FreeBSD/Linux Kernel Cross Reference
sys/sys/buf_ring.h
1 /*-
2 * Copyright (c) 2007-2009 Kip Macy <kmacy@freebsd.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD$
27 *
28 */
29
30 #ifndef _SYS_BUF_RING_H_
31 #define _SYS_BUF_RING_H_
32
33 #include <machine/cpu.h>
34
35 #if defined(INVARIANTS) && !defined(DEBUG_BUFRING)
36 #define DEBUG_BUFRING 1
37 #endif
38
39 #ifdef DEBUG_BUFRING
40 #include <sys/lock.h>
41 #include <sys/mutex.h>
42 #endif
43
44 struct buf_ring {
45 volatile uint32_t br_prod_head;
46 volatile uint32_t br_prod_tail;
47 int br_prod_size;
48 int br_prod_mask;
49 uint64_t br_drops;
50 volatile uint32_t br_cons_head __aligned(CACHE_LINE_SIZE);
51 volatile uint32_t br_cons_tail;
52 int br_cons_size;
53 int br_cons_mask;
54 #ifdef DEBUG_BUFRING
55 struct mtx *br_lock;
56 #endif
57 void *br_ring[0] __aligned(CACHE_LINE_SIZE);
58 };
59
60 /*
61 * multi-producer safe lock-free ring buffer enqueue
62 *
63 */
64 static __inline int
65 buf_ring_enqueue(struct buf_ring *br, void *buf)
66 {
67 uint32_t prod_head, prod_next, cons_tail;
68 #ifdef DEBUG_BUFRING
69 int i;
70 for (i = br->br_cons_head; i != br->br_prod_head;
71 i = ((i + 1) & br->br_cons_mask))
72 if(br->br_ring[i] == buf)
73 panic("buf=%p already enqueue at %d prod=%d cons=%d",
74 buf, i, br->br_prod_tail, br->br_cons_tail);
75 #endif
76 critical_enter();
77 do {
78 prod_head = br->br_prod_head;
79 prod_next = (prod_head + 1) & br->br_prod_mask;
80 cons_tail = br->br_cons_tail;
81
82 if (prod_next == cons_tail) {
83 rmb();
84 if (prod_head == br->br_prod_head &&
85 cons_tail == br->br_cons_tail) {
86 br->br_drops++;
87 critical_exit();
88 return (ENOBUFS);
89 }
90 continue;
91 }
92 } while (!atomic_cmpset_acq_int(&br->br_prod_head, prod_head, prod_next));
93 #ifdef DEBUG_BUFRING
94 if (br->br_ring[prod_head] != NULL)
95 panic("dangling value in enqueue");
96 #endif
97 br->br_ring[prod_head] = buf;
98
99 /*
100 * If there are other enqueues in progress
101 * that preceded us, we need to wait for them
102 * to complete
103 */
104 while (br->br_prod_tail != prod_head)
105 cpu_spinwait();
106 atomic_store_rel_int(&br->br_prod_tail, prod_next);
107 critical_exit();
108 return (0);
109 }
110
111 /*
112 * multi-consumer safe dequeue
113 *
114 */
115 static __inline void *
116 buf_ring_dequeue_mc(struct buf_ring *br)
117 {
118 uint32_t cons_head, cons_next;
119 void *buf;
120
121 critical_enter();
122 do {
123 cons_head = br->br_cons_head;
124 cons_next = (cons_head + 1) & br->br_cons_mask;
125
126 if (cons_head == br->br_prod_tail) {
127 critical_exit();
128 return (NULL);
129 }
130 } while (!atomic_cmpset_acq_int(&br->br_cons_head, cons_head, cons_next));
131
132 buf = br->br_ring[cons_head];
133 #ifdef DEBUG_BUFRING
134 br->br_ring[cons_head] = NULL;
135 #endif
136 /*
137 * If there are other dequeues in progress
138 * that preceded us, we need to wait for them
139 * to complete
140 */
141 while (br->br_cons_tail != cons_head)
142 cpu_spinwait();
143
144 atomic_store_rel_int(&br->br_cons_tail, cons_next);
145 critical_exit();
146
147 return (buf);
148 }
149
150 /*
151 * single-consumer dequeue
152 * use where dequeue is protected by a lock
153 * e.g. a network driver's tx queue lock
154 */
155 static __inline void *
156 buf_ring_dequeue_sc(struct buf_ring *br)
157 {
158 uint32_t cons_head, cons_next, cons_next_next;
159 uint32_t prod_tail;
160 void *buf;
161
162 cons_head = br->br_cons_head;
163 prod_tail = br->br_prod_tail;
164
165 cons_next = (cons_head + 1) & br->br_cons_mask;
166 cons_next_next = (cons_head + 2) & br->br_cons_mask;
167
168 if (cons_head == prod_tail)
169 return (NULL);
170
171 #ifdef PREFETCH_DEFINED
172 if (cons_next != prod_tail) {
173 prefetch(br->br_ring[cons_next]);
174 if (cons_next_next != prod_tail)
175 prefetch(br->br_ring[cons_next_next]);
176 }
177 #endif
178 br->br_cons_head = cons_next;
179 buf = br->br_ring[cons_head];
180
181 #ifdef DEBUG_BUFRING
182 br->br_ring[cons_head] = NULL;
183 if (!mtx_owned(br->br_lock))
184 panic("lock not held on single consumer dequeue");
185 if (br->br_cons_tail != cons_head)
186 panic("inconsistent list cons_tail=%d cons_head=%d",
187 br->br_cons_tail, cons_head);
188 #endif
189 br->br_cons_tail = cons_next;
190 return (buf);
191 }
192
193 /*
194 * single-consumer advance after a peek
195 * use where it is protected by a lock
196 * e.g. a network driver's tx queue lock
197 */
198 static __inline void
199 buf_ring_advance_sc(struct buf_ring *br)
200 {
201 uint32_t cons_head, cons_next;
202 uint32_t prod_tail;
203
204 cons_head = br->br_cons_head;
205 prod_tail = br->br_prod_tail;
206
207 cons_next = (cons_head + 1) & br->br_cons_mask;
208 if (cons_head == prod_tail)
209 return;
210 br->br_cons_head = cons_next;
211 #ifdef DEBUG_BUFRING
212 br->br_ring[cons_head] = NULL;
213 #endif
214 br->br_cons_tail = cons_next;
215 }
216
217 /*
218 * Used to return a buffer (most likely already there)
219 * to the top od the ring. The caller should *not*
220 * have used any dequeue to pull it out of the ring
221 * but instead should have used the peek() function.
222 * This is normally used where the transmit queue
223 * of a driver is full, and an mubf must be returned.
224 * Most likely whats in the ring-buffer is what
225 * is being put back (since it was not removed), but
226 * sometimes the lower transmit function may have
227 * done a pullup or other function that will have
228 * changed it. As an optimzation we always put it
229 * back (since jhb says the store is probably cheaper),
230 * if we have to do a multi-queue version we will need
231 * the compare and an atomic.
232 */
233 static __inline void
234 buf_ring_putback_sc(struct buf_ring *br, void *new)
235 {
236 KASSERT(br->br_cons_head != br->br_prod_tail,
237 ("Buf-Ring has none in putback")) ;
238 br->br_ring[br->br_cons_head] = new;
239 }
240
241 /*
242 * return a pointer to the first entry in the ring
243 * without modifying it, or NULL if the ring is empty
244 * race-prone if not protected by a lock
245 */
246 static __inline void *
247 buf_ring_peek(struct buf_ring *br)
248 {
249
250 #ifdef DEBUG_BUFRING
251 if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
252 panic("lock not held on single consumer dequeue");
253 #endif
254 /*
255 * I believe it is safe to not have a memory barrier
256 * here because we control cons and tail is worst case
257 * a lagging indicator so we worst case we might
258 * return NULL immediately after a buffer has been enqueued
259 */
260 if (br->br_cons_head == br->br_prod_tail)
261 return (NULL);
262
263 return (br->br_ring[br->br_cons_head]);
264 }
265
266 static __inline void *
267 buf_ring_peek_clear_sc(struct buf_ring *br)
268 {
269 #ifdef DEBUG_BUFRING
270 void *ret;
271
272 if (!mtx_owned(br->br_lock))
273 panic("lock not held on single consumer dequeue");
274 #endif
275 /*
276 * I believe it is safe to not have a memory barrier
277 * here because we control cons and tail is worst case
278 * a lagging indicator so we worst case we might
279 * return NULL immediately after a buffer has been enqueued
280 */
281 if (br->br_cons_head == br->br_prod_tail)
282 return (NULL);
283
284 #ifdef DEBUG_BUFRING
285 /*
286 * Single consumer, i.e. cons_head will not move while we are
287 * running, so atomic_swap_ptr() is not necessary here.
288 */
289 ret = br->br_ring[br->br_cons_head];
290 br->br_ring[br->br_cons_head] = NULL;
291 return (ret);
292 #else
293 return (br->br_ring[br->br_cons_head]);
294 #endif
295 }
296
297 static __inline int
298 buf_ring_full(struct buf_ring *br)
299 {
300
301 return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
302 }
303
304 static __inline int
305 buf_ring_empty(struct buf_ring *br)
306 {
307
308 return (br->br_cons_head == br->br_prod_tail);
309 }
310
311 static __inline int
312 buf_ring_count(struct buf_ring *br)
313 {
314
315 return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
316 & br->br_prod_mask);
317 }
318
319 struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
320 struct mtx *);
321 void buf_ring_free(struct buf_ring *br, struct malloc_type *type);
322
323
324
325 #endif
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