1 #ifndef _LIB_RING_BUFFER_FRONTEND_INTERNAL_H
2 #define _LIB_RING_BUFFER_FRONTEND_INTERNAL_H
5 * linux/ringbuffer/frontend_internal.h
7 * Ring Buffer Library Synchronization Header (internal helpers).
9 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; only
14 * version 2.1 of the License.
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
26 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
28 * See ring_buffer_frontend.c for more information on wait-free algorithms.
31 #include "../../wrapper/ringbuffer/config.h"
32 #include "../../wrapper/ringbuffer/backend_types.h"
33 #include "../../wrapper/ringbuffer/frontend_types.h"
34 #include "../../lib/prio_heap/lttng_prio_heap.h" /* For per-CPU read-side iterator */
36 /* Buffer offset macros */
38 /* buf_trunc mask selects only the buffer number. */
40 unsigned long buf_trunc(unsigned long offset
, struct channel
*chan
)
42 return offset
& ~(chan
->backend
.buf_size
- 1);
46 /* Select the buffer number value (counter). */
48 unsigned long buf_trunc_val(unsigned long offset
, struct channel
*chan
)
50 return buf_trunc(offset
, chan
) >> chan
->backend
.buf_size_order
;
53 /* buf_offset mask selects only the offset within the current buffer. */
55 unsigned long buf_offset(unsigned long offset
, struct channel
*chan
)
57 return offset
& (chan
->backend
.buf_size
- 1);
60 /* subbuf_offset mask selects the offset within the current subbuffer. */
62 unsigned long subbuf_offset(unsigned long offset
, struct channel
*chan
)
64 return offset
& (chan
->backend
.subbuf_size
- 1);
67 /* subbuf_trunc mask selects the subbuffer number. */
69 unsigned long subbuf_trunc(unsigned long offset
, struct channel
*chan
)
71 return offset
& ~(chan
->backend
.subbuf_size
- 1);
74 /* subbuf_align aligns the offset to the next subbuffer. */
76 unsigned long subbuf_align(unsigned long offset
, struct channel
*chan
)
78 return (offset
+ chan
->backend
.subbuf_size
)
79 & ~(chan
->backend
.subbuf_size
- 1);
82 /* subbuf_index returns the index of the current subbuffer within the buffer. */
84 unsigned long subbuf_index(unsigned long offset
, struct channel
*chan
)
86 return buf_offset(offset
, chan
) >> chan
->backend
.subbuf_size_order
;
90 * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
91 * bits from the last TSC read. When overflows are detected, the full 64-bit
92 * timestamp counter should be written in the record header. Reads and writes
93 * last_tsc atomically.
96 #if (BITS_PER_LONG == 32)
98 void save_last_tsc(const struct lib_ring_buffer_config
*config
,
99 struct lib_ring_buffer
*buf
, u64 tsc
)
101 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
105 * Ensure the compiler performs this update in a single instruction.
107 v_set(config
, &buf
->last_tsc
, (unsigned long)(tsc
>> config
->tsc_bits
));
111 int last_tsc_overflow(const struct lib_ring_buffer_config
*config
,
112 struct lib_ring_buffer
*buf
, u64 tsc
)
114 unsigned long tsc_shifted
;
116 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
119 tsc_shifted
= (unsigned long)(tsc
>> config
->tsc_bits
);
120 if (unlikely(tsc_shifted
121 - (unsigned long)v_read(config
, &buf
->last_tsc
)))
128 void save_last_tsc(const struct lib_ring_buffer_config
*config
,
129 struct lib_ring_buffer
*buf
, u64 tsc
)
131 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
134 v_set(config
, &buf
->last_tsc
, (unsigned long)tsc
);
138 int last_tsc_overflow(const struct lib_ring_buffer_config
*config
,
139 struct lib_ring_buffer
*buf
, u64 tsc
)
141 if (config
->tsc_bits
== 0 || config
->tsc_bits
== 64)
144 if (unlikely((tsc
- v_read(config
, &buf
->last_tsc
))
145 >> config
->tsc_bits
))
153 int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx
*ctx
);
156 void lib_ring_buffer_switch_slow(struct lib_ring_buffer
*buf
,
157 enum switch_mode mode
);
159 /* Buffer write helpers */
162 void lib_ring_buffer_reserve_push_reader(struct lib_ring_buffer
*buf
,
163 struct channel
*chan
,
164 unsigned long offset
)
166 unsigned long consumed_old
, consumed_new
;
169 consumed_old
= atomic_long_read(&buf
->consumed
);
171 * If buffer is in overwrite mode, push the reader consumed
172 * count if the write position has reached it and we are not
173 * at the first iteration (don't push the reader farther than
174 * the writer). This operation can be done concurrently by many
175 * writers in the same buffer, the writer being at the farthest
176 * write position sub-buffer index in the buffer being the one
177 * which will win this loop.
179 if (unlikely(subbuf_trunc(offset
, chan
)
180 - subbuf_trunc(consumed_old
, chan
)
181 >= chan
->backend
.buf_size
))
182 consumed_new
= subbuf_align(consumed_old
, chan
);
185 } while (unlikely(atomic_long_cmpxchg(&buf
->consumed
, consumed_old
,
186 consumed_new
) != consumed_old
));
190 void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config
*config
,
191 struct lib_ring_buffer
*buf
,
192 unsigned long commit_count
,
195 if (config
->oops
== RING_BUFFER_OOPS_CONSISTENCY
)
196 v_set(config
, &buf
->commit_hot
[idx
].seq
, commit_count
);
200 int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config
*config
,
201 struct lib_ring_buffer
*buf
,
202 struct channel
*chan
)
204 unsigned long consumed_old
, consumed_idx
, commit_count
, write_offset
;
206 consumed_old
= atomic_long_read(&buf
->consumed
);
207 consumed_idx
= subbuf_index(consumed_old
, chan
);
208 commit_count
= v_read(config
, &buf
->commit_cold
[consumed_idx
].cc_sb
);
210 * No memory barrier here, since we are only interested
211 * in a statistically correct polling result. The next poll will
212 * get the data is we are racing. The mb() that ensures correct
213 * memory order is in get_subbuf.
215 write_offset
= v_read(config
, &buf
->offset
);
218 * Check that the subbuffer we are trying to consume has been
219 * already fully committed.
222 if (((commit_count
- chan
->backend
.subbuf_size
)
223 & chan
->commit_count_mask
)
224 - (buf_trunc(consumed_old
, chan
)
225 >> chan
->backend
.num_subbuf_order
)
230 * Check that we are not about to read the same subbuffer in
231 * which the writer head is.
233 if (subbuf_trunc(write_offset
, chan
) - subbuf_trunc(consumed_old
, chan
)
242 int lib_ring_buffer_pending_data(const struct lib_ring_buffer_config
*config
,
243 struct lib_ring_buffer
*buf
,
244 struct channel
*chan
)
246 return !!subbuf_offset(v_read(config
, &buf
->offset
), chan
);
250 unsigned long lib_ring_buffer_get_data_size(const struct lib_ring_buffer_config
*config
,
251 struct lib_ring_buffer
*buf
,
254 return subbuffer_get_data_size(config
, &buf
->backend
, idx
);
258 * Check if all space reservation in a buffer have been committed. This helps
259 * knowing if an execution context is nested (for per-cpu buffers only).
260 * This is a very specific ftrace use-case, so we keep this as "internal" API.
263 int lib_ring_buffer_reserve_committed(const struct lib_ring_buffer_config
*config
,
264 struct lib_ring_buffer
*buf
,
265 struct channel
*chan
)
267 unsigned long offset
, idx
, commit_count
;
269 CHAN_WARN_ON(chan
, config
->alloc
!= RING_BUFFER_ALLOC_PER_CPU
);
270 CHAN_WARN_ON(chan
, config
->sync
!= RING_BUFFER_SYNC_PER_CPU
);
273 * Read offset and commit count in a loop so they are both read
274 * atomically wrt interrupts. By deal with interrupt concurrency by
275 * restarting both reads if the offset has been pushed. Note that given
276 * we only have to deal with interrupt concurrency here, an interrupt
277 * modifying the commit count will also modify "offset", so it is safe
278 * to only check for offset modifications.
281 offset
= v_read(config
, &buf
->offset
);
282 idx
= subbuf_index(offset
, chan
);
283 commit_count
= v_read(config
, &buf
->commit_hot
[idx
].cc
);
284 } while (offset
!= v_read(config
, &buf
->offset
));
286 return ((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
287 - (commit_count
& chan
->commit_count_mask
) == 0);
291 void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config
*config
,
292 struct lib_ring_buffer
*buf
,
293 struct channel
*chan
,
294 unsigned long offset
,
295 unsigned long commit_count
,
298 unsigned long old_commit_count
= commit_count
299 - chan
->backend
.subbuf_size
;
302 /* Check if all commits have been done */
303 if (unlikely((buf_trunc(offset
, chan
) >> chan
->backend
.num_subbuf_order
)
304 - (old_commit_count
& chan
->commit_count_mask
) == 0)) {
306 * If we succeeded at updating cc_sb below, we are the subbuffer
307 * writer delivering the subbuffer. Deals with concurrent
308 * updates of the "cc" value without adding a add_return atomic
309 * operation to the fast path.
311 * We are doing the delivery in two steps:
312 * - First, we cmpxchg() cc_sb to the new value
313 * old_commit_count + 1. This ensures that we are the only
314 * subbuffer user successfully filling the subbuffer, but we
315 * do _not_ set the cc_sb value to "commit_count" yet.
316 * Therefore, other writers that would wrap around the ring
317 * buffer and try to start writing to our subbuffer would
318 * have to drop records, because it would appear as
320 * We therefore have exclusive access to the subbuffer control
321 * structures. This mutual exclusion with other writers is
322 * crucially important to perform record overruns count in
323 * flight recorder mode locklessly.
324 * - When we are ready to release the subbuffer (either for
325 * reading or for overrun by other writers), we simply set the
326 * cc_sb value to "commit_count" and perform delivery.
328 * The subbuffer size is least 2 bytes (minimum size: 1 page).
329 * This guarantees that old_commit_count + 1 != commit_count.
331 if (likely(v_cmpxchg(config
, &buf
->commit_cold
[idx
].cc_sb
,
332 old_commit_count
, old_commit_count
+ 1)
333 == old_commit_count
)) {
335 * Start of exclusive subbuffer access. We are
336 * guaranteed to be the last writer in this subbuffer
337 * and any other writer trying to access this subbuffer
338 * in this state is required to drop records.
340 tsc
= config
->cb
.ring_buffer_clock_read(chan
);
342 subbuffer_get_records_count(config
,
344 &buf
->records_count
);
346 subbuffer_count_records_overrun(config
,
349 &buf
->records_overrun
);
350 config
->cb
.buffer_end(buf
, tsc
, idx
,
351 lib_ring_buffer_get_data_size(config
,
356 * Set noref flag and offset for this subbuffer id.
357 * Contains a memory barrier that ensures counter stores
358 * are ordered before set noref and offset.
360 lib_ring_buffer_set_noref_offset(config
, &buf
->backend
, idx
,
361 buf_trunc_val(offset
, chan
));
364 * Order set_noref and record counter updates before the
365 * end of subbuffer exclusive access. Orders with
366 * respect to writers coming into the subbuffer after
367 * wrap around, and also order wrt concurrent readers.
370 /* End of exclusive subbuffer access */
371 v_set(config
, &buf
->commit_cold
[idx
].cc_sb
,
373 lib_ring_buffer_vmcore_check_deliver(config
, buf
,
377 * RING_BUFFER_WAKEUP_BY_WRITER wakeup is not lock-free.
379 if (config
->wakeup
== RING_BUFFER_WAKEUP_BY_WRITER
380 && atomic_long_read(&buf
->active_readers
)
381 && lib_ring_buffer_poll_deliver(config
, buf
, chan
)) {
382 wake_up_interruptible(&buf
->read_wait
);
383 wake_up_interruptible(&chan
->read_wait
);
391 * lib_ring_buffer_write_commit_counter
393 * For flight recording. must be called after commit.
394 * This function increments the subbuffer's commit_seq counter each time the
395 * commit count reaches back the reserve offset (modulo subbuffer size). It is
396 * useful for crash dump.
399 void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config
*config
,
400 struct lib_ring_buffer
*buf
,
401 struct channel
*chan
,
403 unsigned long buf_offset
,
404 unsigned long commit_count
,
407 unsigned long offset
, commit_seq_old
;
409 if (config
->oops
!= RING_BUFFER_OOPS_CONSISTENCY
)
412 offset
= buf_offset
+ slot_size
;
415 * subbuf_offset includes commit_count_mask. We can simply
416 * compare the offsets within the subbuffer without caring about
417 * buffer full/empty mismatch because offset is never zero here
418 * (subbuffer header and record headers have non-zero length).
420 if (unlikely(subbuf_offset(offset
- commit_count
, chan
)))
423 commit_seq_old
= v_read(config
, &buf
->commit_hot
[idx
].seq
);
424 while ((long) (commit_seq_old
- commit_count
) < 0)
425 commit_seq_old
= v_cmpxchg(config
, &buf
->commit_hot
[idx
].seq
,
426 commit_seq_old
, commit_count
);
429 extern int lib_ring_buffer_create(struct lib_ring_buffer
*buf
,
430 struct channel_backend
*chanb
, int cpu
);
431 extern void lib_ring_buffer_free(struct lib_ring_buffer
*buf
);
433 /* Keep track of trap nesting inside ring buffer code */
434 DECLARE_PER_CPU(unsigned int, lib_ring_buffer_nesting
);
436 #endif /* _LIB_RING_BUFFER_FRONTEND_INTERNAL_H */