend
.num_subbuf_order
);
722 chan
->switch_timer_interval
= switch_timer_interval
;
725 //chan->read_timer_interval = read_timer_interval;
726 //init_waitqueue_head(&chan->read_wait);
727 //init_waitqueue_head(&chan->hp_wait);
729 lib_ring_buffer_channel_switch_timer_start(chan
);
730 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
732 * In case of non-hotplug cpu, if the ring-buffer is allocated
733 * in early initcall, it will not be notified of secondary cpus.
734 * In that off case, we need to allocate for all possible cpus.
736 for_each_possible_cpu(cpu
) {
737 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
738 lib_ring_buffer_start_read_timer(buf
, handle
);
741 struct lttng_ust_lib_ring_buffer
*buf
= shmp(handle
, chan
->backend
.buf
[0].shmp
);
743 lib_ring_buffer_start_read_timer(buf
, handle
);
749 shm_object_table_destroy(handle
->table
);
755 struct lttng_ust_shm_handle
*channel_handle_create(void *data
,
756 uint64_t memory_map_size
,
759 struct lttng_ust_shm_handle
*handle
;
760 struct shm_object
*object
;
762 handle
= zmalloc(sizeof(struct lttng_ust_shm_handle
));
766 /* Allocate table for channel + per-cpu buffers */
767 handle
->table
= shm_object_table_create(1 + num_possible_cpus());
769 goto error_table_alloc
;
770 /* Add channel object */
771 object
= shm_object_table_append_mem(handle
->table
, data
,
772 memory_map_size
, wakeup_fd
);
774 goto error_table_object
;
775 /* struct channel is at object 0, offset 0 (hardcoded) */
776 handle
->chan
._ref
.index
= 0;
777 handle
->chan
._ref
.offset
= 0;
781 shm_object_table_destroy(handle
->table
);
787 int channel_handle_add_stream(struct lttng_ust_shm_handle
*handle
,
788 int shm_fd
, int wakeup_fd
, uint32_t stream_nr
,
789 uint64_t memory_map_size
)
791 struct shm_object
*object
;
793 /* Add stream object */
794 object
= shm_object_table_append_shm(handle
->table
,
795 shm_fd
, wakeup_fd
, stream_nr
,
802 unsigned int channel_handle_get_nr_streams(struct lttng_ust_shm_handle
*handle
)
804 assert(handle
->table
);
805 return handle
->table
->allocated_len
- 1;
809 void channel_release(struct channel
*chan
, struct lttng_ust_shm_handle
*handle
)
811 channel_free(chan
, handle
);
815 * channel_destroy - Finalize, wait for q.s. and destroy channel.
816 * @chan: channel to destroy
819 * Call "destroy" callback, finalize channels, decrement the channel
820 * reference count. Note that when readers have completed data
821 * consumption of finalized channels, get_subbuf() will return -ENODATA.
822 * They should release their handle at that point.
824 void channel_destroy(struct channel
*chan
, struct lttng_ust_shm_handle
*handle
,
829 * Note: the consumer takes care of finalizing and
830 * switching the buffers.
832 channel_unregister_notifiers(chan
, handle
);
834 * The consumer prints errors.
836 channel_print_errors(chan
, handle
);
840 * sessiond/consumer are keeping a reference on the shm file
841 * descriptor directly. No need to refcount.
843 channel_release(chan
, handle
);
847 struct lttng_ust_lib_ring_buffer
*channel_get_ring_buffer(
848 const struct lttng_ust_lib_ring_buffer_config
*config
,
849 struct channel
*chan
, int cpu
,
850 struct lttng_ust_shm_handle
*handle
,
851 int *shm_fd
, int *wait_fd
,
853 uint64_t *memory_map_size
)
857 if (config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
) {
860 if (cpu
>= num_possible_cpus())
863 ref
= &chan
->backend
.buf
[cpu
].shmp
._ref
;
864 *shm_fd
= shm_get_shm_fd(handle
, ref
);
865 *wait_fd
= shm_get_wait_fd(handle
, ref
);
866 *wakeup_fd
= shm_get_wakeup_fd(handle
, ref
);
867 if (shm_get_shm_size(handle
, ref
, memory_map_size
))
869 return shmp(handle
, chan
->backend
.buf
[cpu
].shmp
);
872 int ring_buffer_channel_close_wait_fd(const struct lttng_ust_lib_ring_buffer_config
*config
,
873 struct channel
*chan
,
874 struct lttng_ust_shm_handle
*handle
)
878 ref
= &handle
->chan
._ref
;
879 return shm_close_wait_fd(handle
, ref
);
882 int ring_buffer_channel_close_wakeup_fd(const struct lttng_ust_lib_ring_buffer_config
*config
,
883 struct channel
*chan
,
884 struct lttng_ust_shm_handle
*handle
)
888 ref
= &handle
->chan
._ref
;
889 return shm_close_wakeup_fd(handle
, ref
);
892 int ring_buffer_stream_close_wait_fd(const struct lttng_ust_lib_ring_buffer_config
*config
,
893 struct channel
*chan
,
894 struct lttng_ust_shm_handle
*handle
,
899 if (config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
) {
902 if (cpu
>= num_possible_cpus())
905 ref
= &chan
->backend
.buf
[cpu
].shmp
._ref
;
906 return shm_close_wait_fd(handle
, ref
);
909 int ring_buffer_stream_close_wakeup_fd(const struct lttng_ust_lib_ring_buffer_config
*config
,
910 struct channel
*chan
,
911 struct lttng_ust_shm_handle
*handle
,
916 if (config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
) {
919 if (cpu
>= num_possible_cpus())
922 ref
= &chan
->backend
.buf
[cpu
].shmp
._ref
;
923 return shm_close_wakeup_fd(handle
, ref
);
926 int lib_ring_buffer_open_read(struct lttng_ust_lib_ring_buffer
*buf
,
927 struct lttng_ust_shm_handle
*handle
)
929 if (uatomic_cmpxchg(&buf
->active_readers
, 0, 1) != 0)
935 void lib_ring_buffer_release_read(struct lttng_ust_lib_ring_buffer
*buf
,
936 struct lttng_ust_shm_handle
*handle
)
938 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
940 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_readers
) != 1);
942 uatomic_dec(&buf
->active_readers
);
946 * lib_ring_buffer_snapshot - save subbuffer position snapshot (for read)
948 * @consumed: consumed count indicating the position where to read
949 * @produced: produced count, indicates position when to stop reading
951 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
952 * data to read at consumed position, or 0 if the get operation succeeds.
955 int lib_ring_buffer_snapshot(struct lttng_ust_lib_ring_buffer
*buf
,
956 unsigned long *consumed
, unsigned long *produced
,
957 struct lttng_ust_shm_handle
*handle
)
959 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
960 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
961 unsigned long consumed_cur
, write_offset
;
964 finalized
= CMM_ACCESS_ONCE(buf
->finalized
);
966 * Read finalized before counters.
969 consumed_cur
= uatomic_read(&buf
->consumed
);
971 * No need to issue a memory barrier between consumed count read and
972 * write offset read, because consumed count can only change
973 * concurrently in overwrite mode, and we keep a sequence counter
974 * identifier derived from the write offset to check we are getting
975 * the same sub-buffer we are expecting (the sub-buffers are atomically
976 * "tagged" upon writes, tags are checked upon read).
978 write_offset
= v_read(config
, &buf
->offset
);
981 * Check that we are not about to read the same subbuffer in
982 * which the writer head is.
984 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_cur
, chan
)
988 *consumed
= consumed_cur
;
989 *produced
= subbuf_trunc(write_offset
, chan
);
995 * The memory barriers __wait_event()/wake_up_interruptible() take care
996 * of "raw_spin_is_locked" memory ordering.
1005 * lib_ring_buffer_put_snapshot - move consumed counter forward
1007 * @consumed_new: new consumed count value
1009 void lib_ring_buffer_move_consumer(struct lttng_ust_lib_ring_buffer
*buf
,
1010 unsigned long consumed_new
,
1011 struct lttng_ust_shm_handle
*handle
)
1013 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &buf
->backend
;
1014 struct channel
*chan
= shmp(handle
, bufb
->chan
);
1015 unsigned long consumed
;
1017 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_readers
) != 1);
1020 * Only push the consumed value forward.
1021 * If the consumed cmpxchg fails, this is because we have been pushed by
1022 * the writer in flight recorder mode.
1024 consumed
= uatomic_read(&buf
->consumed
);
1025 while ((long) consumed
- (long) consumed_new
< 0)
1026 consumed
= uatomic_cmpxchg(&buf
->consumed
, consumed
,
1031 * lib_ring_buffer_get_subbuf - get exclusive access to subbuffer for reading
1033 * @consumed: consumed count indicating the position where to read
1035 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
1036 * data to read at consumed position, or 0 if the get operation succeeds.
1038 int lib_ring_buffer_get_subbuf(struct lttng_ust_lib_ring_buffer
*buf
,
1039 unsigned long consumed
,
1040 struct lttng_ust_shm_handle
*handle
)
1042 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
1043 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1044 unsigned long consumed_cur
, consumed_idx
, commit_count
, write_offset
;
1049 finalized
= CMM_ACCESS_ONCE(buf
->finalized
);
1051 * Read finalized before counters.
1054 consumed_cur
= uatomic_read(&buf
->consumed
);
1055 consumed_idx
= subbuf_index(consumed
, chan
);
1056 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_cold
, consumed_idx
)->cc_sb
);
1058 * Make sure we read the commit count before reading the buffer
1059 * data and the write offset. Correct consumed offset ordering
1060 * wrt commit count is insured by the use of cmpxchg to update
1061 * the consumed offset.
1064 * Local rmb to match the remote wmb to read the commit count
1065 * before the buffer data and the write offset.
1069 write_offset
= v_read(config
, &buf
->offset
);
1072 * Check that the buffer we are getting is after or at consumed_cur
1075 if ((long) subbuf_trunc(consumed
, chan
)
1076 - (long) subbuf_trunc(consumed_cur
, chan
) < 0)
1080 * Check that the subbuffer we are trying to consume has been
1081 * already fully committed.
1083 if (((commit_count
- chan
->backend
.subbuf_size
)
1084 & chan
->commit_count_mask
)
1085 - (buf_trunc(consumed_cur
, chan
)
1086 >> chan
->backend
.num_subbuf_order
)
1091 * Check that we are not about to read the same subbuffer in
1092 * which the writer head is.
1094 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_cur
, chan
)
1099 * Failure to get the subbuffer causes a busy-loop retry without going
1100 * to a wait queue. These are caused by short-lived race windows where
1101 * the writer is getting access to a subbuffer we were trying to get
1102 * access to. Also checks that the "consumed" buffer count we are
1103 * looking for matches the one contained in the subbuffer id.
1105 ret
= update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
1106 consumed_idx
, buf_trunc_val(consumed
, chan
),
1110 subbuffer_id_clear_noref(config
, &buf
->backend
.buf_rsb
.id
);
1112 buf
->get_subbuf_consumed
= consumed
;
1113 buf
->get_subbuf
= 1;
1119 * The memory barriers __wait_event()/wake_up_interruptible() take care
1120 * of "raw_spin_is_locked" memory ordering.
1129 * lib_ring_buffer_put_subbuf - release exclusive subbuffer access
1132 void lib_ring_buffer_put_subbuf(struct lttng_ust_lib_ring_buffer
*buf
,
1133 struct lttng_ust_shm_handle
*handle
)
1135 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &buf
->backend
;
1136 struct channel
*chan
= shmp(handle
, bufb
->chan
);
1137 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1138 unsigned long read_sb_bindex
, consumed_idx
, consumed
;
1140 CHAN_WARN_ON(chan
, uatomic_read(&buf
->active_readers
) != 1);
1142 if (!buf
->get_subbuf
) {
1144 * Reader puts a subbuffer it did not get.
1146 CHAN_WARN_ON(chan
, 1);
1149 consumed
= buf
->get_subbuf_consumed
;
1150 buf
->get_subbuf
= 0;
1153 * Clear the records_unread counter. (overruns counter)
1154 * Can still be non-zero if a file reader simply grabbed the data
1155 * without using iterators.
1156 * Can be below zero if an iterator is used on a snapshot more than
1159 read_sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
1160 v_add(config
, v_read(config
,
1161 &shmp(handle
, shmp_index(handle
, bufb
->array
, read_sb_bindex
)->shmp
)->records_unread
),
1162 &bufb
->records_read
);
1163 v_set(config
, &shmp(handle
, shmp_index(handle
, bufb
->array
, read_sb_bindex
)->shmp
)->records_unread
, 0);
1164 CHAN_WARN_ON(chan
, config
->mode
== RING_BUFFER_OVERWRITE
1165 && subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
1166 subbuffer_id_set_noref(config
, &bufb
->buf_rsb
.id
);
1169 * Exchange the reader subbuffer with the one we put in its place in the
1170 * writer subbuffer table. Expect the original consumed count. If
1171 * update_read_sb_index fails, this is because the writer updated the
1172 * subbuffer concurrently. We should therefore keep the subbuffer we
1173 * currently have: it has become invalid to try reading this sub-buffer
1174 * consumed count value anyway.
1176 consumed_idx
= subbuf_index(consumed
, chan
);
1177 update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
1178 consumed_idx
, buf_trunc_val(consumed
, chan
),
1181 * update_read_sb_index return value ignored. Don't exchange sub-buffer
1182 * if the writer concurrently updated it.
1187 * cons_offset is an iterator on all subbuffer offsets between the reader
1188 * position and the writer position. (inclusive)
1191 void lib_ring_buffer_print_subbuffer_errors(struct lttng_ust_lib_ring_buffer
*buf
,
1192 struct channel
*chan
,
1193 unsigned long cons_offset
,
1195 struct lttng_ust_shm_handle
*handle
)
1197 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1198 unsigned long cons_idx
, commit_count
, commit_count_sb
;
1200 cons_idx
= subbuf_index(cons_offset
, chan
);
1201 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, cons_idx
)->cc
);
1202 commit_count_sb
= v_read(config
, &shmp_index(handle
, buf
->commit_cold
, cons_idx
)->cc_sb
);
1204 if (subbuf_offset(commit_count
, chan
) != 0)
1205 DBG("ring buffer %s, cpu %d: "
1206 "commit count in subbuffer %lu,\n"
1207 "expecting multiples of %lu bytes\n"
1208 " [ %lu bytes committed, %lu bytes reader-visible ]\n",
1209 chan
->backend
.name
, cpu
, cons_idx
,
1210 chan
->backend
.subbuf_size
,
1211 commit_count
, commit_count_sb
);
1213 DBG("ring buffer: %s, cpu %d: %lu bytes committed\n",
1214 chan
->backend
.name
, cpu
, commit_count
);
1218 void lib_ring_buffer_print_buffer_errors(struct lttng_ust_lib_ring_buffer
*buf
,
1219 struct channel
*chan
,
1220 void *priv
, int cpu
,
1221 struct lttng_ust_shm_handle
*handle
)
1223 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1224 unsigned long write_offset
, cons_offset
;
1227 * No need to order commit_count, write_offset and cons_offset reads
1228 * because we execute at teardown when no more writer nor reader
1229 * references are left.
1231 write_offset
= v_read(config
, &buf
->offset
);
1232 cons_offset
= uatomic_read(&buf
->consumed
);
1233 if (write_offset
!= cons_offset
)
1234 DBG("ring buffer %s, cpu %d: "
1235 "non-consumed data\n"
1236 " [ %lu bytes written, %lu bytes read ]\n",
1237 chan
->backend
.name
, cpu
, write_offset
, cons_offset
);
1239 for (cons_offset
= uatomic_read(&buf
->consumed
);
1240 (long) (subbuf_trunc((unsigned long) v_read(config
, &buf
->offset
),
1243 cons_offset
= subbuf_align(cons_offset
, chan
))
1244 lib_ring_buffer_print_subbuffer_errors(buf
, chan
, cons_offset
,
1249 void lib_ring_buffer_print_errors(struct channel
*chan
,
1250 struct lttng_ust_lib_ring_buffer
*buf
, int cpu
,
1251 struct lttng_ust_shm_handle
*handle
)
1253 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1254 void *priv
= channel_get_private(chan
);
1256 if (!strcmp(chan
->backend
.name
, "relay-metadata-mmap")) {
1257 DBG("ring buffer %s: %lu records written, "
1258 "%lu records overrun\n",
1260 v_read(config
, &buf
->records_count
),
1261 v_read(config
, &buf
->records_overrun
));
1263 DBG("ring buffer %s, cpu %d: %lu records written, "
1264 "%lu records overrun\n",
1265 chan
->backend
.name
, cpu
,
1266 v_read(config
, &buf
->records_count
),
1267 v_read(config
, &buf
->records_overrun
));
1269 if (v_read(config
, &buf
->records_lost_full
)
1270 || v_read(config
, &buf
->records_lost_wrap
)
1271 || v_read(config
, &buf
->records_lost_big
))
1272 DBG("ring buffer %s, cpu %d: records were lost. Caused by:\n"
1273 " [ %lu buffer full, %lu nest buffer wrap-around, "
1274 "%lu event too big ]\n",
1275 chan
->backend
.name
, cpu
,
1276 v_read(config
, &buf
->records_lost_full
),
1277 v_read(config
, &buf
->records_lost_wrap
),
1278 v_read(config
, &buf
->records_lost_big
));
1280 lib_ring_buffer_print_buffer_errors(buf
, chan
, priv
, cpu
, handle
);
1284 * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
1286 * Only executed when the buffer is finalized, in SWITCH_FLUSH.
1289 void lib_ring_buffer_switch_old_start(struct lttng_ust_lib_ring_buffer
*buf
,
1290 struct channel
*chan
,
1291 struct switch_offsets
*offsets
,
1293 struct lttng_ust_shm_handle
*handle
)
1295 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1296 unsigned long oldidx
= subbuf_index(offsets
->old
, chan
);
1297 unsigned long commit_count
;
1299 config
->cb
.buffer_begin(buf
, tsc
, oldidx
, handle
);
1302 * Order all writes to buffer before the commit count update that will
1303 * determine that the subbuffer is full.
1306 v_add(config
, config
->cb
.subbuffer_header_size(),
1307 &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1308 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1309 /* Check if the written buffer has to be delivered */
1310 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
,
1311 commit_count
, oldidx
, handle
);
1312 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, oldidx
,
1313 offsets
->old
, commit_count
,
1314 config
->cb
.subbuffer_header_size(),
1319 * lib_ring_buffer_switch_old_end: switch old subbuffer
1321 * Note : offset_old should never be 0 here. It is ok, because we never perform
1322 * buffer switch on an empty subbuffer in SWITCH_ACTIVE mode. The caller
1323 * increments the offset_old value when doing a SWITCH_FLUSH on an empty
1327 void lib_ring_buffer_switch_old_end(struct lttng_ust_lib_ring_buffer
*buf
,
1328 struct channel
*chan
,
1329 struct switch_offsets
*offsets
,
1331 struct lttng_ust_shm_handle
*handle
)
1333 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1334 unsigned long oldidx
= subbuf_index(offsets
->old
- 1, chan
);
1335 unsigned long commit_count
, padding_size
, data_size
;
1337 data_size
= subbuf_offset(offsets
->old
- 1, chan
) + 1;
1338 padding_size
= chan
->backend
.subbuf_size
- data_size
;
1339 subbuffer_set_data_size(config
, &buf
->backend
, oldidx
, data_size
,
1343 * Order all writes to buffer before the commit count update that will
1344 * determine that the subbuffer is full.
1347 v_add(config
, padding_size
, &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1348 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, oldidx
)->cc
);
1349 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
- 1,
1350 commit_count
, oldidx
, handle
);
1351 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, oldidx
,
1352 offsets
->old
, commit_count
,
1353 padding_size
, handle
);
1357 * lib_ring_buffer_switch_new_start: Populate new subbuffer.
1359 * This code can be executed unordered : writers may already have written to the
1360 * sub-buffer before this code gets executed, caution. The commit makes sure
1361 * that this code is executed before the deliver of this sub-buffer.
1364 void lib_ring_buffer_switch_new_start(struct lttng_ust_lib_ring_buffer
*buf
,
1365 struct channel
*chan
,
1366 struct switch_offsets
*offsets
,
1368 struct lttng_ust_shm_handle
*handle
)
1370 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1371 unsigned long beginidx
= subbuf_index(offsets
->begin
, chan
);
1372 unsigned long commit_count
;
1374 config
->cb
.buffer_begin(buf
, tsc
, beginidx
, handle
);
1377 * Order all writes to buffer before the commit count update that will
1378 * determine that the subbuffer is full.
1381 v_add(config
, config
->cb
.subbuffer_header_size(),
1382 &shmp_index(handle
, buf
->commit_hot
, beginidx
)->cc
);
1383 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, beginidx
)->cc
);
1384 /* Check if the written buffer has to be delivered */
1385 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->begin
,
1386 commit_count
, beginidx
, handle
);
1387 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, beginidx
,
1388 offsets
->begin
, commit_count
,
1389 config
->cb
.subbuffer_header_size(),
1394 * lib_ring_buffer_switch_new_end: finish switching current subbuffer
1396 * The only remaining threads could be the ones with pending commits. They will
1397 * have to do the deliver themselves.
1400 void lib_ring_buffer_switch_new_end(struct lttng_ust_lib_ring_buffer
*buf
,
1401 struct channel
*chan
,
1402 struct switch_offsets
*offsets
,
1404 struct lttng_ust_shm_handle
*handle
)
1406 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1407 unsigned long endidx
= subbuf_index(offsets
->end
- 1, chan
);
1408 unsigned long commit_count
, padding_size
, data_size
;
1410 data_size
= subbuf_offset(offsets
->end
- 1, chan
) + 1;
1411 padding_size
= chan
->backend
.subbuf_size
- data_size
;
1412 subbuffer_set_data_size(config
, &buf
->backend
, endidx
, data_size
,
1416 * Order all writes to buffer before the commit count update that will
1417 * determine that the subbuffer is full.
1420 v_add(config
, padding_size
, &shmp_index(handle
, buf
->commit_hot
, endidx
)->cc
);
1421 commit_count
= v_read(config
, &shmp_index(handle
, buf
->commit_hot
, endidx
)->cc
);
1422 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->end
- 1,
1423 commit_count
, endidx
, handle
);
1424 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, endidx
,
1425 offsets
->end
, commit_count
,
1426 padding_size
, handle
);
1432 * !0 if execution must be aborted.
1435 int lib_ring_buffer_try_switch_slow(enum switch_mode mode
,
1436 struct lttng_ust_lib_ring_buffer
*buf
,
1437 struct channel
*chan
,
1438 struct switch_offsets
*offsets
,
1441 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1444 offsets
->begin
= v_read(config
, &buf
->offset
);
1445 offsets
->old
= offsets
->begin
;
1446 offsets
->switch_old_start
= 0;
1447 off
= subbuf_offset(offsets
->begin
, chan
);
1449 *tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1452 * Ensure we flush the header of an empty subbuffer when doing the
1453 * finalize (SWITCH_FLUSH). This ensures that we end up knowing the
1454 * total data gathering duration even if there were no records saved
1455 * after the last buffer switch.
1456 * In SWITCH_ACTIVE mode, switch the buffer when it contains events.
1457 * SWITCH_ACTIVE only flushes the current subbuffer, dealing with end of
1458 * subbuffer header as appropriate.
1459 * The next record that reserves space will be responsible for
1460 * populating the following subbuffer header. We choose not to populate
1461 * the next subbuffer header here because we want to be able to use
1462 * SWITCH_ACTIVE for periodical buffer flush, which must
1463 * guarantee that all the buffer content (records and header
1464 * timestamps) are visible to the reader. This is required for
1465 * quiescence guarantees for the fusion merge.
1467 if (mode
== SWITCH_FLUSH
|| off
> 0) {
1468 if (caa_unlikely(off
== 0)) {
1470 * A final flush that encounters an empty
1471 * sub-buffer cannot switch buffer if a
1472 * reader is located within this sub-buffer.
1473 * Anyway, the purpose of final flushing of a
1474 * sub-buffer at offset 0 is to handle the case
1475 * of entirely empty stream.
1477 if (caa_unlikely(subbuf_trunc(offsets
->begin
, chan
)
1478 - subbuf_trunc((unsigned long)
1479 uatomic_read(&buf
->consumed
), chan
)
1480 >= chan
->backend
.buf_size
))
1483 * The client does not save any header information.
1484 * Don't switch empty subbuffer on finalize, because it
1485 * is invalid to deliver a completely empty subbuffer.
1487 if (!config
->cb
.subbuffer_header_size())
1490 * Need to write the subbuffer start header on finalize.
1492 offsets
->switch_old_start
= 1;
1494 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1496 return -1; /* we do not have to switch : buffer is empty */
1497 /* Note: old points to the next subbuf at offset 0 */
1498 offsets
->end
= offsets
->begin
;
1503 * Force a sub-buffer switch. This operation is completely reentrant : can be
1504 * called while tracing is active with absolutely no lock held.
1506 * Note, however, that as a v_cmpxchg is used for some atomic
1507 * operations, this function must be called from the CPU which owns the buffer
1508 * for a ACTIVE flush.
1510 void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer
*buf
, enum switch_mode mode
,
1511 struct lttng_ust_shm_handle
*handle
)
1513 struct channel
*chan
= shmp(handle
, buf
->backend
.chan
);
1514 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1515 struct switch_offsets offsets
;
1516 unsigned long oldidx
;
1522 * Perform retryable operations.
1525 if (lib_ring_buffer_try_switch_slow(mode
, buf
, chan
, &offsets
,
1527 return; /* Switch not needed */
1528 } while (v_cmpxchg(config
, &buf
->offset
, offsets
.old
, offsets
.end
)
1532 * Atomically update last_tsc. This update races against concurrent
1533 * atomic updates, but the race will always cause supplementary full TSC
1534 * records, never the opposite (missing a full TSC record when it would
1537 save_last_tsc(config
, buf
, tsc
);
1540 * Push the reader if necessary
1542 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.old
);
1544 oldidx
= subbuf_index(offsets
.old
, chan
);
1545 lib_ring_buffer_clear_noref(config
, &buf
->backend
, oldidx
, handle
);
1548 * May need to populate header start on SWITCH_FLUSH.
1550 if (offsets
.switch_old_start
) {
1551 lib_ring_buffer_switch_old_start(buf
, chan
, &offsets
, tsc
, handle
);
1552 offsets
.old
+= config
->cb
.subbuffer_header_size();
1556 * Switch old subbuffer.
1558 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, tsc
, handle
);
1564 * -ENOSPC if event size is too large for packet.
1565 * -ENOBUFS if there is currently not enough space in buffer for the event.
1566 * -EIO if data cannot be written into the buffer for any other reason.
1569 int lib_ring_buffer_try_reserve_slow(struct lttng_ust_lib_ring_buffer
*buf
,
1570 struct channel
*chan
,
1571 struct switch_offsets
*offsets
,
1572 struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
1574 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1575 struct lttng_ust_shm_handle
*handle
= ctx
->handle
;
1576 unsigned long reserve_commit_diff
;
1578 offsets
->begin
= v_read(config
, &buf
->offset
);
1579 offsets
->old
= offsets
->begin
;
1580 offsets
->switch_new_start
= 0;
1581 offsets
->switch_new_end
= 0;
1582 offsets
->switch_old_end
= 0;
1583 offsets
->pre_header_padding
= 0;
1585 ctx
->tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1586 if ((int64_t) ctx
->tsc
== -EIO
)
1589 if (last_tsc_overflow(config
, buf
, ctx
->tsc
))
1590 ctx
->rflags
|= RING_BUFFER_RFLAG_FULL_TSC
;
1592 if (caa_unlikely(subbuf_offset(offsets
->begin
, ctx
->chan
) == 0)) {
1593 offsets
->switch_new_start
= 1; /* For offsets->begin */
1595 offsets
->size
= config
->cb
.record_header_size(config
, chan
,
1597 &offsets
->pre_header_padding
,
1600 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1603 if (caa_unlikely(subbuf_offset(offsets
->begin
, chan
) +
1604 offsets
->size
> chan
->backend
.subbuf_size
)) {
1605 offsets
->switch_old_end
= 1; /* For offsets->old */
1606 offsets
->switch_new_start
= 1; /* For offsets->begin */
1609 if (caa_unlikely(offsets
->switch_new_start
)) {
1610 unsigned long sb_index
;
1613 * We are typically not filling the previous buffer completely.
1615 if (caa_likely(offsets
->switch_old_end
))
1616 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1617 offsets
->begin
= offsets
->begin
1618 + config
->cb
.subbuffer_header_size();
1619 /* Test new buffer integrity */
1620 sb_index
= subbuf_index(offsets
->begin
, chan
);
1621 reserve_commit_diff
=
1622 (buf_trunc(offsets
->begin
, chan
)
1623 >> chan
->backend
.num_subbuf_order
)
1624 - ((unsigned long) v_read(config
,
1625 &shmp_index(handle
, buf
->commit_cold
, sb_index
)->cc_sb
)
1626 & chan
->commit_count_mask
);
1627 if (caa_likely(reserve_commit_diff
== 0)) {
1628 /* Next subbuffer not being written to. */
1629 if (caa_unlikely(config
->mode
!= RING_BUFFER_OVERWRITE
&&
1630 subbuf_trunc(offsets
->begin
, chan
)
1631 - subbuf_trunc((unsigned long)
1632 uatomic_read(&buf
->consumed
), chan
)
1633 >= chan
->backend
.buf_size
)) {
1634 unsigned long nr_lost
;
1637 * We do not overwrite non consumed buffers
1638 * and we are full : record is lost.
1640 nr_lost
= v_read(config
, &buf
->records_lost_full
);
1641 v_inc(config
, &buf
->records_lost_full
);
1642 if ((nr_lost
& (DBG_PRINT_NR_LOST
- 1)) == 0) {
1643 DBG("%lu or more records lost in (%s:%d) (buffer full)\n",
1644 nr_lost
+ 1, chan
->backend
.name
,
1650 * Next subbuffer not being written to, and we
1651 * are either in overwrite mode or the buffer is
1652 * not full. It's safe to write in this new
1657 unsigned long nr_lost
;
1660 * Next subbuffer reserve offset does not match the
1661 * commit offset. Drop record in producer-consumer and
1662 * overwrite mode. Caused by either a writer OOPS or too
1663 * many nested writes over a reserve/commit pair.
1665 nr_lost
= v_read(config
, &buf
->records_lost_wrap
);
1666 v_inc(config
, &buf
->records_lost_wrap
);
1667 if ((nr_lost
& (DBG_PRINT_NR_LOST
- 1)) == 0) {
1668 DBG("%lu or more records lost in (%s:%d) (wrap-around)\n",
1669 nr_lost
+ 1, chan
->backend
.name
,
1675 config
->cb
.record_header_size(config
, chan
,
1677 &offsets
->pre_header_padding
,
1680 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1683 if (caa_unlikely(subbuf_offset(offsets
->begin
, chan
)
1684 + offsets
->size
> chan
->backend
.subbuf_size
)) {
1685 unsigned long nr_lost
;
1688 * Record too big for subbuffers, report error, don't
1689 * complete the sub-buffer switch.
1691 nr_lost
= v_read(config
, &buf
->records_lost_big
);
1692 v_inc(config
, &buf
->records_lost_big
);
1693 if ((nr_lost
& (DBG_PRINT_NR_LOST
- 1)) == 0) {
1694 DBG("%lu or more records lost in (%s:%d) record size "
1695 " of %zu bytes is too large for buffer\n",
1696 nr_lost
+ 1, chan
->backend
.name
,
1697 buf
->backend
.cpu
, offsets
->size
);
1702 * We just made a successful buffer switch and the
1703 * record fits in the new subbuffer. Let's write.
1708 * Record fits in the current buffer and we are not on a switch
1709 * boundary. It's safe to write.
1712 offsets
->end
= offsets
->begin
+ offsets
->size
;
1714 if (caa_unlikely(subbuf_offset(offsets
->end
, chan
) == 0)) {
1716 * The offset_end will fall at the very beginning of the next
1719 offsets
->switch_new_end
= 1; /* For offsets->begin */
1725 * lib_ring_buffer_reserve_slow - Atomic slot reservation in a buffer.
1726 * @ctx: ring buffer context.
1728 * Return : -NOBUFS if not enough space, -ENOSPC if event size too large,
1729 * -EIO for other errors, else returns 0.
1730 * It will take care of sub-buffer switching.
1732 int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx
*ctx
)
1734 struct channel
*chan
= ctx
->chan
;
1735 struct lttng_ust_shm_handle
*handle
= ctx
->handle
;
1736 const struct lttng_ust_lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1737 struct lttng_ust_lib_ring_buffer
*buf
;
1738 struct switch_offsets offsets
;
1741 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
1742 buf
= shmp(handle
, chan
->backend
.buf
[ctx
->cpu
].shmp
);
1744 buf
= shmp(handle
, chan
->backend
.buf
[0].shmp
);
1750 ret
= lib_ring_buffer_try_reserve_slow(buf
, chan
, &offsets
,
1752 if (caa_unlikely(ret
))
1754 } while (caa_unlikely(v_cmpxchg(config
, &buf
->offset
, offsets
.old
,
1759 * Atomically update last_tsc. This update races against concurrent
1760 * atomic updates, but the race will always cause supplementary full TSC
1761 * records, never the opposite (missing a full TSC record when it would
1764 save_last_tsc(config
, buf
, ctx
->tsc
);
1767 * Push the reader if necessary
1769 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.end
- 1);
1772 * Clear noref flag for this subbuffer.
1774 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
1775 subbuf_index(offsets
.end
- 1, chan
),
1779 * Switch old subbuffer if needed.
1781 if (caa_unlikely(offsets
.switch_old_end
)) {
1782 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
1783 subbuf_index(offsets
.old
- 1, chan
),
1785 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, ctx
->tsc
, handle
);
1789 * Populate new subbuffer.
1791 if (caa_unlikely(offsets
.switch_new_start
))
1792 lib_ring_buffer_switch_new_start(buf
, chan
, &offsets
, ctx
->tsc
, handle
);
1794 if (caa_unlikely(offsets
.switch_new_end
))
1795 lib_ring_buffer_switch_new_end(buf
, chan
, &offsets
, ctx
->tsc
, handle
);
1797 ctx
->slot_size
= offsets
.size
;
1798 ctx
->pre_offset
= offsets
.begin
;
1799 ctx
->buf_offset
= offsets
.begin
+ offsets
.pre_header_padding
;
1804 * Force a read (imply TLS fixup for dlopen) of TLS variables.
1806 void lttng_fixup_ringbuffer_tls(void)
1808 asm volatile ("" : : "m" (URCU_TLS(lib_ring_buffer_nesting
)));
1811 void lib_ringbuffer_signal_init(void)
1817 * Block signal for entire process, so only our thread processes
1821 ret
= pthread_sigmask(SIG_BLOCK
, &mask
, NULL
);
1824 PERROR("pthread_sigmask");