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>
57 #include <asm/cacheflush.h>
59 #include <wrapper/ringbuffer/config.h>
60 #include <wrapper/ringbuffer/backend.h>
61 #include <wrapper/ringbuffer/frontend.h>
62 #include <wrapper/ringbuffer/iterator.h>
63 #include <wrapper/ringbuffer/nohz.h>
64 #include <wrapper/atomic.h>
65 #include <wrapper/kref.h>
66 #include <wrapper/percpu-defs.h>
67 #include <wrapper/timer.h>
68 #include <wrapper/vmalloc.h>
71 * Internal structure representing offsets to use at a sub-buffer switch.
73 struct switch_offsets
{
74 unsigned long begin
, end
, old
;
75 size_t pre_header_padding
, size
;
76 unsigned int switch_new_start
:1, switch_new_end
:1, switch_old_start
:1,
87 static ATOMIC_NOTIFIER_HEAD(tick_nohz_notifier
);
88 #endif /* CONFIG_NO_HZ */
90 static DEFINE_PER_CPU(spinlock_t
, ring_buffer_nohz_lock
);
92 DEFINE_PER_CPU(unsigned int, lib_ring_buffer_nesting
);
93 EXPORT_PER_CPU_SYMBOL(lib_ring_buffer_nesting
);
96 void lib_ring_buffer_print_errors(struct channel
*chan
,
97 struct lib_ring_buffer
*buf
, int cpu
);
99 void _lib_ring_buffer_switch_remote(struct lib_ring_buffer
*buf
,
100 enum switch_mode mode
);
103 int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config
*config
,
104 struct lib_ring_buffer
*buf
,
105 struct channel
*chan
)
107 unsigned long consumed_old
, consumed_idx
, commit_count
, write_offset
;
109 consumed_old
= atomic_long_read(&buf
->consumed
);
110 consumed_idx
= subbuf_index(consumed_old
, chan
);
111 commit_count
= v_read(config
, &buf
->commit_cold
[consumed_idx
].cc_sb
);
113 * No memory barrier here, since we are only interested
114 * in a statistically correct polling result. The next poll will
115 * get the data is we are racing. The mb() that ensures correct
116 * memory order is in get_subbuf.
118 write_offset
= v_read(config
, &buf
->offset
);
121 * Check that the subbuffer we are trying to consume has been
122 * already fully committed.
125 if (((commit_count
- chan
->backend
.subbuf_size
)
126 & chan
->commit_count_mask
)
127 - (buf_trunc(consumed_old
, chan
)
128 >> chan
->backend
.num_subbuf_order
)
133 * Check that we are not about to read the same subbuffer in
134 * which the writer head is.
136 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_old
, chan
)
144 * Must be called under cpu hotplug protection.
146 void lib_ring_buffer_free(struct lib_ring_buffer
*buf
)
148 struct channel
*chan
= buf
->backend
.chan
;
150 lib_ring_buffer_print_errors(chan
, buf
, buf
->backend
.cpu
);
151 lttng_kvfree(buf
->commit_hot
);
152 lttng_kvfree(buf
->commit_cold
);
154 lib_ring_buffer_backend_free(&buf
->backend
);
158 * lib_ring_buffer_reset - Reset ring buffer to initial values.
161 * Effectively empty the ring buffer. Should be called when the buffer is not
162 * used for writing. The ring buffer can be opened for reading, but the reader
163 * should not be using the iterator concurrently with reset. The previous
164 * current iterator record is reset.
166 void lib_ring_buffer_reset(struct lib_ring_buffer
*buf
)
168 struct channel
*chan
= buf
->backend
.chan
;
169 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
173 * Reset iterator first. It will put the subbuffer if it currently holds
176 lib_ring_buffer_iterator_reset(buf
);
177 v_set(config
, &buf
->offset
, 0);
178 for (i
= 0; i
< chan
->backend
.num_subbuf
; i
++) {
179 v_set(config
, &buf
->commit_hot
[i
].cc
, 0);
180 v_set(config
, &buf
->commit_hot
[i
].seq
, 0);
181 v_set(config
, &buf
->commit_cold
[i
].cc_sb
, 0);
183 atomic_long_set(&buf
->consumed
, 0);
184 atomic_set(&buf
->record_disabled
, 0);
185 v_set(config
, &buf
->last_tsc
, 0);
186 lib_ring_buffer_backend_reset(&buf
->backend
);
187 /* Don't reset number of active readers */
188 v_set(config
, &buf
->records_lost_full
, 0);
189 v_set(config
, &buf
->records_lost_wrap
, 0);
190 v_set(config
, &buf
->records_lost_big
, 0);
191 v_set(config
, &buf
->records_count
, 0);
192 v_set(config
, &buf
->records_overrun
, 0);
195 EXPORT_SYMBOL_GPL(lib_ring_buffer_reset
);
198 * channel_reset - Reset channel to initial values.
201 * Effectively empty the channel. Should be called when the channel is not used
202 * for writing. The channel can be opened for reading, but the reader should not
203 * be using the iterator concurrently with reset. The previous current iterator
206 void channel_reset(struct channel
*chan
)
209 * Reset iterators first. Will put the subbuffer if held for reading.
211 channel_iterator_reset(chan
);
212 atomic_set(&chan
->record_disabled
, 0);
213 /* Don't reset commit_count_mask, still valid */
214 channel_backend_reset(&chan
->backend
);
215 /* Don't reset switch/read timer interval */
216 /* Don't reset notifiers and notifier enable bits */
217 /* Don't reset reader reference count */
219 EXPORT_SYMBOL_GPL(channel_reset
);
222 * Must be called under cpu hotplug protection.
224 int lib_ring_buffer_create(struct lib_ring_buffer
*buf
,
225 struct channel_backend
*chanb
, int cpu
)
227 const struct lib_ring_buffer_config
*config
= &chanb
->config
;
228 struct channel
*chan
= container_of(chanb
, struct channel
, backend
);
229 void *priv
= chanb
->priv
;
230 size_t subbuf_header_size
;
234 /* Test for cpu hotplug */
235 if (buf
->backend
.allocated
)
239 * Paranoia: per cpu dynamic allocation is not officially documented as
240 * zeroing the memory, so let's do it here too, just in case.
242 memset(buf
, 0, sizeof(*buf
));
244 ret
= lib_ring_buffer_backend_create(&buf
->backend
, &chan
->backend
, cpu
);
249 lttng_kvzalloc_node(ALIGN(sizeof(*buf
->commit_hot
)
250 * chan
->backend
.num_subbuf
,
251 1 << INTERNODE_CACHE_SHIFT
),
252 GFP_KERNEL
| __GFP_NOWARN
,
253 cpu_to_node(max(cpu
, 0)));
254 if (!buf
->commit_hot
) {
260 lttng_kvzalloc_node(ALIGN(sizeof(*buf
->commit_cold
)
261 * chan
->backend
.num_subbuf
,
262 1 << INTERNODE_CACHE_SHIFT
),
263 GFP_KERNEL
| __GFP_NOWARN
,
264 cpu_to_node(max(cpu
, 0)));
265 if (!buf
->commit_cold
) {
270 init_waitqueue_head(&buf
->read_wait
);
271 init_waitqueue_head(&buf
->write_wait
);
272 raw_spin_lock_init(&buf
->raw_tick_nohz_spinlock
);
275 * Write the subbuffer header for first subbuffer so we know the total
276 * duration of data gathering.
278 subbuf_header_size
= config
->cb
.subbuffer_header_size();
279 v_set(config
, &buf
->offset
, subbuf_header_size
);
280 subbuffer_id_clear_noref(config
, &buf
->backend
.buf_wsb
[0].id
);
281 tsc
= config
->cb
.ring_buffer_clock_read(buf
->backend
.chan
);
282 config
->cb
.buffer_begin(buf
, tsc
, 0);
283 v_add(config
, subbuf_header_size
, &buf
->commit_hot
[0].cc
);
285 if (config
->cb
.buffer_create
) {
286 ret
= config
->cb
.buffer_create(buf
, priv
, cpu
, chanb
->name
);
292 * Ensure the buffer is ready before setting it to allocated and setting
294 * Used for cpu hotplug vs cpumask iteration.
297 buf
->backend
.allocated
= 1;
299 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
300 CHAN_WARN_ON(chan
, cpumask_test_cpu(cpu
,
301 chan
->backend
.cpumask
));
302 cpumask_set_cpu(cpu
, chan
->backend
.cpumask
);
309 lttng_kvfree(buf
->commit_cold
);
311 lttng_kvfree(buf
->commit_hot
);
313 lib_ring_buffer_backend_free(&buf
->backend
);
317 static void switch_buffer_timer(LTTNG_TIMER_FUNC_ARG_TYPE t
)
319 struct lib_ring_buffer
*buf
= lttng_from_timer(buf
, t
, switch_timer
);
320 struct channel
*chan
= buf
->backend
.chan
;
321 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
324 * Only flush buffers periodically if readers are active.
326 if (atomic_long_read(&buf
->active_readers
))
327 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
329 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
330 lttng_mod_timer_pinned(&buf
->switch_timer
,
331 jiffies
+ chan
->switch_timer_interval
);
333 mod_timer(&buf
->switch_timer
,
334 jiffies
+ chan
->switch_timer_interval
);
338 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
340 static void lib_ring_buffer_start_switch_timer(struct lib_ring_buffer
*buf
)
342 struct channel
*chan
= buf
->backend
.chan
;
343 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
344 unsigned int flags
= 0;
346 if (!chan
->switch_timer_interval
|| buf
->switch_timer_enabled
)
349 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
350 flags
= LTTNG_TIMER_PINNED
;
352 lttng_timer_setup(&buf
->switch_timer
, switch_buffer_timer
, flags
, buf
);
353 buf
->switch_timer
.expires
= jiffies
+ chan
->switch_timer_interval
;
355 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
356 add_timer_on(&buf
->switch_timer
, buf
->backend
.cpu
);
358 add_timer(&buf
->switch_timer
);
360 buf
->switch_timer_enabled
= 1;
364 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
366 static void lib_ring_buffer_stop_switch_timer(struct lib_ring_buffer
*buf
)
368 struct channel
*chan
= buf
->backend
.chan
;
370 if (!chan
->switch_timer_interval
|| !buf
->switch_timer_enabled
)
373 del_timer_sync(&buf
->switch_timer
);
374 buf
->switch_timer_enabled
= 0;
378 * Polling timer to check the channels for data.
380 static void read_buffer_timer(LTTNG_TIMER_FUNC_ARG_TYPE t
)
382 struct lib_ring_buffer
*buf
= lttng_from_timer(buf
, t
, read_timer
);
383 struct channel
*chan
= buf
->backend
.chan
;
384 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
386 CHAN_WARN_ON(chan
, !buf
->backend
.allocated
);
388 if (atomic_long_read(&buf
->active_readers
)
389 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
390 wake_up_interruptible(&buf
->read_wait
);
391 wake_up_interruptible(&chan
->read_wait
);
394 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
395 lttng_mod_timer_pinned(&buf
->read_timer
,
396 jiffies
+ chan
->read_timer_interval
);
398 mod_timer(&buf
->read_timer
,
399 jiffies
+ chan
->read_timer_interval
);
403 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
405 static void lib_ring_buffer_start_read_timer(struct lib_ring_buffer
*buf
)
407 struct channel
*chan
= buf
->backend
.chan
;
408 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
411 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
412 || !chan
->read_timer_interval
413 || buf
->read_timer_enabled
)
416 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
417 flags
= LTTNG_TIMER_PINNED
;
419 lttng_timer_setup(&buf
->read_timer
, read_buffer_timer
, flags
, buf
);
420 buf
->read_timer
.expires
= jiffies
+ chan
->read_timer_interval
;
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
);
427 buf
->read_timer_enabled
= 1;
431 * Called with ring_buffer_nohz_lock held for per-cpu buffers.
433 static void lib_ring_buffer_stop_read_timer(struct lib_ring_buffer
*buf
)
435 struct channel
*chan
= buf
->backend
.chan
;
436 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
438 if (config
->wakeup
!= RING_BUFFER_WAKEUP_BY_TIMER
439 || !chan
->read_timer_interval
440 || !buf
->read_timer_enabled
)
443 del_timer_sync(&buf
->read_timer
);
445 * do one more check to catch data that has been written in the last
448 if (lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
449 wake_up_interruptible(&buf
->read_wait
);
450 wake_up_interruptible(&chan
->read_wait
);
452 buf
->read_timer_enabled
= 0;
455 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0))
457 enum cpuhp_state lttng_rb_hp_prepare
;
458 enum cpuhp_state lttng_rb_hp_online
;
460 void lttng_rb_set_hp_prepare(enum cpuhp_state val
)
462 lttng_rb_hp_prepare
= val
;
464 EXPORT_SYMBOL_GPL(lttng_rb_set_hp_prepare
);
466 void lttng_rb_set_hp_online(enum cpuhp_state val
)
468 lttng_rb_hp_online
= val
;
470 EXPORT_SYMBOL_GPL(lttng_rb_set_hp_online
);
472 int lttng_cpuhp_rb_frontend_dead(unsigned int cpu
,
473 struct lttng_cpuhp_node
*node
)
475 struct channel
*chan
= container_of(node
, struct channel
,
477 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
, cpu
);
478 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
480 CHAN_WARN_ON(chan
, config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
);
483 * Performing a buffer switch on a remote CPU. Performed by
484 * the CPU responsible for doing the hotunplug after the target
485 * CPU stopped running completely. Ensures that all data
486 * from that remote CPU is flushed.
488 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
491 EXPORT_SYMBOL_GPL(lttng_cpuhp_rb_frontend_dead
);
493 int lttng_cpuhp_rb_frontend_online(unsigned int cpu
,
494 struct lttng_cpuhp_node
*node
)
496 struct channel
*chan
= container_of(node
, struct channel
,
498 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
, cpu
);
499 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
501 CHAN_WARN_ON(chan
, config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
);
503 wake_up_interruptible(&chan
->hp_wait
);
504 lib_ring_buffer_start_switch_timer(buf
);
505 lib_ring_buffer_start_read_timer(buf
);
508 EXPORT_SYMBOL_GPL(lttng_cpuhp_rb_frontend_online
);
510 int lttng_cpuhp_rb_frontend_offline(unsigned int cpu
,
511 struct lttng_cpuhp_node
*node
)
513 struct channel
*chan
= container_of(node
, struct channel
,
515 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
, cpu
);
516 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
518 CHAN_WARN_ON(chan
, config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
);
520 lib_ring_buffer_stop_switch_timer(buf
);
521 lib_ring_buffer_stop_read_timer(buf
);
524 EXPORT_SYMBOL_GPL(lttng_cpuhp_rb_frontend_offline
);
526 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
528 #ifdef CONFIG_HOTPLUG_CPU
531 * lib_ring_buffer_cpu_hp_callback - CPU hotplug callback
532 * @nb: notifier block
533 * @action: hotplug action to take
536 * Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
539 int lib_ring_buffer_cpu_hp_callback(struct notifier_block
*nb
,
540 unsigned long action
,
543 unsigned int cpu
= (unsigned long)hcpu
;
544 struct channel
*chan
= container_of(nb
, struct channel
,
546 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
, cpu
);
547 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
549 if (!chan
->cpu_hp_enable
)
552 CHAN_WARN_ON(chan
, config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
);
555 case CPU_DOWN_FAILED
:
556 case CPU_DOWN_FAILED_FROZEN
:
558 case CPU_ONLINE_FROZEN
:
559 wake_up_interruptible(&chan
->hp_wait
);
560 lib_ring_buffer_start_switch_timer(buf
);
561 lib_ring_buffer_start_read_timer(buf
);
564 case CPU_DOWN_PREPARE
:
565 case CPU_DOWN_PREPARE_FROZEN
:
566 lib_ring_buffer_stop_switch_timer(buf
);
567 lib_ring_buffer_stop_read_timer(buf
);
571 case CPU_DEAD_FROZEN
:
573 * Performing a buffer switch on a remote CPU. Performed by
574 * the CPU responsible for doing the hotunplug after the target
575 * CPU stopped running completely. Ensures that all data
576 * from that remote CPU is flushed.
578 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
588 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
590 #if defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER)
592 * For per-cpu buffers, call the reader wakeups before switching the buffer, so
593 * that wake-up-tracing generated events are flushed before going idle (in
594 * tick_nohz). We test if the spinlock is locked to deal with the race where
595 * readers try to sample the ring buffer before we perform the switch. We let
596 * the readers retry in that case. If there is data in the buffer, the wake up
597 * is going to forbid the CPU running the reader thread from going idle.
599 static int notrace
ring_buffer_tick_nohz_callback(struct notifier_block
*nb
,
603 struct channel
*chan
= container_of(nb
, struct channel
,
605 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
606 struct lib_ring_buffer
*buf
;
607 int cpu
= smp_processor_id();
609 if (config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
) {
611 * We don't support keeping the system idle with global buffers
612 * and streaming active. In order to do so, we would need to
613 * sample a non-nohz-cpumask racelessly with the nohz updates
614 * without adding synchronization overhead to nohz. Leave this
615 * use-case out for now.
620 buf
= channel_get_ring_buffer(config
, chan
, cpu
);
622 case TICK_NOHZ_FLUSH
:
623 raw_spin_lock(&buf
->raw_tick_nohz_spinlock
);
624 if (config
->wakeup
== RING_BUFFER_WAKEUP_BY_TIMER
625 && chan
->read_timer_interval
626 && atomic_long_read(&buf
->active_readers
)
627 && (lib_ring_buffer_poll_deliver(config
, buf
, chan
)
628 || lib_ring_buffer_pending_data(config
, buf
, chan
))) {
629 wake_up_interruptible(&buf
->read_wait
);
630 wake_up_interruptible(&chan
->read_wait
);
632 if (chan
->switch_timer_interval
)
633 lib_ring_buffer_switch_slow(buf
, SWITCH_ACTIVE
);
634 raw_spin_unlock(&buf
->raw_tick_nohz_spinlock
);
637 spin_lock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
638 lib_ring_buffer_stop_switch_timer(buf
);
639 lib_ring_buffer_stop_read_timer(buf
);
640 spin_unlock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
642 case TICK_NOHZ_RESTART
:
643 spin_lock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
644 lib_ring_buffer_start_read_timer(buf
);
645 lib_ring_buffer_start_switch_timer(buf
);
646 spin_unlock(lttng_this_cpu_ptr(&ring_buffer_nohz_lock
));
653 void notrace
lib_ring_buffer_tick_nohz_flush(void)
655 atomic_notifier_call_chain(&tick_nohz_notifier
, TICK_NOHZ_FLUSH
,
659 void notrace
lib_ring_buffer_tick_nohz_stop(void)
661 atomic_notifier_call_chain(&tick_nohz_notifier
, TICK_NOHZ_STOP
,
665 void notrace
lib_ring_buffer_tick_nohz_restart(void)
667 atomic_notifier_call_chain(&tick_nohz_notifier
, TICK_NOHZ_RESTART
,
670 #endif /* defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER) */
675 static void channel_unregister_notifiers(struct channel
*chan
)
677 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
679 channel_iterator_unregister_notifiers(chan
);
680 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
683 * Remove the nohz notifier first, so we are certain we stop
686 atomic_notifier_chain_unregister(&tick_nohz_notifier
,
687 &chan
->tick_nohz_notifier
);
689 * ring_buffer_nohz_lock will not be needed below, because
690 * we just removed the notifiers, which were the only source of
693 #endif /* CONFIG_NO_HZ */
694 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0))
698 ret
= cpuhp_state_remove_instance(lttng_rb_hp_online
,
699 &chan
->cpuhp_online
.node
);
701 ret
= cpuhp_state_remove_instance_nocalls(lttng_rb_hp_prepare
,
702 &chan
->cpuhp_prepare
.node
);
705 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
709 #ifdef CONFIG_HOTPLUG_CPU
711 chan
->cpu_hp_enable
= 0;
712 for_each_online_cpu(cpu
) {
713 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
715 lib_ring_buffer_stop_switch_timer(buf
);
716 lib_ring_buffer_stop_read_timer(buf
);
719 unregister_cpu_notifier(&chan
->cpu_hp_notifier
);
721 for_each_possible_cpu(cpu
) {
722 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
724 lib_ring_buffer_stop_switch_timer(buf
);
725 lib_ring_buffer_stop_read_timer(buf
);
729 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
731 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
733 lib_ring_buffer_stop_switch_timer(buf
);
734 lib_ring_buffer_stop_read_timer(buf
);
736 channel_backend_unregister_notifiers(&chan
->backend
);
739 static void lib_ring_buffer_set_quiescent(struct lib_ring_buffer
*buf
)
741 if (!buf
->quiescent
) {
742 buf
->quiescent
= true;
743 _lib_ring_buffer_switch_remote(buf
, SWITCH_FLUSH
);
747 static void lib_ring_buffer_clear_quiescent(struct lib_ring_buffer
*buf
)
749 buf
->quiescent
= false;
752 void lib_ring_buffer_set_quiescent_channel(struct channel
*chan
)
755 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
757 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
759 for_each_channel_cpu(cpu
, chan
) {
760 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
763 lib_ring_buffer_set_quiescent(buf
);
767 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
769 lib_ring_buffer_set_quiescent(buf
);
772 EXPORT_SYMBOL_GPL(lib_ring_buffer_set_quiescent_channel
);
774 void lib_ring_buffer_clear_quiescent_channel(struct channel
*chan
)
777 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
779 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
781 for_each_channel_cpu(cpu
, chan
) {
782 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
785 lib_ring_buffer_clear_quiescent(buf
);
789 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
791 lib_ring_buffer_clear_quiescent(buf
);
794 EXPORT_SYMBOL_GPL(lib_ring_buffer_clear_quiescent_channel
);
796 static void channel_free(struct channel
*chan
)
798 if (chan
->backend
.release_priv_ops
) {
799 chan
->backend
.release_priv_ops(chan
->backend
.priv_ops
);
801 channel_iterator_free(chan
);
802 channel_backend_free(&chan
->backend
);
807 * channel_create - Create channel.
808 * @config: ring buffer instance configuration
809 * @name: name of the channel
810 * @priv: ring buffer client private data
811 * @buf_addr: pointer the the beginning of the preallocated buffer contiguous
812 * address mapping. It is used only by RING_BUFFER_STATIC
813 * configuration. It can be set to NULL for other backends.
814 * @subbuf_size: subbuffer size
815 * @num_subbuf: number of subbuffers
816 * @switch_timer_interval: Time interval (in us) to fill sub-buffers with
817 * padding to let readers get those sub-buffers.
818 * Used for live streaming.
819 * @read_timer_interval: Time interval (in us) to wake up pending readers.
822 * Returns NULL on failure.
824 struct channel
*channel_create(const struct lib_ring_buffer_config
*config
,
825 const char *name
, void *priv
, void *buf_addr
,
827 size_t num_subbuf
, unsigned int switch_timer_interval
,
828 unsigned int read_timer_interval
)
831 struct channel
*chan
;
833 if (lib_ring_buffer_check_config(config
, switch_timer_interval
,
834 read_timer_interval
))
837 chan
= kzalloc(sizeof(struct channel
), GFP_KERNEL
);
841 ret
= channel_backend_init(&chan
->backend
, name
, config
, priv
,
842 subbuf_size
, num_subbuf
);
846 ret
= channel_iterator_init(chan
);
848 goto error_free_backend
;
850 chan
->commit_count_mask
= (~0UL >> chan
->backend
.num_subbuf_order
);
851 chan
->switch_timer_interval
= usecs_to_jiffies(switch_timer_interval
);
852 chan
->read_timer_interval
= usecs_to_jiffies(read_timer_interval
);
853 kref_init(&chan
->ref
);
854 init_waitqueue_head(&chan
->read_wait
);
855 init_waitqueue_head(&chan
->hp_wait
);
857 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
858 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0))
859 chan
->cpuhp_prepare
.component
= LTTNG_RING_BUFFER_FRONTEND
;
860 ret
= cpuhp_state_add_instance_nocalls(lttng_rb_hp_prepare
,
861 &chan
->cpuhp_prepare
.node
);
863 goto cpuhp_prepare_error
;
865 chan
->cpuhp_online
.component
= LTTNG_RING_BUFFER_FRONTEND
;
866 ret
= cpuhp_state_add_instance(lttng_rb_hp_online
,
867 &chan
->cpuhp_online
.node
);
869 goto cpuhp_online_error
;
870 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
874 * In case of non-hotplug cpu, if the ring-buffer is allocated
875 * in early initcall, it will not be notified of secondary cpus.
876 * In that off case, we need to allocate for all possible cpus.
878 #ifdef CONFIG_HOTPLUG_CPU
879 chan
->cpu_hp_notifier
.notifier_call
=
880 lib_ring_buffer_cpu_hp_callback
;
881 chan
->cpu_hp_notifier
.priority
= 6;
882 register_cpu_notifier(&chan
->cpu_hp_notifier
);
885 for_each_online_cpu(cpu
) {
886 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
888 spin_lock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
889 lib_ring_buffer_start_switch_timer(buf
);
890 lib_ring_buffer_start_read_timer(buf
);
891 spin_unlock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
893 chan
->cpu_hp_enable
= 1;
896 for_each_possible_cpu(cpu
) {
897 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
899 spin_lock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
900 lib_ring_buffer_start_switch_timer(buf
);
901 lib_ring_buffer_start_read_timer(buf
);
902 spin_unlock(&per_cpu(ring_buffer_nohz_lock
, cpu
));
906 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
908 #if defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER)
909 /* Only benefit from NO_HZ idle with per-cpu buffers for now. */
910 chan
->tick_nohz_notifier
.notifier_call
=
911 ring_buffer_tick_nohz_callback
;
912 chan
->tick_nohz_notifier
.priority
= ~0U;
913 atomic_notifier_chain_register(&tick_nohz_notifier
,
914 &chan
->tick_nohz_notifier
);
915 #endif /* defined(CONFIG_NO_HZ) && defined(CONFIG_LIB_RING_BUFFER) */
918 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
920 lib_ring_buffer_start_switch_timer(buf
);
921 lib_ring_buffer_start_read_timer(buf
);
926 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0))
928 ret
= cpuhp_state_remove_instance_nocalls(lttng_rb_hp_prepare
,
929 &chan
->cpuhp_prepare
.node
);
932 #endif /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,10,0)) */
934 channel_backend_free(&chan
->backend
);
939 EXPORT_SYMBOL_GPL(channel_create
);
942 void channel_release(struct kref
*kref
)
944 struct channel
*chan
= container_of(kref
, struct channel
, ref
);
949 * channel_destroy - Finalize, wait for q.s. and destroy channel.
950 * @chan: channel to destroy
953 * Call "destroy" callback, finalize channels, and then decrement the
954 * channel reference count. Note that when readers have completed data
955 * consumption of finalized channels, get_subbuf() will return -ENODATA.
956 * They should release their handle at that point. Returns the private
959 void *channel_destroy(struct channel
*chan
)
962 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
965 channel_unregister_notifiers(chan
);
967 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
969 * No need to hold cpu hotplug, because all notifiers have been
972 for_each_channel_cpu(cpu
, chan
) {
973 struct lib_ring_buffer
*buf
= per_cpu_ptr(chan
->backend
.buf
,
976 if (config
->cb
.buffer_finalize
)
977 config
->cb
.buffer_finalize(buf
,
980 if (buf
->backend
.allocated
)
981 lib_ring_buffer_set_quiescent(buf
);
983 * Perform flush before writing to finalized.
986 ACCESS_ONCE(buf
->finalized
) = 1;
987 wake_up_interruptible(&buf
->read_wait
);
990 struct lib_ring_buffer
*buf
= chan
->backend
.buf
;
992 if (config
->cb
.buffer_finalize
)
993 config
->cb
.buffer_finalize(buf
, chan
->backend
.priv
, -1);
994 if (buf
->backend
.allocated
)
995 lib_ring_buffer_set_quiescent(buf
);
997 * Perform flush before writing to finalized.
1000 ACCESS_ONCE(buf
->finalized
) = 1;
1001 wake_up_interruptible(&buf
->read_wait
);
1003 ACCESS_ONCE(chan
->finalized
) = 1;
1004 wake_up_interruptible(&chan
->hp_wait
);
1005 wake_up_interruptible(&chan
->read_wait
);
1006 priv
= chan
->backend
.priv
;
1007 kref_put(&chan
->ref
, channel_release
);
1010 EXPORT_SYMBOL_GPL(channel_destroy
);
1012 struct lib_ring_buffer
*channel_get_ring_buffer(
1013 const struct lib_ring_buffer_config
*config
,
1014 struct channel
*chan
, int cpu
)
1016 if (config
->alloc
== RING_BUFFER_ALLOC_GLOBAL
)
1017 return chan
->backend
.buf
;
1019 return per_cpu_ptr(chan
->backend
.buf
, cpu
);
1021 EXPORT_SYMBOL_GPL(channel_get_ring_buffer
);
1023 int lib_ring_buffer_open_read(struct lib_ring_buffer
*buf
)
1025 struct channel
*chan
= buf
->backend
.chan
;
1027 if (!atomic_long_add_unless(&buf
->active_readers
, 1, 1))
1029 if (!lttng_kref_get(&chan
->ref
)) {
1030 atomic_long_dec(&buf
->active_readers
);
1033 lttng_smp_mb__after_atomic();
1036 EXPORT_SYMBOL_GPL(lib_ring_buffer_open_read
);
1038 void lib_ring_buffer_release_read(struct lib_ring_buffer
*buf
)
1040 struct channel
*chan
= buf
->backend
.chan
;
1042 CHAN_WARN_ON(chan
, atomic_long_read(&buf
->active_readers
) != 1);
1043 lttng_smp_mb__before_atomic();
1044 atomic_long_dec(&buf
->active_readers
);
1045 kref_put(&chan
->ref
, channel_release
);
1047 EXPORT_SYMBOL_GPL(lib_ring_buffer_release_read
);
1050 * Promote compiler barrier to a smp_mb().
1051 * For the specific ring buffer case, this IPI call should be removed if the
1052 * architecture does not reorder writes. This should eventually be provided by
1053 * a separate architecture-specific infrastructure.
1055 static void remote_mb(void *info
)
1061 * lib_ring_buffer_snapshot - save subbuffer position snapshot (for read)
1063 * @consumed: consumed count indicating the position where to read
1064 * @produced: produced count, indicates position when to stop reading
1066 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
1067 * data to read at consumed position, or 0 if the get operation succeeds.
1068 * Busy-loop trying to get data if the tick_nohz sequence lock is held.
1071 int lib_ring_buffer_snapshot(struct lib_ring_buffer
*buf
,
1072 unsigned long *consumed
, unsigned long *produced
)
1074 struct channel
*chan
= buf
->backend
.chan
;
1075 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1076 unsigned long consumed_cur
, write_offset
;
1080 finalized
= ACCESS_ONCE(buf
->finalized
);
1082 * Read finalized before counters.
1085 consumed_cur
= atomic_long_read(&buf
->consumed
);
1087 * No need to issue a memory barrier between consumed count read and
1088 * write offset read, because consumed count can only change
1089 * concurrently in overwrite mode, and we keep a sequence counter
1090 * identifier derived from the write offset to check we are getting
1091 * the same sub-buffer we are expecting (the sub-buffers are atomically
1092 * "tagged" upon writes, tags are checked upon read).
1094 write_offset
= v_read(config
, &buf
->offset
);
1097 * Check that we are not about to read the same subbuffer in
1098 * which the writer head is.
1100 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_cur
, chan
)
1104 *consumed
= consumed_cur
;
1105 *produced
= subbuf_trunc(write_offset
, chan
);
1111 * The memory barriers __wait_event()/wake_up_interruptible() take care
1112 * of "raw_spin_is_locked" memory ordering.
1116 else if (raw_spin_is_locked(&buf
->raw_tick_nohz_spinlock
))
1121 EXPORT_SYMBOL_GPL(lib_ring_buffer_snapshot
);
1124 * Performs the same function as lib_ring_buffer_snapshot(), but the positions
1125 * are saved regardless of whether the consumed and produced positions are
1126 * in the same subbuffer.
1128 * @consumed: consumed byte count indicating the last position read
1129 * @produced: produced byte count indicating the last position written
1131 * This function is meant to provide information on the exact producer and
1132 * consumer positions without regard for the "snapshot" feature.
1134 int lib_ring_buffer_snapshot_sample_positions(struct lib_ring_buffer
*buf
,
1135 unsigned long *consumed
, unsigned long *produced
)
1137 struct channel
*chan
= buf
->backend
.chan
;
1138 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1141 *consumed
= atomic_long_read(&buf
->consumed
);
1143 * No need to issue a memory barrier between consumed count read and
1144 * write offset read, because consumed count can only change
1145 * concurrently in overwrite mode, and we keep a sequence counter
1146 * identifier derived from the write offset to check we are getting
1147 * the same sub-buffer we are expecting (the sub-buffers are atomically
1148 * "tagged" upon writes, tags are checked upon read).
1150 *produced
= v_read(config
, &buf
->offset
);
1155 * lib_ring_buffer_put_snapshot - move consumed counter forward
1157 * Should only be called from consumer context.
1159 * @consumed_new: new consumed count value
1161 void lib_ring_buffer_move_consumer(struct lib_ring_buffer
*buf
,
1162 unsigned long consumed_new
)
1164 struct lib_ring_buffer_backend
*bufb
= &buf
->backend
;
1165 struct channel
*chan
= bufb
->chan
;
1166 unsigned long consumed
;
1168 CHAN_WARN_ON(chan
, atomic_long_read(&buf
->active_readers
) != 1);
1171 * Only push the consumed value forward.
1172 * If the consumed cmpxchg fails, this is because we have been pushed by
1173 * the writer in flight recorder mode.
1175 consumed
= atomic_long_read(&buf
->consumed
);
1176 while ((long) consumed
- (long) consumed_new
< 0)
1177 consumed
= atomic_long_cmpxchg(&buf
->consumed
, consumed
,
1179 /* Wake-up the metadata producer */
1180 wake_up_interruptible(&buf
->write_wait
);
1182 EXPORT_SYMBOL_GPL(lib_ring_buffer_move_consumer
);
1184 #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
1185 static void lib_ring_buffer_flush_read_subbuf_dcache(
1186 const struct lib_ring_buffer_config
*config
,
1187 struct channel
*chan
,
1188 struct lib_ring_buffer
*buf
)
1190 struct lib_ring_buffer_backend_pages
*pages
;
1191 unsigned long sb_bindex
, id
, i
, nr_pages
;
1193 if (config
->output
!= RING_BUFFER_MMAP
)
1197 * Architectures with caches aliased on virtual addresses may
1198 * use different cache lines for the linear mapping vs
1199 * user-space memory mapping. Given that the ring buffer is
1200 * based on the kernel linear mapping, aligning it with the
1201 * user-space mapping is not straightforward, and would require
1202 * extra TLB entries. Therefore, simply flush the dcache for the
1203 * entire sub-buffer before reading it.
1205 id
= buf
->backend
.buf_rsb
.id
;
1206 sb_bindex
= subbuffer_id_get_index(config
, id
);
1207 pages
= buf
->backend
.array
[sb_bindex
];
1208 nr_pages
= buf
->backend
.num_pages_per_subbuf
;
1209 for (i
= 0; i
< nr_pages
; i
++) {
1210 struct lib_ring_buffer_backend_page
*backend_page
;
1212 backend_page
= &pages
->p
[i
];
1213 flush_dcache_page(pfn_to_page(backend_page
->pfn
));
1217 static void lib_ring_buffer_flush_read_subbuf_dcache(
1218 const struct lib_ring_buffer_config
*config
,
1219 struct channel
*chan
,
1220 struct lib_ring_buffer
*buf
)
1226 * lib_ring_buffer_get_subbuf - get exclusive access to subbuffer for reading
1228 * @consumed: consumed count indicating the position where to read
1230 * Returns -ENODATA if buffer is finalized, -EAGAIN if there is currently no
1231 * data to read at consumed position, or 0 if the get operation succeeds.
1232 * Busy-loop trying to get data if the tick_nohz sequence lock is held.
1234 int lib_ring_buffer_get_subbuf(struct lib_ring_buffer
*buf
,
1235 unsigned long consumed
)
1237 struct channel
*chan
= buf
->backend
.chan
;
1238 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1239 unsigned long consumed_cur
, consumed_idx
, commit_count
, write_offset
;
1243 if (buf
->get_subbuf
) {
1245 * Reader is trying to get a subbuffer twice.
1247 CHAN_WARN_ON(chan
, 1);
1251 finalized
= ACCESS_ONCE(buf
->finalized
);
1253 * Read finalized before counters.
1256 consumed_cur
= atomic_long_read(&buf
->consumed
);
1257 consumed_idx
= subbuf_index(consumed
, chan
);
1258 commit_count
= v_read(config
, &buf
->commit_cold
[consumed_idx
].cc_sb
);
1260 * Make sure we read the commit count before reading the buffer
1261 * data and the write offset. Correct consumed offset ordering
1262 * wrt commit count is insured by the use of cmpxchg to update
1263 * the consumed offset.
1264 * smp_call_function_single can fail if the remote CPU is offline,
1265 * this is OK because then there is no wmb to execute there.
1266 * If our thread is executing on the same CPU as the on the buffers
1267 * belongs to, we don't have to synchronize it at all. If we are
1268 * migrated, the scheduler will take care of the memory barriers.
1269 * Normally, smp_call_function_single() should ensure program order when
1270 * executing the remote function, which implies that it surrounds the
1271 * function execution with :
1282 * However, smp_call_function_single() does not seem to clearly execute
1283 * such barriers. It depends on spinlock semantic to provide the barrier
1284 * before executing the IPI and, when busy-looping, csd_lock_wait only
1285 * executes smp_mb() when it has to wait for the other CPU.
1287 * I don't trust this code. Therefore, let's add the smp_mb() sequence
1288 * required ourself, even if duplicated. It has no performance impact
1291 * smp_mb() is needed because smp_rmb() and smp_wmb() only order read vs
1292 * read and write vs write. They do not ensure core synchronization. We
1293 * really have to ensure total order between the 3 barriers running on
1296 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1297 if (config
->sync
== RING_BUFFER_SYNC_PER_CPU
1298 && config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
) {
1299 if (raw_smp_processor_id() != buf
->backend
.cpu
) {
1300 /* Total order with IPI handler smp_mb() */
1302 smp_call_function_single(buf
->backend
.cpu
,
1303 remote_mb
, NULL
, 1);
1304 /* Total order with IPI handler smp_mb() */
1308 /* Total order with IPI handler smp_mb() */
1310 smp_call_function(remote_mb
, NULL
, 1);
1311 /* Total order with IPI handler smp_mb() */
1316 * Local rmb to match the remote wmb to read the commit count
1317 * before the buffer data and the write offset.
1322 write_offset
= v_read(config
, &buf
->offset
);
1325 * Check that the buffer we are getting is after or at consumed_cur
1328 if ((long) subbuf_trunc(consumed
, chan
)
1329 - (long) subbuf_trunc(consumed_cur
, chan
) < 0)
1333 * Check that the subbuffer we are trying to consume has been
1334 * already fully committed.
1336 if (((commit_count
- chan
->backend
.subbuf_size
)
1337 & chan
->commit_count_mask
)
1338 - (buf_trunc(consumed
, chan
)
1339 >> chan
->backend
.num_subbuf_order
)
1344 * Check that we are not about to read the same subbuffer in
1345 * which the writer head is.
1347 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed
, chan
)
1352 * Failure to get the subbuffer causes a busy-loop retry without going
1353 * to a wait queue. These are caused by short-lived race windows where
1354 * the writer is getting access to a subbuffer we were trying to get
1355 * access to. Also checks that the "consumed" buffer count we are
1356 * looking for matches the one contained in the subbuffer id.
1358 ret
= update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
1359 consumed_idx
, buf_trunc_val(consumed
, chan
));
1362 subbuffer_id_clear_noref(config
, &buf
->backend
.buf_rsb
.id
);
1364 buf
->get_subbuf_consumed
= consumed
;
1365 buf
->get_subbuf
= 1;
1367 lib_ring_buffer_flush_read_subbuf_dcache(config
, chan
, buf
);
1373 * The memory barriers __wait_event()/wake_up_interruptible() take care
1374 * of "raw_spin_is_locked" memory ordering.
1378 else if (raw_spin_is_locked(&buf
->raw_tick_nohz_spinlock
))
1383 EXPORT_SYMBOL_GPL(lib_ring_buffer_get_subbuf
);
1386 * lib_ring_buffer_put_subbuf - release exclusive subbuffer access
1389 void lib_ring_buffer_put_subbuf(struct lib_ring_buffer
*buf
)
1391 struct lib_ring_buffer_backend
*bufb
= &buf
->backend
;
1392 struct channel
*chan
= bufb
->chan
;
1393 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1394 unsigned long read_sb_bindex
, consumed_idx
, consumed
;
1396 CHAN_WARN_ON(chan
, atomic_long_read(&buf
->active_readers
) != 1);
1398 if (!buf
->get_subbuf
) {
1400 * Reader puts a subbuffer it did not get.
1402 CHAN_WARN_ON(chan
, 1);
1405 consumed
= buf
->get_subbuf_consumed
;
1406 buf
->get_subbuf
= 0;
1409 * Clear the records_unread counter. (overruns counter)
1410 * Can still be non-zero if a file reader simply grabbed the data
1411 * without using iterators.
1412 * Can be below zero if an iterator is used on a snapshot more than
1415 read_sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
1416 v_add(config
, v_read(config
,
1417 &bufb
->array
[read_sb_bindex
]->records_unread
),
1418 &bufb
->records_read
);
1419 v_set(config
, &bufb
->array
[read_sb_bindex
]->records_unread
, 0);
1420 CHAN_WARN_ON(chan
, config
->mode
== RING_BUFFER_OVERWRITE
1421 && subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
1422 subbuffer_id_set_noref(config
, &bufb
->buf_rsb
.id
);
1425 * Exchange the reader subbuffer with the one we put in its place in the
1426 * writer subbuffer table. Expect the original consumed count. If
1427 * update_read_sb_index fails, this is because the writer updated the
1428 * subbuffer concurrently. We should therefore keep the subbuffer we
1429 * currently have: it has become invalid to try reading this sub-buffer
1430 * consumed count value anyway.
1432 consumed_idx
= subbuf_index(consumed
, chan
);
1433 update_read_sb_index(config
, &buf
->backend
, &chan
->backend
,
1434 consumed_idx
, buf_trunc_val(consumed
, chan
));
1436 * update_read_sb_index return value ignored. Don't exchange sub-buffer
1437 * if the writer concurrently updated it.
1440 EXPORT_SYMBOL_GPL(lib_ring_buffer_put_subbuf
);
1443 * cons_offset is an iterator on all subbuffer offsets between the reader
1444 * position and the writer position. (inclusive)
1447 void lib_ring_buffer_print_subbuffer_errors(struct lib_ring_buffer
*buf
,
1448 struct channel
*chan
,
1449 unsigned long cons_offset
,
1452 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1453 unsigned long cons_idx
, commit_count
, commit_count_sb
;
1455 cons_idx
= subbuf_index(cons_offset
, chan
);
1456 commit_count
= v_read(config
, &buf
->commit_hot
[cons_idx
].cc
);
1457 commit_count_sb
= v_read(config
, &buf
->commit_cold
[cons_idx
].cc_sb
);
1459 if (subbuf_offset(commit_count
, chan
) != 0)
1461 "ring buffer %s, cpu %d: "
1462 "commit count in subbuffer %lu,\n"
1463 "expecting multiples of %lu bytes\n"
1464 " [ %lu bytes committed, %lu bytes reader-visible ]\n",
1465 chan
->backend
.name
, cpu
, cons_idx
,
1466 chan
->backend
.subbuf_size
,
1467 commit_count
, commit_count_sb
);
1469 printk(KERN_DEBUG
"ring buffer: %s, cpu %d: %lu bytes committed\n",
1470 chan
->backend
.name
, cpu
, commit_count
);
1474 void lib_ring_buffer_print_buffer_errors(struct lib_ring_buffer
*buf
,
1475 struct channel
*chan
,
1476 void *priv
, int cpu
)
1478 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1479 unsigned long write_offset
, cons_offset
;
1482 * No need to order commit_count, write_offset and cons_offset reads
1483 * because we execute at teardown when no more writer nor reader
1484 * references are left.
1486 write_offset
= v_read(config
, &buf
->offset
);
1487 cons_offset
= atomic_long_read(&buf
->consumed
);
1488 if (write_offset
!= cons_offset
)
1490 "ring buffer %s, cpu %d: "
1491 "non-consumed data\n"
1492 " [ %lu bytes written, %lu bytes read ]\n",
1493 chan
->backend
.name
, cpu
, write_offset
, cons_offset
);
1495 for (cons_offset
= atomic_long_read(&buf
->consumed
);
1496 (long) (subbuf_trunc((unsigned long) v_read(config
, &buf
->offset
),
1499 cons_offset
= subbuf_align(cons_offset
, chan
))
1500 lib_ring_buffer_print_subbuffer_errors(buf
, chan
, cons_offset
,
1505 void lib_ring_buffer_print_errors(struct channel
*chan
,
1506 struct lib_ring_buffer
*buf
, int cpu
)
1508 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1509 void *priv
= chan
->backend
.priv
;
1511 if (!strcmp(chan
->backend
.name
, "relay-metadata")) {
1512 printk(KERN_DEBUG
"ring buffer %s: %lu records written, "
1513 "%lu records overrun\n",
1515 v_read(config
, &buf
->records_count
),
1516 v_read(config
, &buf
->records_overrun
));
1518 printk(KERN_DEBUG
"ring buffer %s, cpu %d: %lu records written, "
1519 "%lu records overrun\n",
1520 chan
->backend
.name
, cpu
,
1521 v_read(config
, &buf
->records_count
),
1522 v_read(config
, &buf
->records_overrun
));
1524 if (v_read(config
, &buf
->records_lost_full
)
1525 || v_read(config
, &buf
->records_lost_wrap
)
1526 || v_read(config
, &buf
->records_lost_big
))
1528 "ring buffer %s, cpu %d: records were lost. Caused by:\n"
1529 " [ %lu buffer full, %lu nest buffer wrap-around, "
1530 "%lu event too big ]\n",
1531 chan
->backend
.name
, cpu
,
1532 v_read(config
, &buf
->records_lost_full
),
1533 v_read(config
, &buf
->records_lost_wrap
),
1534 v_read(config
, &buf
->records_lost_big
));
1536 lib_ring_buffer_print_buffer_errors(buf
, chan
, priv
, cpu
);
1540 * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
1542 * Only executed when the buffer is finalized, in SWITCH_FLUSH.
1545 void lib_ring_buffer_switch_old_start(struct lib_ring_buffer
*buf
,
1546 struct channel
*chan
,
1547 struct switch_offsets
*offsets
,
1550 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1551 unsigned long oldidx
= subbuf_index(offsets
->old
, chan
);
1552 unsigned long commit_count
;
1553 struct commit_counters_hot
*cc_hot
;
1555 config
->cb
.buffer_begin(buf
, tsc
, oldidx
);
1558 * Order all writes to buffer before the commit count update that will
1559 * determine that the subbuffer is full.
1561 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1563 * Must write slot data before incrementing commit count. This
1564 * compiler barrier is upgraded into a smp_mb() by the IPI sent
1570 cc_hot
= &buf
->commit_hot
[oldidx
];
1571 v_add(config
, config
->cb
.subbuffer_header_size(), &cc_hot
->cc
);
1572 commit_count
= v_read(config
, &cc_hot
->cc
);
1573 /* Check if the written buffer has to be delivered */
1574 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
,
1575 commit_count
, oldidx
, tsc
);
1576 lib_ring_buffer_write_commit_counter(config
, buf
, chan
,
1577 offsets
->old
+ config
->cb
.subbuffer_header_size(),
1578 commit_count
, cc_hot
);
1582 * lib_ring_buffer_switch_old_end: switch old subbuffer
1584 * Note : offset_old should never be 0 here. It is ok, because we never perform
1585 * buffer switch on an empty subbuffer in SWITCH_ACTIVE mode. The caller
1586 * increments the offset_old value when doing a SWITCH_FLUSH on an empty
1590 void lib_ring_buffer_switch_old_end(struct lib_ring_buffer
*buf
,
1591 struct channel
*chan
,
1592 struct switch_offsets
*offsets
,
1595 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1596 unsigned long oldidx
= subbuf_index(offsets
->old
- 1, chan
);
1597 unsigned long commit_count
, padding_size
, data_size
;
1598 struct commit_counters_hot
*cc_hot
;
1600 data_size
= subbuf_offset(offsets
->old
- 1, chan
) + 1;
1601 padding_size
= chan
->backend
.subbuf_size
- data_size
;
1602 subbuffer_set_data_size(config
, &buf
->backend
, oldidx
, data_size
);
1605 * Order all writes to buffer before the commit count update that will
1606 * determine that the subbuffer is full.
1608 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1610 * Must write slot data before incrementing commit count. This
1611 * compiler barrier is upgraded into a smp_mb() by the IPI sent
1617 cc_hot
= &buf
->commit_hot
[oldidx
];
1618 v_add(config
, padding_size
, &cc_hot
->cc
);
1619 commit_count
= v_read(config
, &cc_hot
->cc
);
1620 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->old
- 1,
1621 commit_count
, oldidx
, tsc
);
1622 lib_ring_buffer_write_commit_counter(config
, buf
, chan
,
1623 offsets
->old
+ padding_size
, commit_count
,
1628 * lib_ring_buffer_switch_new_start: Populate new subbuffer.
1630 * This code can be executed unordered : writers may already have written to the
1631 * sub-buffer before this code gets executed, caution. The commit makes sure
1632 * that this code is executed before the deliver of this sub-buffer.
1635 void lib_ring_buffer_switch_new_start(struct lib_ring_buffer
*buf
,
1636 struct channel
*chan
,
1637 struct switch_offsets
*offsets
,
1640 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1641 unsigned long beginidx
= subbuf_index(offsets
->begin
, chan
);
1642 unsigned long commit_count
;
1643 struct commit_counters_hot
*cc_hot
;
1645 config
->cb
.buffer_begin(buf
, tsc
, beginidx
);
1648 * Order all writes to buffer before the commit count update that will
1649 * determine that the subbuffer is full.
1651 if (config
->ipi
== RING_BUFFER_IPI_BARRIER
) {
1653 * Must write slot data before incrementing commit count. This
1654 * compiler barrier is upgraded into a smp_mb() by the IPI sent
1660 cc_hot
= &buf
->commit_hot
[beginidx
];
1661 v_add(config
, config
->cb
.subbuffer_header_size(), &cc_hot
->cc
);
1662 commit_count
= v_read(config
, &cc_hot
->cc
);
1663 /* Check if the written buffer has to be delivered */
1664 lib_ring_buffer_check_deliver(config
, buf
, chan
, offsets
->begin
,
1665 commit_count
, beginidx
, tsc
);
1666 lib_ring_buffer_write_commit_counter(config
, buf
, chan
,
1667 offsets
->begin
+ config
->cb
.subbuffer_header_size(),
1668 commit_count
, cc_hot
);
1672 * lib_ring_buffer_switch_new_end: finish switching current subbuffer
1674 * Calls subbuffer_set_data_size() to set the data size of the current
1675 * sub-buffer. We do not need to perform check_deliver nor commit here,
1676 * since this task will be done by the "commit" of the event for which
1677 * we are currently doing the space reservation.
1680 void lib_ring_buffer_switch_new_end(struct lib_ring_buffer
*buf
,
1681 struct channel
*chan
,
1682 struct switch_offsets
*offsets
,
1685 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1686 unsigned long endidx
, data_size
;
1688 endidx
= subbuf_index(offsets
->end
- 1, chan
);
1689 data_size
= subbuf_offset(offsets
->end
- 1, chan
) + 1;
1690 subbuffer_set_data_size(config
, &buf
->backend
, endidx
, data_size
);
1696 * !0 if execution must be aborted.
1699 int lib_ring_buffer_try_switch_slow(enum switch_mode mode
,
1700 struct lib_ring_buffer
*buf
,
1701 struct channel
*chan
,
1702 struct switch_offsets
*offsets
,
1705 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1706 unsigned long off
, reserve_commit_diff
;
1708 offsets
->begin
= v_read(config
, &buf
->offset
);
1709 offsets
->old
= offsets
->begin
;
1710 offsets
->switch_old_start
= 0;
1711 off
= subbuf_offset(offsets
->begin
, chan
);
1713 *tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1716 * Ensure we flush the header of an empty subbuffer when doing the
1717 * finalize (SWITCH_FLUSH). This ensures that we end up knowing the
1718 * total data gathering duration even if there were no records saved
1719 * after the last buffer switch.
1720 * In SWITCH_ACTIVE mode, switch the buffer when it contains events.
1721 * SWITCH_ACTIVE only flushes the current subbuffer, dealing with end of
1722 * subbuffer header as appropriate.
1723 * The next record that reserves space will be responsible for
1724 * populating the following subbuffer header. We choose not to populate
1725 * the next subbuffer header here because we want to be able to use
1726 * SWITCH_ACTIVE for periodical buffer flush and CPU tick_nohz stop
1727 * buffer flush, which must guarantee that all the buffer content
1728 * (records and header timestamps) are visible to the reader. This is
1729 * required for quiescence guarantees for the fusion merge.
1731 if (mode
!= SWITCH_FLUSH
&& !off
)
1732 return -1; /* we do not have to switch : buffer is empty */
1734 if (unlikely(off
== 0)) {
1735 unsigned long sb_index
, commit_count
;
1738 * We are performing a SWITCH_FLUSH. At this stage, there are no
1739 * concurrent writes into the buffer.
1741 * The client does not save any header information. Don't
1742 * switch empty subbuffer on finalize, because it is invalid to
1743 * deliver a completely empty subbuffer.
1745 if (!config
->cb
.subbuffer_header_size())
1748 /* Test new buffer integrity */
1749 sb_index
= subbuf_index(offsets
->begin
, chan
);
1750 commit_count
= v_read(config
,
1751 &buf
->commit_cold
[sb_index
].cc_sb
);
1752 reserve_commit_diff
=
1753 (buf_trunc(offsets
->begin
, chan
)
1754 >> chan
->backend
.num_subbuf_order
)
1755 - (commit_count
& chan
->commit_count_mask
);
1756 if (likely(reserve_commit_diff
== 0)) {
1757 /* Next subbuffer not being written to. */
1758 if (unlikely(config
->mode
!= RING_BUFFER_OVERWRITE
&&
1759 subbuf_trunc(offsets
->begin
, chan
)
1760 - subbuf_trunc((unsigned long)
1761 atomic_long_read(&buf
->consumed
), chan
)
1762 >= chan
->backend
.buf_size
)) {
1764 * We do not overwrite non consumed buffers
1765 * and we are full : don't switch.
1770 * Next subbuffer not being written to, and we
1771 * are either in overwrite mode or the buffer is
1772 * not full. It's safe to write in this new
1778 * Next subbuffer reserve offset does not match the
1779 * commit offset. Don't perform switch in
1780 * producer-consumer and overwrite mode. Caused by
1781 * either a writer OOPS or too many nested writes over a
1782 * reserve/commit pair.
1788 * Need to write the subbuffer start header on finalize.
1790 offsets
->switch_old_start
= 1;
1792 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1793 /* Note: old points to the next subbuf at offset 0 */
1794 offsets
->end
= offsets
->begin
;
1799 * Force a sub-buffer switch. This operation is completely reentrant : can be
1800 * called while tracing is active with absolutely no lock held.
1802 * Note, however, that as a v_cmpxchg is used for some atomic
1803 * operations, this function must be called from the CPU which owns the buffer
1804 * for a ACTIVE flush.
1806 void lib_ring_buffer_switch_slow(struct lib_ring_buffer
*buf
, enum switch_mode mode
)
1808 struct channel
*chan
= buf
->backend
.chan
;
1809 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1810 struct switch_offsets offsets
;
1811 unsigned long oldidx
;
1817 * Perform retryable operations.
1820 if (lib_ring_buffer_try_switch_slow(mode
, buf
, chan
, &offsets
,
1822 return; /* Switch not needed */
1823 } while (v_cmpxchg(config
, &buf
->offset
, offsets
.old
, offsets
.end
)
1827 * Atomically update last_tsc. This update races against concurrent
1828 * atomic updates, but the race will always cause supplementary full TSC
1829 * records, never the opposite (missing a full TSC record when it would
1832 save_last_tsc(config
, buf
, tsc
);
1835 * Push the reader if necessary
1837 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.old
);
1839 oldidx
= subbuf_index(offsets
.old
, chan
);
1840 lib_ring_buffer_clear_noref(config
, &buf
->backend
, oldidx
);
1843 * May need to populate header start on SWITCH_FLUSH.
1845 if (offsets
.switch_old_start
) {
1846 lib_ring_buffer_switch_old_start(buf
, chan
, &offsets
, tsc
);
1847 offsets
.old
+= config
->cb
.subbuffer_header_size();
1851 * Switch old subbuffer.
1853 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, tsc
);
1855 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow
);
1857 struct switch_param
{
1858 struct lib_ring_buffer
*buf
;
1859 enum switch_mode mode
;
1862 static void remote_switch(void *info
)
1864 struct switch_param
*param
= info
;
1865 struct lib_ring_buffer
*buf
= param
->buf
;
1867 lib_ring_buffer_switch_slow(buf
, param
->mode
);
1870 static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer
*buf
,
1871 enum switch_mode mode
)
1873 struct channel
*chan
= buf
->backend
.chan
;
1874 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1876 struct switch_param param
;
1879 * With global synchronization we don't need to use the IPI scheme.
1881 if (config
->sync
== RING_BUFFER_SYNC_GLOBAL
) {
1882 lib_ring_buffer_switch_slow(buf
, mode
);
1887 * Disabling preemption ensures two things: first, that the
1888 * target cpu is not taken concurrently offline while we are within
1889 * smp_call_function_single(). Secondly, if it happens that the
1890 * CPU is not online, our own call to lib_ring_buffer_switch_slow()
1891 * needs to be protected from CPU hotplug handlers, which can
1892 * also perform a remote subbuffer switch.
1897 ret
= smp_call_function_single(buf
->backend
.cpu
,
1898 remote_switch
, ¶m
, 1);
1900 /* Remote CPU is offline, do it ourself. */
1901 lib_ring_buffer_switch_slow(buf
, mode
);
1906 /* Switch sub-buffer if current sub-buffer is non-empty. */
1907 void lib_ring_buffer_switch_remote(struct lib_ring_buffer
*buf
)
1909 _lib_ring_buffer_switch_remote(buf
, SWITCH_ACTIVE
);
1911 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote
);
1913 /* Switch sub-buffer even if current sub-buffer is empty. */
1914 void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer
*buf
)
1916 _lib_ring_buffer_switch_remote(buf
, SWITCH_FLUSH
);
1918 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote_empty
);
1923 * -ENOSPC if event size is too large for packet.
1924 * -ENOBUFS if there is currently not enough space in buffer for the event.
1925 * -EIO if data cannot be written into the buffer for any other reason.
1928 int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer
*buf
,
1929 struct channel
*chan
,
1930 struct switch_offsets
*offsets
,
1931 struct lib_ring_buffer_ctx
*ctx
,
1934 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
1935 unsigned long reserve_commit_diff
, offset_cmp
;
1938 offsets
->begin
= offset_cmp
= v_read(config
, &buf
->offset
);
1939 offsets
->old
= offsets
->begin
;
1940 offsets
->switch_new_start
= 0;
1941 offsets
->switch_new_end
= 0;
1942 offsets
->switch_old_end
= 0;
1943 offsets
->pre_header_padding
= 0;
1945 ctx
->tsc
= config
->cb
.ring_buffer_clock_read(chan
);
1946 if ((int64_t) ctx
->tsc
== -EIO
)
1949 if (last_tsc_overflow(config
, buf
, ctx
->tsc
))
1950 ctx
->rflags
|= RING_BUFFER_RFLAG_FULL_TSC
;
1952 if (unlikely(subbuf_offset(offsets
->begin
, ctx
->chan
) == 0)) {
1953 offsets
->switch_new_start
= 1; /* For offsets->begin */
1955 offsets
->size
= config
->cb
.record_header_size(config
, chan
,
1957 &offsets
->pre_header_padding
,
1960 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
1963 if (unlikely(subbuf_offset(offsets
->begin
, chan
) +
1964 offsets
->size
> chan
->backend
.subbuf_size
)) {
1965 offsets
->switch_old_end
= 1; /* For offsets->old */
1966 offsets
->switch_new_start
= 1; /* For offsets->begin */
1969 if (unlikely(offsets
->switch_new_start
)) {
1970 unsigned long sb_index
, commit_count
;
1973 * We are typically not filling the previous buffer completely.
1975 if (likely(offsets
->switch_old_end
))
1976 offsets
->begin
= subbuf_align(offsets
->begin
, chan
);
1977 offsets
->begin
= offsets
->begin
1978 + config
->cb
.subbuffer_header_size();
1979 /* Test new buffer integrity */
1980 sb_index
= subbuf_index(offsets
->begin
, chan
);
1982 * Read buf->offset before buf->commit_cold[sb_index].cc_sb.
1983 * lib_ring_buffer_check_deliver() has the matching
1984 * memory barriers required around commit_cold cc_sb
1985 * updates to ensure reserve and commit counter updates
1986 * are not seen reordered when updated by another CPU.
1989 commit_count
= v_read(config
,
1990 &buf
->commit_cold
[sb_index
].cc_sb
);
1991 /* Read buf->commit_cold[sb_index].cc_sb before buf->offset. */
1993 if (unlikely(offset_cmp
!= v_read(config
, &buf
->offset
))) {
1995 * The reserve counter have been concurrently updated
1996 * while we read the commit counter. This means the
1997 * commit counter we read might not match buf->offset
1998 * due to concurrent update. We therefore need to retry.
2002 reserve_commit_diff
=
2003 (buf_trunc(offsets
->begin
, chan
)
2004 >> chan
->backend
.num_subbuf_order
)
2005 - (commit_count
& chan
->commit_count_mask
);
2006 if (likely(reserve_commit_diff
== 0)) {
2007 /* Next subbuffer not being written to. */
2008 if (unlikely(config
->mode
!= RING_BUFFER_OVERWRITE
&&
2009 subbuf_trunc(offsets
->begin
, chan
)
2010 - subbuf_trunc((unsigned long)
2011 atomic_long_read(&buf
->consumed
), chan
)
2012 >= chan
->backend
.buf_size
)) {
2014 * We do not overwrite non consumed buffers
2015 * and we are full : record is lost.
2017 v_inc(config
, &buf
->records_lost_full
);
2021 * Next subbuffer not being written to, and we
2022 * are either in overwrite mode or the buffer is
2023 * not full. It's safe to write in this new
2029 * Next subbuffer reserve offset does not match the
2030 * commit offset, and this did not involve update to the
2031 * reserve counter. Drop record in producer-consumer and
2032 * overwrite mode. Caused by either a writer OOPS or
2033 * too many nested writes over a reserve/commit pair.
2035 v_inc(config
, &buf
->records_lost_wrap
);
2039 config
->cb
.record_header_size(config
, chan
,
2041 &offsets
->pre_header_padding
,
2044 lib_ring_buffer_align(offsets
->begin
+ offsets
->size
,
2047 if (unlikely(subbuf_offset(offsets
->begin
, chan
)
2048 + offsets
->size
> chan
->backend
.subbuf_size
)) {
2050 * Record too big for subbuffers, report error, don't
2051 * complete the sub-buffer switch.
2053 v_inc(config
, &buf
->records_lost_big
);
2057 * We just made a successful buffer switch and the
2058 * record fits in the new subbuffer. Let's write.
2063 * Record fits in the current buffer and we are not on a switch
2064 * boundary. It's safe to write.
2067 offsets
->end
= offsets
->begin
+ offsets
->size
;
2069 if (unlikely(subbuf_offset(offsets
->end
, chan
) == 0)) {
2071 * The offset_end will fall at the very beginning of the next
2074 offsets
->switch_new_end
= 1; /* For offsets->begin */
2079 static struct lib_ring_buffer
*get_current_buf(struct channel
*chan
, int cpu
)
2081 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
2083 if (config
->alloc
== RING_BUFFER_ALLOC_PER_CPU
)
2084 return per_cpu_ptr(chan
->backend
.buf
, cpu
);
2086 return chan
->backend
.buf
;
2089 void lib_ring_buffer_lost_event_too_big(struct channel
*chan
)
2091 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
2092 struct lib_ring_buffer
*buf
= get_current_buf(chan
, smp_processor_id());
2094 v_inc(config
, &buf
->records_lost_big
);
2096 EXPORT_SYMBOL_GPL(lib_ring_buffer_lost_event_too_big
);
2099 * lib_ring_buffer_reserve_slow - Atomic slot reservation in a buffer.
2100 * @ctx: ring buffer context.
2102 * Return : -NOBUFS if not enough space, -ENOSPC if event size too large,
2103 * -EIO for other errors, else returns 0.
2104 * It will take care of sub-buffer switching.
2106 int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx
*ctx
,
2109 struct channel
*chan
= ctx
->chan
;
2110 const struct lib_ring_buffer_config
*config
= &chan
->backend
.config
;
2111 struct lib_ring_buffer
*buf
;
2112 struct switch_offsets offsets
;
2115 ctx
->buf
= buf
= get_current_buf(chan
, ctx
->cpu
);
2119 ret
= lib_ring_buffer_try_reserve_slow(buf
, chan
, &offsets
,
2123 } while (unlikely(v_cmpxchg(config
, &buf
->offset
, offsets
.old
,
2128 * Atomically update last_tsc. This update races against concurrent
2129 * atomic updates, but the race will always cause supplementary full TSC
2130 * records, never the opposite (missing a full TSC record when it would
2133 save_last_tsc(config
, buf
, ctx
->tsc
);
2136 * Push the reader if necessary
2138 lib_ring_buffer_reserve_push_reader(buf
, chan
, offsets
.end
- 1);
2141 * Clear noref flag for this subbuffer.
2143 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
2144 subbuf_index(offsets
.end
- 1, chan
));
2147 * Switch old subbuffer if needed.
2149 if (unlikely(offsets
.switch_old_end
)) {
2150 lib_ring_buffer_clear_noref(config
, &buf
->backend
,
2151 subbuf_index(offsets
.old
- 1, chan
));
2152 lib_ring_buffer_switch_old_end(buf
, chan
, &offsets
, ctx
->tsc
);
2156 * Populate new subbuffer.
2158 if (unlikely(offsets
.switch_new_start
))
2159 lib_ring_buffer_switch_new_start(buf
, chan
, &offsets
, ctx
->tsc
);
2161 if (unlikely(offsets
.switch_new_end
))
2162 lib_ring_buffer_switch_new_end(buf
, chan
, &offsets
, ctx
->tsc
);
2164 ctx
->slot_size
= offsets
.size
;
2165 ctx
->pre_offset
= offsets
.begin
;
2166 ctx
->buf_offset
= offsets
.begin
+ offsets
.pre_header_padding
;
2169 EXPORT_SYMBOL_GPL(lib_ring_buffer_reserve_slow
);
2172 void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config
*config
,
2173 struct lib_ring_buffer
*buf
,
2174 unsigned long commit_count
,
2177 if (config
->oops
== RING_BUFFER_OOPS_CONSISTENCY
)
2178 v_set(config
, &buf
->commit_hot
[idx
].seq
, commit_count
);
2182 * The ring buffer can count events recorded and overwritten per buffer,
2183 * but it is disabled by default due to its performance overhead.
2185 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
2187 void deliver_count_events(const struct lib_ring_buffer_config
*config
,
2188 struct lib_ring_buffer
*buf
,
2191 v_add(config
, subbuffer_get_records_count(config
,
2192 &buf
->backend
, idx
),
2193 &buf
->records_count
);
2194 v_add(config
, subbuffer_count_records_overrun(config
,
2195 &buf
->backend
, idx
),
2196 &buf
->records_overrun
);
2198 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
2200 void deliver_count_events(const struct lib_ring_buffer_config
*config
,
2201 struct lib_ring_buffer
*buf
,
2205 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
2208 void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config
*config
,
2209 struct lib_ring_buffer
*buf
,
2210 struct channel
*chan
,
2211 unsigned long offset
,
2212 unsigned long commit_count
,
2216 unsigned long old_commit_count
= commit_count
2217 - chan
->backend
.subbuf_size
;
2220 * If we succeeded at updating cc_sb below, we are the subbuffer
2221 * writer delivering the subbuffer. Deals with concurrent
2222 * updates of the "cc" value without adding a add_return atomic
2223 * operation to the fast path.
2225 * We are doing the delivery in two steps:
2226 * - First, we cmpxchg() cc_sb to the new value
2227 * old_commit_count + 1. This ensures that we are the only
2228 * subbuffer user successfully filling the subbuffer, but we
2229 * do _not_ set the cc_sb value to "commit_count" yet.
2230 * Therefore, other writers that would wrap around the ring
2231 * buffer and try to start writing to our subbuffer would
2232 * have to drop records, because it would appear as
2234 * We therefore have exclusive access to the subbuffer control
2235 * structures. This mutual exclusion with other writers is
2236 * crucially important to perform record overruns count in
2237 * flight recorder mode locklessly.
2238 * - When we are ready to release the subbuffer (either for
2239 * reading or for overrun by other writers), we simply set the
2240 * cc_sb value to "commit_count" and perform delivery.
2242 * The subbuffer size is least 2 bytes (minimum size: 1 page).
2243 * This guarantees that old_commit_count + 1 != commit_count.
2247 * Order prior updates to reserve count prior to the
2248 * commit_cold cc_sb update.
2251 if (likely(v_cmpxchg(config
, &buf
->commit_cold
[idx
].cc_sb
,
2252 old_commit_count
, old_commit_count
+ 1)
2253 == old_commit_count
)) {
2255 * Start of exclusive subbuffer access. We are
2256 * guaranteed to be the last writer in this subbuffer
2257 * and any other writer trying to access this subbuffer
2258 * in this state is required to drop records.
2260 deliver_count_events(config
, buf
, idx
);
2261 config
->cb
.buffer_end(buf
, tsc
, idx
,
2262 lib_ring_buffer_get_data_size(config
,
2267 * Increment the packet counter while we have exclusive
2270 subbuffer_inc_packet_count(config
, &buf
->backend
, idx
);
2273 * Set noref flag and offset for this subbuffer id.
2274 * Contains a memory barrier that ensures counter stores
2275 * are ordered before set noref and offset.
2277 lib_ring_buffer_set_noref_offset(config
, &buf
->backend
, idx
,
2278 buf_trunc_val(offset
, chan
));
2281 * Order set_noref and record counter updates before the
2282 * end of subbuffer exclusive access. Orders with
2283 * respect to writers coming into the subbuffer after
2284 * wrap around, and also order wrt concurrent readers.
2287 /* End of exclusive subbuffer access */
2288 v_set(config
, &buf
->commit_cold
[idx
].cc_sb
,
2291 * Order later updates to reserve count after
2292 * the commit_cold cc_sb update.
2295 lib_ring_buffer_vmcore_check_deliver(config
, buf
,
2299 * RING_BUFFER_WAKEUP_BY_WRITER wakeup is not lock-free.
2301 if (config
->wakeup
== RING_BUFFER_WAKEUP_BY_WRITER
2302 && atomic_long_read(&buf
->active_readers
)
2303 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
2304 wake_up_interruptible(&buf
->read_wait
);
2305 wake_up_interruptible(&chan
->read_wait
);
2310 EXPORT_SYMBOL_GPL(lib_ring_buffer_check_deliver_slow
);
2312 int __init
init_lib_ring_buffer_frontend(void)
2316 for_each_possible_cpu(cpu
)
2317 spin_lock_init(&per_cpu(ring_buffer_nohz_lock
, cpu
));
2321 module_init(init_lib_ring_buffer_frontend
);
2323 void __exit
exit_lib_ring_buffer_frontend(void)
2327 module_exit(exit_lib_ring_buffer_frontend
);