1 #ifndef _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
2 #define _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
5 * linux/ringbuffer/backend_internal.h
7 * Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
9 * Ring buffer backend (internal helpers).
11 * Dual LGPL v2.1/GPL v2 license.
15 #include "backend_types.h"
16 #include "frontend_types.h"
18 /* Ring buffer backend API presented to the frontend */
20 /* Ring buffer and channel backend create/free */
22 int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend
*bufb
,
23 struct channel_backend
*chan
, int cpu
);
24 void channel_backend_unregister_notifiers(struct channel_backend
*chanb
);
25 void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend
*bufb
);
26 int channel_backend_init(struct channel_backend
*chanb
,
28 const struct lib_ring_buffer_config
*config
,
29 void *priv
, size_t subbuf_size
,
31 void channel_backend_free(struct channel_backend
*chanb
);
33 void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend
*bufb
);
34 void channel_backend_reset(struct channel_backend
*chanb
);
36 int lib_ring_buffer_backend_init(void);
37 void lib_ring_buffer_backend_exit(void);
39 extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend
*bufb
,
40 size_t offset
, const void *src
, size_t len
,
44 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
45 * exchanged atomically.
47 * Top half word, except lowest bit, belongs to "offset", which is used to keep
48 * to count the produced buffers. For overwrite mode, this provides the
49 * consumer with the capacity to read subbuffers in order, handling the
50 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
51 * systems) concurrently with a single execution of get_subbuf (between offset
52 * sampling and subbuffer ID exchange).
55 #define HALF_ULONG_BITS (BITS_PER_LONG >> 1)
57 #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
58 #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
59 #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
61 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
63 #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
64 #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
65 #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
67 * In overwrite mode: lowest half of word is used for index.
68 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
69 * In producer-consumer mode: whole word used for index.
71 #define SB_ID_INDEX_SHIFT 0
72 #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
73 #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
76 * Construct the subbuffer id from offset, index and noref. Use only the index
77 * for producer-consumer mode (offset and noref are only used in overwrite
81 unsigned long subbuffer_id(const struct lib_ring_buffer_config
*config
,
82 unsigned long offset
, unsigned long noref
,
85 if (config
->mode
== RING_BUFFER_OVERWRITE
)
86 return (offset
<< SB_ID_OFFSET_SHIFT
)
87 | (noref
<< SB_ID_NOREF_SHIFT
)
94 * Compare offset with the offset contained within id. Return 1 if the offset
95 * bits are identical, else 0.
98 int subbuffer_id_compare_offset(const struct lib_ring_buffer_config
*config
,
99 unsigned long id
, unsigned long offset
)
101 return (id
& SB_ID_OFFSET_MASK
) == (offset
<< SB_ID_OFFSET_SHIFT
);
105 unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config
*config
,
108 if (config
->mode
== RING_BUFFER_OVERWRITE
)
109 return id
& SB_ID_INDEX_MASK
;
115 unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config
*config
,
118 if (config
->mode
== RING_BUFFER_OVERWRITE
)
119 return !!(id
& SB_ID_NOREF_MASK
);
125 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
129 void subbuffer_id_set_noref(const struct lib_ring_buffer_config
*config
,
132 if (config
->mode
== RING_BUFFER_OVERWRITE
)
133 *id
|= SB_ID_NOREF_MASK
;
137 void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config
*config
,
138 unsigned long *id
, unsigned long offset
)
142 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
144 tmp
&= ~SB_ID_OFFSET_MASK
;
145 tmp
|= offset
<< SB_ID_OFFSET_SHIFT
;
146 tmp
|= SB_ID_NOREF_MASK
;
147 /* Volatile store, read concurrently by readers. */
148 ACCESS_ONCE(*id
) = tmp
;
152 /* No volatile access, since already used locally */
154 void subbuffer_id_clear_noref(const struct lib_ring_buffer_config
*config
,
157 if (config
->mode
== RING_BUFFER_OVERWRITE
)
158 *id
&= ~SB_ID_NOREF_MASK
;
162 * For overwrite mode, cap the number of subbuffers per buffer to:
163 * 2^16 on 32-bit architectures
164 * 2^32 on 64-bit architectures
165 * This is required to fit in the index part of the ID. Return 0 on success,
169 int subbuffer_id_check_index(const struct lib_ring_buffer_config
*config
,
170 unsigned long num_subbuf
)
172 if (config
->mode
== RING_BUFFER_OVERWRITE
)
173 return (num_subbuf
> (1UL << HALF_ULONG_BITS
)) ? -EPERM
: 0;
179 void subbuffer_count_record(const struct lib_ring_buffer_config
*config
,
180 struct lib_ring_buffer_backend
*bufb
,
183 unsigned long sb_bindex
;
185 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
186 v_inc(config
, &bufb
->array
[sb_bindex
]->records_commit
);
190 * Reader has exclusive subbuffer access for record consumption. No need to
191 * perform the decrement atomically.
194 void subbuffer_consume_record(const struct lib_ring_buffer_config
*config
,
195 struct lib_ring_buffer_backend
*bufb
)
197 unsigned long sb_bindex
;
199 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
200 CHAN_WARN_ON(bufb
->chan
,
201 !v_read(config
, &bufb
->array
[sb_bindex
]->records_unread
));
202 /* Non-atomic decrement protected by exclusive subbuffer access */
203 _v_dec(config
, &bufb
->array
[sb_bindex
]->records_unread
);
204 v_inc(config
, &bufb
->records_read
);
208 unsigned long subbuffer_get_records_count(
209 const struct lib_ring_buffer_config
*config
,
210 struct lib_ring_buffer_backend
*bufb
,
213 unsigned long sb_bindex
;
215 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
216 return v_read(config
, &bufb
->array
[sb_bindex
]->records_commit
);
220 * Must be executed at subbuffer delivery when the writer has _exclusive_
221 * subbuffer access. See ring_buffer_check_deliver() for details.
222 * ring_buffer_get_records_count() must be called to get the records count
223 * before this function, because it resets the records_commit count.
226 unsigned long subbuffer_count_records_overrun(
227 const struct lib_ring_buffer_config
*config
,
228 struct lib_ring_buffer_backend
*bufb
,
231 struct lib_ring_buffer_backend_pages
*pages
;
232 unsigned long overruns
, sb_bindex
;
234 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
235 pages
= bufb
->array
[sb_bindex
];
236 overruns
= v_read(config
, &pages
->records_unread
);
237 v_set(config
, &pages
->records_unread
,
238 v_read(config
, &pages
->records_commit
));
239 v_set(config
, &pages
->records_commit
, 0);
245 void subbuffer_set_data_size(const struct lib_ring_buffer_config
*config
,
246 struct lib_ring_buffer_backend
*bufb
,
248 unsigned long data_size
)
250 struct lib_ring_buffer_backend_pages
*pages
;
251 unsigned long sb_bindex
;
253 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
254 pages
= bufb
->array
[sb_bindex
];
255 pages
->data_size
= data_size
;
259 unsigned long subbuffer_get_read_data_size(
260 const struct lib_ring_buffer_config
*config
,
261 struct lib_ring_buffer_backend
*bufb
)
263 struct lib_ring_buffer_backend_pages
*pages
;
264 unsigned long sb_bindex
;
266 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
267 pages
= bufb
->array
[sb_bindex
];
268 return pages
->data_size
;
272 unsigned long subbuffer_get_data_size(
273 const struct lib_ring_buffer_config
*config
,
274 struct lib_ring_buffer_backend
*bufb
,
277 struct lib_ring_buffer_backend_pages
*pages
;
278 unsigned long sb_bindex
;
280 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
281 pages
= bufb
->array
[sb_bindex
];
282 return pages
->data_size
;
286 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
290 void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config
*config
,
291 struct lib_ring_buffer_backend
*bufb
,
294 unsigned long id
, new_id
;
296 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
300 * Performing a volatile access to read the sb_pages, because we want to
301 * read a coherent version of the pointer and the associated noref flag.
303 id
= ACCESS_ONCE(bufb
->buf_wsb
[idx
].id
);
305 /* This check is called on the fast path for each record. */
306 if (likely(!subbuffer_id_is_noref(config
, id
))) {
308 * Store after load dependency ordering the writes to
309 * the subbuffer after load and test of the noref flag
310 * matches the memory barrier implied by the cmpxchg()
311 * in update_read_sb_index().
313 return; /* Already writing to this buffer */
316 subbuffer_id_clear_noref(config
, &new_id
);
317 new_id
= cmpxchg(&bufb
->buf_wsb
[idx
].id
, id
, new_id
);
318 if (likely(new_id
== id
))
325 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
329 void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config
*config
,
330 struct lib_ring_buffer_backend
*bufb
,
331 unsigned long idx
, unsigned long offset
)
333 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
337 * Because ring_buffer_set_noref() is only called by a single thread
338 * (the one which updated the cc_sb value), there are no concurrent
339 * updates to take care of: other writers have not updated cc_sb, so
340 * they cannot set the noref flag, and concurrent readers cannot modify
341 * the pointer because the noref flag is not set yet.
342 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
343 * to the subbuffer before this set noref operation.
344 * subbuffer_set_noref() uses a volatile store to deal with concurrent
345 * readers of the noref flag.
347 CHAN_WARN_ON(bufb
->chan
,
348 subbuffer_id_is_noref(config
, bufb
->buf_wsb
[idx
].id
));
350 * Memory barrier that ensures counter stores are ordered before set
354 subbuffer_id_set_noref_offset(config
, &bufb
->buf_wsb
[idx
].id
, offset
);
358 * update_read_sb_index - Read-side subbuffer index update.
361 int update_read_sb_index(const struct lib_ring_buffer_config
*config
,
362 struct lib_ring_buffer_backend
*bufb
,
363 struct channel_backend
*chanb
,
364 unsigned long consumed_idx
,
365 unsigned long consumed_count
)
367 unsigned long old_id
, new_id
;
369 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
371 * Exchange the target writer subbuffer with our own unused
372 * subbuffer. No need to use ACCESS_ONCE() here to read the
373 * old_wpage, because the value read will be confirmed by the
374 * following cmpxchg().
376 old_id
= bufb
->buf_wsb
[consumed_idx
].id
;
377 if (unlikely(!subbuffer_id_is_noref(config
, old_id
)))
380 * Make sure the offset count we are expecting matches the one
381 * indicated by the writer.
383 if (unlikely(!subbuffer_id_compare_offset(config
, old_id
,
386 CHAN_WARN_ON(bufb
->chan
,
387 !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
388 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
390 new_id
= cmpxchg(&bufb
->buf_wsb
[consumed_idx
].id
, old_id
,
392 if (unlikely(old_id
!= new_id
))
394 bufb
->buf_rsb
.id
= new_id
;
396 /* No page exchange, use the writer page directly */
397 bufb
->buf_rsb
.id
= bufb
->buf_wsb
[consumed_idx
].id
;
403 * Use the architecture-specific memcpy implementation for constant-sized
404 * inputs, but rely on an inline memcpy for length statically unknown.
405 * The function call to memcpy is just way too expensive for a fast path.
407 #define lib_ring_buffer_do_copy(config, dest, src, len) \
409 size_t __len = (len); \
410 if (__builtin_constant_p(len)) \
411 memcpy(dest, src, __len); \
413 inline_memcpy(dest, src, __len); \
416 #endif /* _LINUX_RING_BUFFER_BACKEND_INTERNAL_H */