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
54 #include <linux/delay.h>
55 #include <linux/module.h>
56 #include <linux/percpu.h>
58 #include <wrapper/ringbuffer/config.h>
59 #include <wrapper/ringbuffer/backend.h>
60 #include <wrapper/ringbuffer/frontend.h>
61 #include <wrapper/ringbuffer/iterator.h>
62 #include <wrapper/ringbuffer/nohz.h>
63 #include <wrapper/atomic.h>
64 #include <wrapper/kref.h>
65 #include <wrapper/percpu-defs.h>
66 #include <wrapper/timer.h>
69 * Internal structure representing offsets to use at a sub-buffer switch.
71 struct switch_offsets
{
72 unsigned long begin
, end
, old
;
73 size_t pre_header_padding
, size
;
74 unsigned int switch_new_start
:1, switch_new_end
:1, switch_old_start
:1,
85 static ATOMIC_NOTIFIER_HEAD(tick_nohz_notifier
);
86 #endif /* CONFIG_NO_HZ */
88 static DEFINE_PER_CPU(spinlock_t
, ring_buffer_nohz_lock
);
90 DEFINE_PER_CPU(unsigned int, lib_ring_buffer_nesting
);
91 EXPORT_PER_CPU_SYMBOL(lib_ring_buffer_nesting
);
94 void lib_ring_buffer_print_errors(struct channel
*chan
,
95 struct lib_ring_buffer
*buf
, int cpu
);
97 void _lib_ring_buffer_switch_remote(struct lib_ring_buffer
*buf
,
98 enum switch_mode mode
);
101 int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config
*config
,
102 struct lib_ring_buffer
*buf
,
103 struct channel
*chan
)
105 unsigned long consumed_old
, consumed_idx
, commit_count
, write_offset
;
107 consumed_old
= atomic_long_read(&buf
->consumed
);
108 consumed_idx
= subbuf_index(consumed_old
, chan
);
109 commit_count
= v_read(config
, &buf
->commit_cold
[consumed_idx
].cc_sb
);
111 * No memory barrier here, since we are only interested
112 * in a statistically correct polling result. The next poll will
113 * get the data is we are racing. The mb() that ensures correct
114 * memory order is in get_subbuf.
116 write_offset
= v_read(config
, &buf
->offset
);
119 * Check that the subbuffer we are trying to consume has been
120 * already fully committed.
123 if (((commit_count
- chan
->backend
.subbuf_size
)
124 & chan
->commit_count_mask
)
125 - (buf_trunc(consumed_old
, chan
)
126 >> chan
->backend
.num_subbuf_order
)
131 * Check that we are not about to read the same subbuffer in
132 * which the writer head is.
134 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_old
, chan
)
142 * Must be called under cpu hotplug protection.
144 void lib_ring_buffer_free(struct lib_ring_buffer
*buf
)
146 struct channel
*chan
= buf
->backend
.chan
;
148 lib_ring_buffer_print_errors(chan
, buf
, buf
->backend
.cpu
);
149 kfree(buf
->commit_hot
);
150 kfree(buf
->commit_cold
);
152 lib_ring_buffer_backend_free(&buf
->backend
);
156 * lib_ring_buffer_reset - Reset ring buffer to initial values.
159 * Effectively empty the ring buffer. Should be called when the buffer is not
160 * used for writing. The ring buffer can be opened for reading, but the reader
161 * should not be using the iterator concurrently with reset. The previous
162 * current iterator record is reset.
164 void lib_ring_buffer_reset(struct lib_ring_buffer
*buf
)
166 struct channel
*chan
= buf
->backend
.chan
;
167 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
171 * Reset iterator first. It will put the subbuffer if it currently holds
174 lib_ring_buffer_iterator_reset(buf
);
175 v_set(config
, &buf
->offset
, 0);
176 for (i
= 0; i
< chan
->backend
.num_subbuf
; i
++) {
177 v_set(config
, &buf
->commit_hot
[i
].cc
, 0);
178 v_set(config
, &buf
->commit_hot
[i
].seq
, 0);
179 v_set(config
, &buf
->commit_cold
[i
].cc_sb
, 0);
181 atomic_long_set(&buf
->consumed
, 0);
182 atomic_set(&buf
->record_disabled
, 0);
183 v_set(config
, &buf
->last_tsc
, 0);
184 lib_ring_buffer_backend_reset(&buf
->backend
);
185 /* Don't reset number of active readers */
186 v_set(config
, &buf
->records_lost_full
, 0);
187 v_set(config
, &buf
->records_lost_wrap
, 0);
188 v_set(config
, &buf
->records_lost_big
, 0);
189 v_set(config
, &buf
->records_count
, 0);
190 v_set(config
, &buf
->records_overrun
, 0);
193 EXPORT_SYMBOL_GPL(lib_ring_buffer_reset
);
196 * channel_reset - Reset channel to initial values.
199 * Effectively empty the channel. Should be called when the channel is not used
200 * for writing. The channel can be opened for reading, but the reader should not
201 * be using the iterator concurrently with reset. The previous current iterator
204 void channel_reset(struct channel
*chan
)
207 * Reset iterators first. Will put the subbuffer if held for reading.
209 channel_iterator_reset(chan
);
210 atomic_set(&chan
->record_disabled
, 0);
211 /* Don't reset commit_count_mask, still valid */
212 channel_backend_reset(&chan
->backend
);
213 /* Don't reset switch/read timer interval */
214 /* Don't reset notifiers and notifier enable bits */
215 /* Don't reset reader reference count */
217 EXPORT_SYMBOL_GPL(channel_reset
);
220 * Must be called under cpu hotplug protection.
222 int lib_ring_buffer_create(struct lib_ring_buffer
*buf
,
223 struct channel_backend
*chanb
, int cpu
)
225 const struct lib_ring_buffer_config
*config
= &chanb
->config
;
226 struct channel
*chan
= container_of(chanb
, struct channel
, backend
);
227 void *priv
= chanb
->priv
;
228 size_t subbuf_header_size
;
232 /* Test for cpu hotplug */
233 if (buf
->backend
.allocated
)
237 * Paranoia: per cpu dynamic allocation is not officially documented as
238 * zeroing the memory, so let's do it here too, just in case.
240 memset(buf
, 0, sizeof(*buf
));
242 ret
= lib_ring_buffer_backend_create(&buf
->backend
, &chan
->backend
, cpu
);
247 kzalloc_node(ALIGN(sizeof(*buf
->commit_hot
)
248 * chan
->backend
.num_subbuf
,
249 1 << INTERNODE_CACHE_SHIFT
),
250 GFP_KERNEL
| __GFP_NOWARN
,
251 cpu_to_node(max(cpu
, 0)));
252 if (!buf
->commit_hot
) {
258 kzalloc_node(ALIGN(sizeof(*buf
->commit_cold
)
259 * chan
->backend
.num_subbuf
,
260 1 << INTERNODE_CACHE_SHIFT
),
261 GFP_KERNEL
| __GFP_NOWARN
,
262 cpu_to_node(max(cpu
, 0)));
263 if (!buf
->commit_cold
) {
268 init_waitqueue_head(&buf
->read_wait
);
269 init_waitqueue_head(&buf
->write_wait
);
270 raw_spin_lock_init(&buf
->raw_tick_nohz_spinlock
);
273 * Write the subbuffer header for first subbuffer so we know the total
274 * duration of data gathering.
276 subbuf_header_size
= config
->cb
.subbuffer_header_size();
277 v_set(config
, &buf
->offset
, subbuf_header_size
);
278 subbuffer_id_clear_noref(config
, &buf
->backend
.buf_wsb
[0].id
);
279 tsc
= config
->cb
.ring_buffer_clock_read(buf
->backend
.chan
);
280 config
->cb
.buffer_begin(buf
, tsc
, 0);
281 v_add(config
, subbuf_header_size
, &buf
->commit_hot
[0].cc
);
283 if (config
->cb
.buffer_create
) {
284 ret
= config
->cb
.buffer_create(buf
, priv
, cpu
, chanb
->name
);
290 * Ensure the buffer is ready before setting it to allocated and setting
292 * Used for cpu hotplug vs cpumask iteration.
295 buf
->backend
.allocated
= 1;
297 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
298 CHAN_WARN_ON(chan
, cpumask_test_cpu(cpu
,
299 chan
->backend
.cpumask
));
300 cpumask_set_cpu(cpu
, chan
->backend
.cpumask
);
307 kfree(buf
->commit_cold
);
309 kfree(buf
->commit_hot
);
311 lib_ring_buffer_backend_free(&buf
->backend
);
315 static void switch_buffer_timer(unsigned long data
)
317 struct lib_ring_buffer
*buf
= (struct lib_ring_buffer
*)data
;
318 struct channel
*chan
= buf
->backend
.chan
;
319 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
322 * Only flush buffers periodically if readers are active.
324 if (atomic_long_read(&buf
->active_readers
))
325 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
327 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
328 lttng_mod_timer_pinned(&buf
->switch_timer
,
329 jiffies
+ chan
->switch_timer_interval
);
331 mod_timer(&buf
->switch_timer
,
332 jiffies
+ chan
->switch_timer_interval
);
336 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
338 static void lib_ring_buffer_start_switch_timer(struct lib_ring_buffer
*buf
)
340 struct channel
*chan
= buf
->backend
.chan
;
341 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
343 if (!chan
->switch_timer_interval
|| buf
->switch_timer_enabled
)
346 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
347 lttng_init_timer_pinned(&buf
->switch_timer
);
349 init_timer(&buf
->switch_timer
);
351 buf
->switch_timer
.function
= switch_buffer_timer
;
352 buf
->switch_timer
.expires
= jiffies
+ chan
->switch_timer_interval
;
353 buf
->switch_timer
.data
= (unsigned long)buf
;
354 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
355 add_timer_on(&buf
->switch_timer
, buf
->backend
.cpu
);
357 add_timer(&buf
->switch_timer
);
358 buf
->switch_timer_enabled
= 1;
362 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
364 static void lib_ring_buffer_stop_switch_timer(struct lib_ring_buffer
*buf
)
366 struct channel
*chan
= buf
->backend
.chan
;
368 if (!chan
->switch_timer_interval
|| !buf
->switch_timer_enabled
)
371 del_timer_sync(&buf
->switch_timer
);
372 buf
->switch_timer_enabled
= 0;
376 * Polling timer to check the channels for data.
378 static void read_buffer_timer(unsigned long data
)
380 struct lib_ring_buffer
*buf
= (struct lib_ring_buffer
*)data
;
381 struct channel
*chan
= buf
->backend
.chan
;
382 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
384 CHAN_WARN_ON(chan
, !buf
->backend
.allocated
);
386 if (atomic_long_read(&buf
->active_readers
)
387 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
388 wake_up_interruptible(&buf
->read_wait
);
389 wake_up_interruptible(&chan
->read_wait
);
392 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
393 lttng_mod_timer_pinned(&buf
->read_timer
,
394 jiffies
+ chan
->read_timer_interval
);
396 mod_timer(&buf
->read_timer
,
397 jiffies
+ chan
->read_timer_interval
);
401 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
403 static void lib_ring_buffer_start_read_timer(struct lib_ring_buffer
*buf
)
405 struct channel
*chan
= buf
->backend
.chan
;
406 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
408 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
409 || !chan
->read_timer_interval
410 || buf
->read_timer_enabled
)
413 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
414 lttng_init_timer_pinned(&buf
->read_timer
);
416 init_timer(&buf
->read_timer
);
418 buf
->read_timer
.function
= read_buffer_timer
;
419 buf
->read_timer
.expires
= jiffies
+ chan
->read_timer_interval
;
420 buf
->read_timer
.data
= (unsigned long)buf
;
422 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
423 add_timer_on(&buf
->read_timer
, buf
->backend
.cpu
);
425 add_timer(&buf
->read_timer
);
426 buf
->read_timer_enabled
= 1;
430 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
432 static void lib_ring_buffer_stop_read_timer(struct lib_ring_buffer
*buf
)
434 struct channel
*chan
= buf
->backend
.chan
;
435 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
437 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
438 || !chan
->read_timer_interval
439 || !buf
->read_timer_enabled
)
442 del_timer_sync(&buf
->read_timer
);
444 * do one more check to catch data that has been written in the last
447 if (lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
448 wake_up_interruptible(&buf
->read_wait
);
449 wake_up_interruptible(&chan
->read_wait
);
451 buf
->read_timer_enabled
= 0;
454 #ifdef CONFIG_HOTPLUG_CPU
456 * lib_ring_buffer_cpu_hp_callback - CPU hotplug callback
457 * @nb: notifier block
458 * @action: hotplug action to take
461 * Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
464 int lib_ring_buffer_cpu_hp_callback(struct notifier_block
*nb
,
465 unsigned long action
,
468 unsigned int cpu
= (unsigned long)hcpu
;
469 struct channel
*chan
= container_of(nb
, struct channel
,
471 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
, cpu
);
472 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
474 if (!chan
->cpu_hp_enable
)
477 CHAN_WARN_ON(chan
, config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
);
480 case CPU_DOWN_FAILED
:
481 case CPU_DOWN_FAILED_FROZEN
:
483 case CPU_ONLINE_FROZEN
:
484 wake_up_interruptible(&chan
->hp_wait
);
485 lib_ring_buffer_start_switch_timer(buf
);
486 lib_ring_buffer_start_read_timer(buf
);
489 case CPU_DOWN_PREPARE
:
490 case CPU_DOWN_PREPARE_FROZEN
:
491 lib_ring_buffer_stop_switch_timer(buf
);
492 lib_ring_buffer_stop_read_timer(buf
);
496 case CPU_DEAD_FROZEN
:
498 * Performing a buffer switch on a remote CPU. Performed by
499 * the CPU responsible for doing the hotunplug after the target
500 * CPU stopped running completely. Ensures that all data
501 * from that remote CPU is flushed.
503 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
512 #if defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER)
514 * For per-cpu buffers, call the reader wakeups before switching the buffer, so
515 * that wake-up-tracing generated events are flushed before going idle (in
516 * tick_nohz). We test if the spinlock is locked to deal with the race where
517 * readers try to sample the ring buffer before we perform the switch. We let
518 * the readers retry in that case. If there is data in the buffer, the wake up
519 * is going to forbid the CPU running the reader thread from going idle.
521 static int notrace
ring_buffer_tick_nohz_callback(struct notifier_block
*nb
,
525 struct channel
*chan
= container_of(nb
, struct channel
,
527 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
528 struct lib_ring_buffer
*buf
;
529 int cpu
= smp_processor_id();
531 if (config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
) {
533 * We don't support keeping the system idle with global buffers
534 * and streaming active. In order to do so, we would need to
535 * sample a non-nohz-cpumask racelessly with the nohz updates
536 * without adding synchronization overhead to nohz. Leave this
537 * use-case out for now.
542 buf
= channel_get_ring_buffer(config
, chan
, cpu
);
544 case TICK_NOHZ_FLUSH
:
545 raw_spin_lock(&buf
->raw_tick_nohz_spinlock
);
546 if (config
->wakeup
== RING_BUFFER_WAKEUP_BY_TIMER
547 && chan
->read_timer_interval
548 && atomic_long_read(&buf
->active_readers
)
549 && (lib_ring_buffer_poll_deliver(config
, buf
, chan
)
550 || lib_ring_buffer_pending_data(config
, buf
, chan
))) {
551 wake_up_interruptible(&buf
->read_wait
);
552 wake_up_interruptible(&chan
->read_wait
);
554 if (chan
->switch_timer_interval
)
555 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
556 raw_spin_unlock(&buf
->raw_tick_nohz_spinlock
);
559 spin_lock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
560 lib_ring_buffer_stop_switch_timer(buf
);
561 lib_ring_buffer_stop_read_timer(buf
);
562 spin_unlock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
564 case TICK_NOHZ_RESTART
:
565 spin_lock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
566 lib_ring_buffer_start_read_timer(buf
);
567 lib_ring_buffer_start_switch_timer(buf
);
568 spin_unlock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
575 void notrace
lib_ring_buffer_tick_nohz_flush(void)
577 atomic_notifier_call_chain(&tick_nohz_notifier
, TICK_NOHZ_FLUSH
,
581 void notrace
lib_ring_buffer_tick_nohz_stop(void)
583 atomic_notifier_call_chain(&tick_nohz_notifier
, TICK_NOHZ_STOP
,
587 void notrace
lib_ring_buffer_tick_nohz_restart(void)
589 atomic_notifier_call_chain(&tick_nohz_notifier
, TICK_NOHZ_RESTART
,
592 #endif /* defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER) */
597 static void channel_unregister_notifiers(struct channel
*chan
)
599 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
602 channel_iterator_unregister_notifiers(chan
);
603 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
606 * Remove the nohz notifier first, so we are certain we stop
609 atomic_notifier_chain_unregister(&tick_nohz_notifier
,
610 &chan
->tick_nohz_notifier
);
612 * ring_buffer_nohz_lock will not be needed below, because
613 * we just removed the notifiers, which were the only source of
616 #endif /* CONFIG_NO_HZ */
617 #ifdef CONFIG_HOTPLUG_CPU
619 chan
->cpu_hp_enable
= 0;
620 for_each_online_cpu(cpu
) {
621 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
623 lib_ring_buffer_stop_switch_timer(buf
);
624 lib_ring_buffer_stop_read_timer(buf
);
627 unregister_cpu_notifier(&chan
->cpu_hp_notifier
);
629 for_each_possible_cpu(cpu
) {
630 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
632 lib_ring_buffer_stop_switch_timer(buf
);
633 lib_ring_buffer_stop_read_timer(buf
);
637 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
639 lib_ring_buffer_stop_switch_timer(buf
);
640 lib_ring_buffer_stop_read_timer(buf
);
642 channel_backend_unregister_notifiers(&chan
->backend
);
645 static void lib_ring_buffer_set_quiescent(struct lib_ring_buffer
*buf
)
647 if (!buf
->quiescent
) {
648 buf
->quiescent
= true;
649 _lib_ring_buffer_switch_remote(buf
, SWITCH_FLUSH
);
653 static void lib_ring_buffer_clear_quiescent(struct lib_ring_buffer
*buf
)
655 buf
->quiescent
= false;
658 void lib_ring_buffer_set_quiescent_channel(struct channel
*chan
)
661 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
663 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
665 for_each_channel_cpu(cpu
, chan
) {
666 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
669 lib_ring_buffer_set_quiescent(buf
);
673 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
675 lib_ring_buffer_set_quiescent(buf
);
678 EXPORT_SYMBOL_GPL(lib_ring_buffer_set_quiescent_channel
);
680 void lib_ring_buffer_clear_quiescent_channel(struct channel
*chan
)
683 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
685 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
687 for_each_channel_cpu(cpu
, chan
) {
688 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
691 lib_ring_buffer_clear_quiescent(buf
);
695 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
697 lib_ring_buffer_clear_quiescent(buf
);
700 EXPORT_SYMBOL_GPL(lib_ring_buffer_clear_quiescent_channel
);
702 static void channel_free(struct channel
*chan
)
704 if (chan
->backend
.release_priv_ops
) {
705 chan
->backend
.release_priv_ops(chan
->backend
.priv_ops
);
707 channel_iterator_free(chan
);
708 channel_backend_free(&chan
->backend
);
713 * channel_create - Create channel.
714 * @config: ring buffer instance configuration
715 * @name: name of the channel
716 * @priv: ring buffer client private data
717 * @buf_addr: pointer the the beginning of the preallocated buffer contiguous
718 * address mapping. It is used only by RING_BUFFER_STATIC
719 * configuration. It can be set to NULL for other backends.
720 * @subbuf_size: subbuffer size
721 * @num_subbuf: number of subbuffers
722 * @switch_timer_interval: Time interval (in us) to fill sub-buffers with
723 * padding to let readers get those sub-buffers.
724 * Used for live streaming.
725 * @read_timer_interval: Time interval (in us) to wake up pending readers.
728 * Returns NULL on failure.
730 struct channel
*channel_create(const struct lib_ring_buffer_config
*config
,
731 const char *name
, void *priv
, void *buf_addr
,
733 size_t num_subbuf
, unsigned int switch_timer_interval
,
734 unsigned int read_timer_interval
)
737 struct channel
*chan
;
739 if (lib_ring_buffer_check_config(config
, switch_timer_interval
,
740 read_timer_interval
))
743 chan
= kzalloc(sizeof(struct channel
), GFP_KERNEL
);
747 ret
= channel_backend_init(&chan
->backend
, name
, config
, priv
,
748 subbuf_size
, num_subbuf
);
752 ret
= channel_iterator_init(chan
);
754 goto error_free_backend
;
756 chan
->commit_count_mask
= (~0UL >> chan
->backend
.num_subbuf_order
);
757 chan
->switch_timer_interval
= usecs_to_jiffies(switch_timer_interval
);
758 chan
->read_timer_interval
= usecs_to_jiffies(read_timer_interval
);
759 kref_init(&chan
->ref
);
760 init_waitqueue_head(&chan
->read_wait
);
761 init_waitqueue_head(&chan
->hp_wait
);
763 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
764 #if defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER)
765 /* Only benefit from NO_HZ idle with per-cpu buffers for now. */
766 chan
->tick_nohz_notifier
.notifier_call
=
767 ring_buffer_tick_nohz_callback
;
768 chan
->tick_nohz_notifier
.priority
= ~0U;
769 atomic_notifier_chain_register(&tick_nohz_notifier
,
770 &chan
->tick_nohz_notifier
);
771 #endif /* defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER) */
774 * In case of non-hotplug cpu, if the ring-buffer is allocated
775 * in early initcall, it will not be notified of secondary cpus.
776 * In that off case, we need to allocate for all possible cpus.
778 #ifdef CONFIG_HOTPLUG_CPU
779 chan
->cpu_hp_notifier
.notifier_call
=
780 lib_ring_buffer_cpu_hp_callback
;
781 chan
->cpu_hp_notifier
.priority
= 6;
782 register_cpu_notifier(&chan
->cpu_hp_notifier
);
785 for_each_online_cpu(cpu
) {
786 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
788 spin_lock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
789 lib_ring_buffer_start_switch_timer(buf
);
790 lib_ring_buffer_start_read_timer(buf
);
791 spin_unlock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
793 chan
->cpu_hp_enable
= 1;
796 for_each_possible_cpu(cpu
) {
797 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
799 spin_lock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
800 lib_ring_buffer_start_switch_timer(buf
);
801 lib_ring_buffer_start_read_timer(buf
);
802 spin_unlock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
806 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
808 lib_ring_buffer_start_switch_timer(buf
);
809 lib_ring_buffer_start_read_timer(buf
);
815 channel_backend_free(&chan
->backend
);
820 EXPORT_SYMBOL_GPL(channel_create
);
823 void channel_release(struct kref
*kref
)
825 struct channel
*chan
= container_of(kref
, struct channel
, ref
);
830 * channel_destroy - Finalize, wait for q.s. and destroy channel.
831 * @chan: channel to destroy
834 * Call "destroy" callback, finalize channels, and then decrement the
835 * channel reference count. Note that when readers have completed data
836 * consumption of finalized channels, get_subbuf() will return -ENODATA.
837 * They should release their handle at that point. Returns the private
840 void *channel_destroy(struct channel
*chan
)
843 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
846 channel_unregister_notifiers(chan
);
848 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
850 * No need to hold cpu hotplug, because all notifiers have been
853 for_each_channel_cpu(cpu
, chan
) {
854 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
857 if (config
->cb
.buffer_finalize
)
858 config
->cb
.buffer_finalize(buf
,
861 if (buf
->backend
.allocated
)
862 lib_ring_buffer_set_quiescent(buf
);
864 * Perform flush before writing to finalized.
867 ACCESS_ONCE(buf
->finalized
) = 1;
868 wake_up_interruptible(&buf
->read_wait
);
871 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
873 if (config
->cb
.buffer_finalize
)
874 config
->cb
.buffer_finalize(buf
, chan
->backend
.priv
, -1);
875 if (buf
->backend
.allocated
)
876 lib_ring_buffer_set_quiescent(buf
);
878 * Perform flush before writing to finalized.
881 ACCESS_ONCE(buf
->finalized
) = 1;
882 wake_up_interruptible(&buf
->read_wait
);
884 ACCESS_ONCE(chan
->finalized
) = 1;
885 wake_up_interruptible(&chan
->hp_wait
);
886 wake_up_interruptible(&chan
->read_wait
);
887 priv
= chan
->backend
.priv
;
888 kref_put(&chan
->ref
, channel_release
);
891 EXPORT_SYMBOL_GPL(channel_destroy
);
893 struct lib_ring_buffer
*channel_get_ring_buffer(
894 const struct lib_ring_buffer_config
*config
,
895 struct channel
*chan
, int cpu
)
897 if (config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
)
898 return chan
->backend
.buf
;
900 return per_cpu_ptr(chan
->backend
.buf
, cpu
);
902 EXPORT_SYMBOL_GPL(channel_get_ring_buffer
);
904 int lib_ring_buffer_open_read(struct lib_ring_buffer
*buf
)
906 struct channel
*chan
= buf
->backend
.chan
;
908 if (!atomic_long_add_unless(&buf
->active_readers
, 1, 1))
910 if (!lttng_kref_get(&chan
->ref
)) {
911 atomic_long_dec(&buf
->active_readers
);
914 lttng_smp_mb__after_atomic();
917 EXPORT_SYMBOL_GPL(lib_ring_buffer_open_read
);
919 void lib_ring_buffer_release_read(struct lib_ring_buffer
*buf
)
921 struct channel
*chan
= buf
->backend
.chan
;
923 CHAN_WARN_ON(chan
, atomic_long_read(&buf
->active_readers
) != 1);
924 lttng_smp_mb__before_atomic();
925 atomic_long_dec(&buf
->active_readers
);
926 kref_put(&chan
->ref
, channel_release
);
928 EXPORT_SYMBOL_GPL(lib_ring_buffer_release_read
);
931 * Promote compiler barrier to a smp_mb().
932 * For the specific ring buffer case, this IPI call should be removed if the
933 * architecture does not reorder writes. This should eventually be provided by
934 * a separate architecture-specific infrastructure.
936 static void remote_mb(void *info
)
942 * lib_ring_buffer_snapshot - save subbuffer position snapshot (for read)
944 * @consumed: consumed count indicating the position where to read
945 * @produced: produced count, indicates position when to stop reading
947 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
948 * data to read at consumed position, or 0 if the get operation succeeds.
949 * Busy-loop trying to get data if the tick_nohz sequence lock is held.
952 int lib_ring_buffer_snapshot(struct lib_ring_buffer
*buf
,
953 unsigned long *consumed
, unsigned long *produced
)
955 struct channel
*chan
= buf
->backend
.chan
;
956 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
957 unsigned long consumed_cur
, write_offset
;
961 finalized
= ACCESS_ONCE(buf
->finalized
);
963 * Read finalized before counters.
966 consumed_cur
= atomic_long_read(&buf
->consumed
);
968 * No need to issue a memory barrier between consumed count read and
969 * write offset read, because consumed count can only change
970 * concurrently in overwrite mode, and we keep a sequence counter
971 * identifier derived from the write offset to check we are getting
972 * the same sub-buffer we are expecting (the sub-buffers are atomically
973 * "tagged" upon writes, tags are checked upon read).
975 write_offset
= v_read(config
, &buf
->offset
);
978 * Check that we are not about to read the same subbuffer in
979 * which the writer head is.
981 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_cur
, chan
)
985 *consumed
= consumed_cur
;
986 *produced
= subbuf_trunc(write_offset
, chan
);
992 * The memory barriers __wait_event()/wake_up_interruptible() take care
993 * of "raw_spin_is_locked" memory ordering.
997 else if (raw_spin_is_locked(&buf
->raw_tick_nohz_spinlock
))
1002 EXPORT_SYMBOL_GPL(lib_ring_buffer_snapshot
);
1005 * lib_ring_buffer_put_snapshot - move consumed counter forward
1007 * Should only be called from consumer context.
1009 * @consumed_new: new consumed count value
1011 void lib_ring_buffer_move_consumer(struct lib_ring_buffer
*buf
,
1012 unsigned long consumed_new
)
1014 struct lib_ring_buffer_backend
*bufb
= &buf
->backend
;
1015 struct channel
*chan
= bufb
->chan
;
1016 unsigned long consumed
;
1018 CHAN_WARN_ON(chan
, atomic_long_read(&buf
->active_readers
) != 1);
1021 * Only push the consumed value forward.
1022 * If the consumed cmpxchg fails, this is because we have been pushed by
1023 * the writer in flight recorder mode.
1025 consumed
= atomic_long_read(&buf
->consumed
);
1026 while ((long) consumed
- (long) consumed_new
< 0)
1027 consumed
= atomic_long_cmpxchg(&buf
->consumed
, consumed
,
1029 /* Wake-up the metadata producer */
1030 wake_up_interruptible(&buf
->write_wait
);
1032 EXPORT_SYMBOL_GPL(lib_ring_buffer_move_consumer
);
1035 * lib_ring_buffer_get_subbuf - get exclusive access to subbuffer for reading
1037 * @consumed: consumed count indicating the position where to read
1039 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
1040 * data to read at consumed position, or 0 if the get operation succeeds.
1041 * Busy-loop trying to get data if the tick_nohz sequence lock is held.
1043 int lib_ring_buffer_get_subbuf(struct lib_ring_buffer
*buf
,
1044 unsigned long consumed
)
1046 struct channel
*chan
= buf
->backend
.chan
;
1047 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1048 unsigned long consumed_cur
, consumed_idx
, commit_count
, write_offset
;
1052 if (buf
->get_subbuf
) {
1054 * Reader is trying to get a subbuffer twice.
1056 CHAN_WARN_ON(chan
, 1);
1060 finalized
= ACCESS_ONCE(buf
->finalized
);
1062 * Read finalized before counters.
1065 consumed_cur
= atomic_long_read(&buf
->consumed
);
1066 consumed_idx
= subbuf_index(consumed
, chan
);
1067 commit_count
= v_read(config
, &buf
->commit_cold
[consumed_idx
].cc_sb
);
1069 * Make sure we read the commit count before reading the buffer
1070 * data and the write offset. Correct consumed offset ordering
1071 * wrt commit count is insured by the use of cmpxchg to update
1072 * the consumed offset.
1073 * smp_call_function_single can fail if the remote CPU is offline,
1074 * this is OK because then there is no wmb to execute there.
1075 * If our thread is executing on the same CPU as the on the buffers
1076 * belongs to, we don't have to synchronize it at all. If we are
1077 * migrated, the scheduler will take care of the memory barriers.
1078 * Normally, smp_call_function_single() should ensure program order when
1079 * executing the remote function, which implies that it surrounds the
1080 * function execution with :
1091 * However, smp_call_function_single() does not seem to clearly execute
1092 * such barriers. It depends on spinlock semantic to provide the barrier
1093 * before executing the IPI and, when busy-looping, csd_lock_wait only
1094 * executes smp_mb() when it has to wait for the other CPU.
1096 * I don't trust this code. Therefore, let's add the smp_mb() sequence
1097 * required ourself, even if duplicated. It has no performance impact
1100 * smp_mb() is needed because smp_rmb() and smp_wmb() only order read vs
1101 * read and write vs write. They do not ensure core synchronization. We
1102 * really have to ensure total order between the 3 barriers running on
1105 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1106 if (config
->sync
== RING_BUFFER_SYNC_PER_CPU
1107 && config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
1108 if (raw_smp_processor_id() != buf
->backend
.cpu
) {
1109 /* Total order with IPI handler smp_mb() */
1111 smp_call_function_single(buf
->backend
.cpu
,
1112 remote_mb
, NULL
, 1);
1113 /* Total order with IPI handler smp_mb() */
1117 /* Total order with IPI handler smp_mb() */
1119 smp_call_function(remote_mb
, NULL
, 1);
1120 /* Total order with IPI handler smp_mb() */
1125 * Local rmb to match the remote wmb to read the commit count
1126 * before the buffer data and the write offset.
1131 write_offset
= v_read(config
, &buf
->offset
);
1134 * Check that the buffer we are getting is after or at consumed_cur
1137 if ((long) subbuf_trunc(consumed
, chan
)
1138 - (long) subbuf_trunc(consumed_cur
, chan
) < 0)
1142 * Check that the subbuffer we are trying to consume has been
1143 * already fully committed.
1145 if (((commit_count
- chan
->backend
.subbuf_size
)
1146 & chan
->commit_count_mask
)
1147 - (buf_trunc(consumed
, chan
)
1148 >> chan
->backend
.num_subbuf_order
)
1153 * Check that we are not about to read the same subbuffer in
1154 * which the writer head is.
1156 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed
, chan
)
1161 * Failure to get the subbuffer causes a busy-loop retry without going
1162 * to a wait queue. These are caused by short-lived race windows where
1163 * the writer is getting access to a subbuffer we were trying to get
1164 * access to. Also checks that the "consumed" buffer count we are
1165 * looking for matches the one contained in the subbuffer id.
1167 ret
= update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
1168 consumed_idx
, buf_trunc_val(consumed
, chan
));
1171 subbuffer_id_clear_noref(config
, &buf
->backend
.buf_rsb
.id
);
1173 buf
->get_subbuf_consumed
= consumed
;
1174 buf
->get_subbuf
= 1;
1180 * The memory barriers __wait_event()/wake_up_interruptible() take care
1181 * of "raw_spin_is_locked" memory ordering.
1185 else if (raw_spin_is_locked(&buf
->raw_tick_nohz_spinlock
))
1190 EXPORT_SYMBOL_GPL(lib_ring_buffer_get_subbuf
);
1193 * lib_ring_buffer_put_subbuf - release exclusive subbuffer access
1196 void lib_ring_buffer_put_subbuf(struct lib_ring_buffer
*buf
)
1198 struct lib_ring_buffer_backend
*bufb
= &buf
->backend
;
1199 struct channel
*chan
= bufb
->chan
;
1200 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1201 unsigned long read_sb_bindex
, consumed_idx
, consumed
;
1203 CHAN_WARN_ON(chan
, atomic_long_read(&buf
->active_readers
) != 1);
1205 if (!buf
->get_subbuf
) {
1207 * Reader puts a subbuffer it did not get.
1209 CHAN_WARN_ON(chan
, 1);
1212 consumed
= buf
->get_subbuf_consumed
;
1213 buf
->get_subbuf
= 0;
1216 * Clear the records_unread counter. (overruns counter)
1217 * Can still be non-zero if a file reader simply grabbed the data
1218 * without using iterators.
1219 * Can be below zero if an iterator is used on a snapshot more than
1222 read_sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
1223 v_add(config
, v_read(config
,
1224 &bufb
->array
[read_sb_bindex
]->records_unread
),
1225 &bufb
->records_read
);
1226 v_set(config
, &bufb
->array
[read_sb_bindex
]->records_unread
, 0);
1227 CHAN_WARN_ON(chan
, config
->mode
== RING_BUFFER_OVERWRITE
1228 && subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
1229 subbuffer_id_set_noref(config
, &bufb
->buf_rsb
.id
);
1232 * Exchange the reader subbuffer with the one we put in its place in the
1233 * writer subbuffer table. Expect the original consumed count. If
1234 * update_read_sb_index fails, this is because the writer updated the
1235 * subbuffer concurrently. We should therefore keep the subbuffer we
1236 * currently have: it has become invalid to try reading this sub-buffer
1237 * consumed count value anyway.
1239 consumed_idx
= subbuf_index(consumed
, chan
);
1240 update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
1241 consumed_idx
, buf_trunc_val(consumed
, chan
));
1243 * update_read_sb_index return value ignored. Don't exchange sub-buffer
1244 * if the writer concurrently updated it.
1247 EXPORT_SYMBOL_GPL(lib_ring_buffer_put_subbuf
);
1250 * cons_offset is an iterator on all subbuffer offsets between the reader
1251 * position and the writer position. (inclusive)
1254 void lib_ring_buffer_print_subbuffer_errors(struct lib_ring_buffer
*buf
,
1255 struct channel
*chan
,
1256 unsigned long cons_offset
,
1259 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1260 unsigned long cons_idx
, commit_count
, commit_count_sb
;
1262 cons_idx
= subbuf_index(cons_offset
, chan
);
1263 commit_count
= v_read(config
, &buf
->commit_hot
[cons_idx
].cc
);
1264 commit_count_sb
= v_read(config
, &buf
->commit_cold
[cons_idx
].cc_sb
);
1266 if (subbuf_offset(commit_count
, chan
) != 0)
1268 "ring buffer %s, cpu %d: "
1269 "commit count in subbuffer %lu,\n"
1270 "expecting multiples of %lu bytes\n"
1271 " [ %lu bytes committed, %lu bytes reader-visible ]\n",
1272 chan
->backend
.name
, cpu
, cons_idx
,
1273 chan
->backend
.subbuf_size
,
1274 commit_count
, commit_count_sb
);
1276 printk(KERN_DEBUG
"ring buffer: %s, cpu %d: %lu bytes committed\n",
1277 chan
->backend
.name
, cpu
, commit_count
);
1281 void lib_ring_buffer_print_buffer_errors(struct lib_ring_buffer
*buf
,
1282 struct channel
*chan
,
1283 void *priv
, int cpu
)
1285 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1286 unsigned long write_offset
, cons_offset
;
1289 * No need to order commit_count, write_offset and cons_offset reads
1290 * because we execute at teardown when no more writer nor reader
1291 * references are left.
1293 write_offset
= v_read(config
, &buf
->offset
);
1294 cons_offset
= atomic_long_read(&buf
->consumed
);
1295 if (write_offset
!= cons_offset
)
1297 "ring buffer %s, cpu %d: "
1298 "non-consumed data\n"
1299 " [ %lu bytes written, %lu bytes read ]\n",
1300 chan
->backend
.name
, cpu
, write_offset
, cons_offset
);
1302 for (cons_offset
= atomic_long_read(&buf
->consumed
);
1303 (long) (subbuf_trunc((unsigned long) v_read(config
, &buf
->offset
),
1306 cons_offset
= subbuf_align(cons_offset
, chan
))
1307 lib_ring_buffer_print_subbuffer_errors(buf
, chan
, cons_offset
,
1312 void lib_ring_buffer_print_errors(struct channel
*chan
,
1313 struct lib_ring_buffer
*buf
, int cpu
)
1315 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1316 void *priv
= chan
->backend
.priv
;
1318 if (!strcmp(chan
->backend
.name
, "relay-metadata")) {
1319 printk(KERN_DEBUG
"ring buffer %s: %lu records written, "
1320 "%lu records overrun\n",
1322 v_read(config
, &buf
->records_count
),
1323 v_read(config
, &buf
->records_overrun
));
1325 printk(KERN_DEBUG
"ring buffer %s, cpu %d: %lu records written, "
1326 "%lu records overrun\n",
1327 chan
->backend
.name
, cpu
,
1328 v_read(config
, &buf
->records_count
),
1329 v_read(config
, &buf
->records_overrun
));
1331 if (v_read(config
, &buf
->records_lost_full
)
1332 || v_read(config
, &buf
->records_lost_wrap
)
1333 || v_read(config
, &buf
->records_lost_big
))
1335 "ring buffer %s, cpu %d: records were lost. Caused by:\n"
1336 " [ %lu buffer full, %lu nest buffer wrap-around, "
1337 "%lu event too big ]\n",
1338 chan
->backend
.name
, cpu
,
1339 v_read(config
, &buf
->records_lost_full
),
1340 v_read(config
, &buf
->records_lost_wrap
),
1341 v_read(config
, &buf
->records_lost_big
));
1343 lib_ring_buffer_print_buffer_errors(buf
, chan
, priv
, cpu
);
1347 * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
1349 * Only executed by SWITCH_FLUSH, which can be issued while tracing is active
1350 * or at buffer finalization (destroy).
1353 void lib_ring_buffer_switch_old_start(struct lib_ring_buffer
*buf
,
1354 struct channel
*chan
,
1355 struct switch_offsets
*offsets
,
1358 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1359 unsigned long oldidx
= subbuf_index(offsets
->old
, chan
);
1360 unsigned long commit_count
;
1362 config
->cb
.buffer_begin(buf
, tsc
, oldidx
);
1365 * Order all writes to buffer before the commit count update that will
1366 * determine that the subbuffer is full.
1368 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1370 * Must write slot data before incrementing commit count. This
1371 * compiler barrier is upgraded into a smp_mb() by the IPI sent
1377 v_add(config
, config
->cb
.subbuffer_header_size(),
1378 &buf
->commit_hot
[oldidx
].cc
);
1379 commit_count
= v_read(config
, &buf
->commit_hot
[oldidx
].cc
);
1380 /* Check if the written buffer has to be delivered */
1381 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
,
1382 commit_count
, oldidx
, tsc
);
1383 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, oldidx
,
1384 offsets
->old
+ config
->cb
.subbuffer_header_size(),
1389 * lib_ring_buffer_switch_old_end: switch old subbuffer
1391 * Note : offset_old should never be 0 here. It is ok, because we never perform
1392 * buffer switch on an empty subbuffer in SWITCH_ACTIVE mode. The caller
1393 * increments the offset_old value when doing a SWITCH_FLUSH on an empty
1397 void lib_ring_buffer_switch_old_end(struct lib_ring_buffer
*buf
,
1398 struct channel
*chan
,
1399 struct switch_offsets
*offsets
,
1402 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1403 unsigned long oldidx
= subbuf_index(offsets
->old
- 1, chan
);
1404 unsigned long commit_count
, padding_size
, data_size
;
1406 data_size
= subbuf_offset(offsets
->old
- 1, chan
) + 1;
1407 padding_size
= chan
->backend
.subbuf_size
- data_size
;
1408 subbuffer_set_data_size(config
, &buf
->backend
, oldidx
, data_size
);
1411 * Order all writes to buffer before the commit count update that will
1412 * determine that the subbuffer is full.
1414 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1416 * Must write slot data before incrementing commit count. This
1417 * compiler barrier is upgraded into a smp_mb() by the IPI sent
1423 v_add(config
, padding_size
, &buf
->commit_hot
[oldidx
].cc
);
1424 commit_count
= v_read(config
, &buf
->commit_hot
[oldidx
].cc
);
1425 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
- 1,
1426 commit_count
, oldidx
, tsc
);
1427 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, oldidx
,
1428 offsets
->old
+ padding_size
, commit_count
);
1432 * lib_ring_buffer_switch_new_start: Populate new subbuffer.
1434 * This code can be executed unordered : writers may already have written to the
1435 * sub-buffer before this code gets executed, caution. The commit makes sure
1436 * that this code is executed before the deliver of this sub-buffer.
1439 void lib_ring_buffer_switch_new_start(struct lib_ring_buffer
*buf
,
1440 struct channel
*chan
,
1441 struct switch_offsets
*offsets
,
1444 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1445 unsigned long beginidx
= subbuf_index(offsets
->begin
, chan
);
1446 unsigned long commit_count
;
1448 config
->cb
.buffer_begin(buf
, tsc
, beginidx
);
1451 * Order all writes to buffer before the commit count update that will
1452 * determine that the subbuffer is full.
1454 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1456 * Must write slot data before incrementing commit count. This
1457 * compiler barrier is upgraded into a smp_mb() by the IPI sent
1463 v_add(config
, config
->cb
.subbuffer_header_size(),
1464 &buf
->commit_hot
[beginidx
].cc
);
1465 commit_count
= v_read(config
, &buf
->commit_hot
[beginidx
].cc
);
1466 /* Check if the written buffer has to be delivered */
1467 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->begin
,
1468 commit_count
, beginidx
, tsc
);
1469 lib_ring_buffer_write_commit_counter(config
, buf
, chan
, beginidx
,
1470 offsets
->begin
+ config
->cb
.subbuffer_header_size(),
1475 * lib_ring_buffer_switch_new_end: finish switching current subbuffer
1477 * Calls subbuffer_set_data_size() to set the data size of the current
1478 * sub-buffer. We do not need to perform check_deliver nor commit here,
1479 * since this task will be done by the "commit" of the event for which
1480 * we are currently doing the space reservation.
1483 void lib_ring_buffer_switch_new_end(struct lib_ring_buffer
*buf
,
1484 struct channel
*chan
,
1485 struct switch_offsets
*offsets
,
1488 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1489 unsigned long endidx
, data_size
;
1491 endidx
= subbuf_index(offsets
->end
- 1, chan
);
1492 data_size
= subbuf_offset(offsets
->end
- 1, chan
) + 1;
1493 subbuffer_set_data_size(config
, &buf
->backend
, endidx
, data_size
);
1499 * !0 if execution must be aborted.
1502 int lib_ring_buffer_try_switch_slow(enum switch_mode mode
,
1503 struct lib_ring_buffer
*buf
,
1504 struct channel
*chan
,
1505 struct switch_offsets
*offsets
,
1508 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1509 unsigned long off
, reserve_commit_diff
;
1511 offsets
->begin
= v_read(config
, &buf
->offset
);
1512 offsets
->old
= offsets
->begin
;
1513 offsets
->switch_old_start
= 0;
1514 off
= subbuf_offset(offsets
->begin
, chan
);
1516 *tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1519 * Ensure we flush the header of an empty subbuffer when doing the
1520 * finalize (SWITCH_FLUSH). This ensures that we end up knowing the
1521 * total data gathering duration even if there were no records saved
1522 * after the last buffer switch.
1523 * In SWITCH_ACTIVE mode, switch the buffer when it contains events.
1524 * SWITCH_ACTIVE only flushes the current subbuffer, dealing with end of
1525 * subbuffer header as appropriate.
1526 * The next record that reserves space will be responsible for
1527 * populating the following subbuffer header. We choose not to populate
1528 * the next subbuffer header here because we want to be able to use
1529 * SWITCH_ACTIVE for periodical buffer flush and CPU tick_nohz stop
1530 * buffer flush, which must guarantee that all the buffer content
1531 * (records and header timestamps) are visible to the reader. This is
1532 * required for quiescence guarantees for the fusion merge.
1534 if (mode
!= SWITCH_FLUSH
&& !off
)
1535 return -1; /* we do not have to switch : buffer is empty */
1537 if (unlikely(off
== 0)) {
1538 unsigned long sb_index
, commit_count
;
1541 * We are performing a SWITCH_FLUSH. There may be concurrent
1542 * writes into the buffer if e.g. invoked while performing a
1543 * snapshot on an active trace.
1545 * If the client does not save any header information (sub-buffer
1546 * header size == 0), don't switch empty subbuffer on finalize,
1547 * because it is invalid to deliver a completely empty
1550 if (!config
->cb
.subbuffer_header_size())
1553 /* Test new buffer integrity */
1554 sb_index
= subbuf_index(offsets
->begin
, chan
);
1555 commit_count
= v_read(config
,
1556 &buf
->commit_cold
[sb_index
].cc_sb
);
1557 reserve_commit_diff
=
1558 (buf_trunc(offsets
->begin
, chan
)
1559 >> chan
->backend
.num_subbuf_order
)
1560 - (commit_count
& chan
->commit_count_mask
);
1561 if (likely(reserve_commit_diff
== 0)) {
1562 /* Next subbuffer not being written to. */
1563 if (unlikely(config
->mode
!= RING_BUFFER_OVERWRITE
&&
1564 subbuf_trunc(offsets
->begin
, chan
)
1565 - subbuf_trunc((unsigned long)
1566 atomic_long_read(&buf
->consumed
), chan
)
1567 >= chan
->backend
.buf_size
)) {
1569 * We do not overwrite non consumed buffers
1570 * and we are full : don't switch.
1575 * Next subbuffer not being written to, and we
1576 * are either in overwrite mode or the buffer is
1577 * not full. It's safe to write in this new
1583 * Next subbuffer reserve offset does not match the
1584 * commit offset. Don't perform switch in
1585 * producer-consumer and overwrite mode. Caused by
1586 * either a writer OOPS or too many nested writes over a
1587 * reserve/commit pair.
1593 * Need to write the subbuffer start header on finalize.
1595 offsets
->switch_old_start
= 1;
1597 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1598 /* Note: old points to the next subbuf at offset 0 */
1599 offsets
->end
= offsets
->begin
;
1604 * Force a sub-buffer switch. This operation is completely reentrant : can be
1605 * called while tracing is active with absolutely no lock held.
1607 * Note, however, that as a v_cmpxchg is used for some atomic
1608 * operations, this function must be called from the CPU which owns the buffer
1609 * for a ACTIVE flush.
1611 void lib_ring_buffer_switch_slow(struct lib_ring_buffer
*buf
, enum switch_mode mode
)
1613 struct channel
*chan
= buf
->backend
.chan
;
1614 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1615 struct switch_offsets offsets
;
1616 unsigned long oldidx
;
1622 * Perform retryable operations.
1625 if (lib_ring_buffer_try_switch_slow(mode
, buf
, chan
, &offsets
,
1627 return; /* Switch not needed */
1628 } while (v_cmpxchg(config
, &buf
->offset
, offsets
.old
, offsets
.end
)
1632 * Atomically update last_tsc. This update races against concurrent
1633 * atomic updates, but the race will always cause supplementary full TSC
1634 * records, never the opposite (missing a full TSC record when it would
1637 save_last_tsc(config
, buf
, tsc
);
1640 * Push the reader if necessary
1642 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.old
);
1644 oldidx
= subbuf_index(offsets
.old
, chan
);
1645 lib_ring_buffer_clear_noref(config
, &buf
->backend
, oldidx
);
1648 * May need to populate header start on SWITCH_FLUSH.
1650 if (offsets
.switch_old_start
) {
1651 lib_ring_buffer_switch_old_start(buf
, chan
, &offsets
, tsc
);
1652 offsets
.old
+= config
->cb
.subbuffer_header_size();
1656 * Switch old subbuffer.
1658 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, tsc
);
1660 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow
);
1662 struct switch_param
{
1663 struct lib_ring_buffer
*buf
;
1664 enum switch_mode mode
;
1667 static void remote_switch(void *info
)
1669 struct switch_param
*param
= info
;
1670 struct lib_ring_buffer
*buf
= param
->buf
;
1672 lib_ring_buffer_switch_slow(buf
, param
->mode
);
1675 static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer
*buf
,
1676 enum switch_mode mode
)
1678 struct channel
*chan
= buf
->backend
.chan
;
1679 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1681 struct switch_param param
;
1684 * With global synchronization we don't need to use the IPI scheme.
1686 if (config
->sync
== RING_BUFFER_SYNC_GLOBAL
) {
1687 lib_ring_buffer_switch_slow(buf
, mode
);
1692 * Taking lock on CPU hotplug to ensure two things: first, that the
1693 * target cpu is not taken concurrently offline while we are within
1694 * smp_call_function_single() (I don't trust that get_cpu() on the
1695 * _local_ CPU actually inhibit CPU hotplug for the _remote_ CPU (to be
1696 * confirmed)). Secondly, if it happens that the CPU is not online, our
1697 * own call to lib_ring_buffer_switch_slow() needs to be protected from
1698 * CPU hotplug handlers, which can also perform a remote subbuffer
1704 ret
= smp_call_function_single(buf
->backend
.cpu
,
1705 remote_switch
, ¶m
, 1);
1707 /* Remote CPU is offline, do it ourself. */
1708 lib_ring_buffer_switch_slow(buf
, mode
);
1713 void lib_ring_buffer_switch_remote(struct lib_ring_buffer
*buf
)
1715 _lib_ring_buffer_switch_remote(buf
, SWITCH_ACTIVE
);
1717 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote
);
1719 /* Switch sub-buffer even if current sub-buffer is empty. */
1720 void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer
*buf
)
1722 _lib_ring_buffer_switch_remote(buf
, SWITCH_FLUSH
);
1724 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote_empty
);
1729 * -ENOSPC if event size is too large for packet.
1730 * -ENOBUFS if there is currently not enough space in buffer for the event.
1731 * -EIO if data cannot be written into the buffer for any other reason.
1734 int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer
*buf
,
1735 struct channel
*chan
,
1736 struct switch_offsets
*offsets
,
1737 struct lib_ring_buffer_ctx
*ctx
)
1739 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1740 unsigned long reserve_commit_diff
, offset_cmp
;
1743 offsets
->begin
= offset_cmp
= v_read(config
, &buf
->offset
);
1744 offsets
->old
= offsets
->begin
;
1745 offsets
->switch_new_start
= 0;
1746 offsets
->switch_new_end
= 0;
1747 offsets
->switch_old_end
= 0;
1748 offsets
->pre_header_padding
= 0;
1750 ctx
->tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1751 if ((int64_t) ctx
->tsc
== -EIO
)
1754 if (last_tsc_overflow(config
, buf
, ctx
->tsc
))
1755 ctx
->rflags
|= RING_BUFFER_RFLAG_FULL_TSC
;
1757 if (unlikely(subbuf_offset(offsets
->begin
, ctx
->chan
) == 0)) {
1758 offsets
->switch_new_start
= 1; /* For offsets->begin */
1760 offsets
->size
= config
->cb
.record_header_size(config
, chan
,
1762 &offsets
->pre_header_padding
,
1765 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1768 if (unlikely(subbuf_offset(offsets
->begin
, chan
) +
1769 offsets
->size
> chan
->backend
.subbuf_size
)) {
1770 offsets
->switch_old_end
= 1; /* For offsets->old */
1771 offsets
->switch_new_start
= 1; /* For offsets->begin */
1774 if (unlikely(offsets
->switch_new_start
)) {
1775 unsigned long sb_index
, commit_count
;
1778 * We are typically not filling the previous buffer completely.
1780 if (likely(offsets
->switch_old_end
))
1781 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1782 offsets
->begin
= offsets
->begin
1783 + config
->cb
.subbuffer_header_size();
1784 /* Test new buffer integrity */
1785 sb_index
= subbuf_index(offsets
->begin
, chan
);
1787 * Read buf->offset before buf->commit_cold[sb_index].cc_sb.
1788 * lib_ring_buffer_check_deliver() has the matching
1789 * memory barriers required around commit_cold cc_sb
1790 * updates to ensure reserve and commit counter updates
1791 * are not seen reordered when updated by another CPU.
1794 commit_count
= v_read(config
,
1795 &buf
->commit_cold
[sb_index
].cc_sb
);
1796 /* Read buf->commit_cold[sb_index].cc_sb before buf->offset. */
1798 if (unlikely(offset_cmp
!= v_read(config
, &buf
->offset
))) {
1800 * The reserve counter have been concurrently updated
1801 * while we read the commit counter. This means the
1802 * commit counter we read might not match buf->offset
1803 * due to concurrent update. We therefore need to retry.
1807 reserve_commit_diff
=
1808 (buf_trunc(offsets
->begin
, chan
)
1809 >> chan
->backend
.num_subbuf_order
)
1810 - (commit_count
& chan
->commit_count_mask
);
1811 if (likely(reserve_commit_diff
== 0)) {
1812 /* Next subbuffer not being written to. */
1813 if (unlikely(config
->mode
!= RING_BUFFER_OVERWRITE
&&
1814 subbuf_trunc(offsets
->begin
, chan
)
1815 - subbuf_trunc((unsigned long)
1816 atomic_long_read(&buf
->consumed
), chan
)
1817 >= chan
->backend
.buf_size
)) {
1819 * We do not overwrite non consumed buffers
1820 * and we are full : record is lost.
1822 v_inc(config
, &buf
->records_lost_full
);
1826 * Next subbuffer not being written to, and we
1827 * are either in overwrite mode or the buffer is
1828 * not full. It's safe to write in this new
1834 * Next subbuffer reserve offset does not match the
1835 * commit offset, and this did not involve update to the
1836 * reserve counter. Drop record in producer-consumer and
1837 * overwrite mode. Caused by either a writer OOPS or
1838 * too many nested writes over a reserve/commit pair.
1840 v_inc(config
, &buf
->records_lost_wrap
);
1844 config
->cb
.record_header_size(config
, chan
,
1846 &offsets
->pre_header_padding
,
1849 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1852 if (unlikely(subbuf_offset(offsets
->begin
, chan
)
1853 + offsets
->size
> chan
->backend
.subbuf_size
)) {
1855 * Record too big for subbuffers, report error, don't
1856 * complete the sub-buffer switch.
1858 v_inc(config
, &buf
->records_lost_big
);
1862 * We just made a successful buffer switch and the
1863 * record fits in the new subbuffer. Let's write.
1868 * Record fits in the current buffer and we are not on a switch
1869 * boundary. It's safe to write.
1872 offsets
->end
= offsets
->begin
+ offsets
->size
;
1874 if (unlikely(subbuf_offset(offsets
->end
, chan
) == 0)) {
1876 * The offset_end will fall at the very beginning of the next
1879 offsets
->switch_new_end
= 1; /* For offsets->begin */
1884 static struct lib_ring_buffer
*get_current_buf(struct channel
*chan
, int cpu
)
1886 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1888 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
1889 return per_cpu_ptr(chan
->backend
.buf
, cpu
);
1891 return chan
->backend
.buf
;
1894 void lib_ring_buffer_lost_event_too_big(struct channel
*chan
)
1896 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1897 struct lib_ring_buffer
*buf
= get_current_buf(chan
, smp_processor_id());
1899 v_inc(config
, &buf
->records_lost_big
);
1901 EXPORT_SYMBOL_GPL(lib_ring_buffer_lost_event_too_big
);
1904 * lib_ring_buffer_reserve_slow - Atomic slot reservation in a buffer.
1905 * @ctx: ring buffer context.
1907 * Return : -NOBUFS if not enough space, -ENOSPC if event size too large,
1908 * -EIO for other errors, else returns 0.
1909 * It will take care of sub-buffer switching.
1911 int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx
*ctx
)
1913 struct channel
*chan
= ctx
->chan
;
1914 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1915 struct lib_ring_buffer
*buf
;
1916 struct switch_offsets offsets
;
1919 ctx
->buf
= buf
= get_current_buf(chan
, ctx
->cpu
);
1923 ret
= lib_ring_buffer_try_reserve_slow(buf
, chan
, &offsets
,
1927 } while (unlikely(v_cmpxchg(config
, &buf
->offset
, offsets
.old
,
1932 * Atomically update last_tsc. This update races against concurrent
1933 * atomic updates, but the race will always cause supplementary full TSC
1934 * records, never the opposite (missing a full TSC record when it would
1937 save_last_tsc(config
, buf
, ctx
->tsc
);
1940 * Push the reader if necessary
1942 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.end
- 1);
1945 * Clear noref flag for this subbuffer.
1947 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
1948 subbuf_index(offsets
.end
- 1, chan
));
1951 * Switch old subbuffer if needed.
1953 if (unlikely(offsets
.switch_old_end
)) {
1954 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
1955 subbuf_index(offsets
.old
- 1, chan
));
1956 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, ctx
->tsc
);
1960 * Populate new subbuffer.
1962 if (unlikely(offsets
.switch_new_start
))
1963 lib_ring_buffer_switch_new_start(buf
, chan
, &offsets
, ctx
->tsc
);
1965 if (unlikely(offsets
.switch_new_end
))
1966 lib_ring_buffer_switch_new_end(buf
, chan
, &offsets
, ctx
->tsc
);
1968 ctx
->slot_size
= offsets
.size
;
1969 ctx
->pre_offset
= offsets
.begin
;
1970 ctx
->buf_offset
= offsets
.begin
+ offsets
.pre_header_padding
;
1973 EXPORT_SYMBOL_GPL(lib_ring_buffer_reserve_slow
);
1976 void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config
*config
,
1977 struct lib_ring_buffer
*buf
,
1978 unsigned long commit_count
,
1981 if (config
->oops
== RING_BUFFER_OOPS_CONSISTENCY
)
1982 v_set(config
, &buf
->commit_hot
[idx
].seq
, commit_count
);
1985 void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config
*config
,
1986 struct lib_ring_buffer
*buf
,
1987 struct channel
*chan
,
1988 unsigned long offset
,
1989 unsigned long commit_count
,
1993 unsigned long old_commit_count
= commit_count
1994 - chan
->backend
.subbuf_size
;
1997 * If we succeeded at updating cc_sb below, we are the subbuffer
1998 * writer delivering the subbuffer. Deals with concurrent
1999 * updates of the "cc" value without adding a add_return atomic
2000 * operation to the fast path.
2002 * We are doing the delivery in two steps:
2003 * - First, we cmpxchg() cc_sb to the new value
2004 * old_commit_count + 1. This ensures that we are the only
2005 * subbuffer user successfully filling the subbuffer, but we
2006 * do _not_ set the cc_sb value to "commit_count" yet.
2007 * Therefore, other writers that would wrap around the ring
2008 * buffer and try to start writing to our subbuffer would
2009 * have to drop records, because it would appear as
2011 * We therefore have exclusive access to the subbuffer control
2012 * structures. This mutual exclusion with other writers is
2013 * crucially important to perform record overruns count in
2014 * flight recorder mode locklessly.
2015 * - When we are ready to release the subbuffer (either for
2016 * reading or for overrun by other writers), we simply set the
2017 * cc_sb value to "commit_count" and perform delivery.
2019 * The subbuffer size is least 2 bytes (minimum size: 1 page).
2020 * This guarantees that old_commit_count + 1 != commit_count.
2024 * Order prior updates to reserve count prior to the
2025 * commit_cold cc_sb update.
2028 if (likely(v_cmpxchg(config
, &buf
->commit_cold
[idx
].cc_sb
,
2029 old_commit_count
, old_commit_count
+ 1)
2030 == old_commit_count
)) {
2032 * Start of exclusive subbuffer access. We are
2033 * guaranteed to be the last writer in this subbuffer
2034 * and any other writer trying to access this subbuffer
2035 * in this state is required to drop records.
2038 subbuffer_get_records_count(config
,
2039 &buf
->backend
, idx
),
2040 &buf
->records_count
);
2042 subbuffer_count_records_overrun(config
,
2045 &buf
->records_overrun
);
2046 config
->cb
.buffer_end(buf
, tsc
, idx
,
2047 lib_ring_buffer_get_data_size(config
,
2052 * Increment the packet counter while we have exclusive
2055 subbuffer_inc_packet_count(config
, &buf
->backend
, idx
);
2058 * Set noref flag and offset for this subbuffer id.
2059 * Contains a memory barrier that ensures counter stores
2060 * are ordered before set noref and offset.
2062 lib_ring_buffer_set_noref_offset(config
, &buf
->backend
, idx
,
2063 buf_trunc_val(offset
, chan
));
2066 * Order set_noref and record counter updates before the
2067 * end of subbuffer exclusive access. Orders with
2068 * respect to writers coming into the subbuffer after
2069 * wrap around, and also order wrt concurrent readers.
2072 /* End of exclusive subbuffer access */
2073 v_set(config
, &buf
->commit_cold
[idx
].cc_sb
,
2076 * Order later updates to reserve count after
2077 * the commit_cold cc_sb update.
2080 lib_ring_buffer_vmcore_check_deliver(config
, buf
,
2084 * RING_BUFFER_WAKEUP_BY_WRITER wakeup is not lock-free.
2086 if (config
->wakeup
== RING_BUFFER_WAKEUP_BY_WRITER
2087 && atomic_long_read(&buf
->active_readers
)
2088 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
2089 wake_up_interruptible(&buf
->read_wait
);
2090 wake_up_interruptible(&chan
->read_wait
);
2095 EXPORT_SYMBOL_GPL(lib_ring_buffer_check_deliver_slow
);
2097 int __init
init_lib_ring_buffer_frontend(void)
2101 for_each_possible_cpu(cpu
)
2102 spin_lock_init(&per_cpu(ring_buffer_nohz_lock
, cpu
));
2106 module_init(init_lib_ring_buffer_frontend
);
2108 void __exit
exit_lib_ring_buffer_frontend(void)
2112 module_exit(exit_lib_ring_buffer_frontend
);