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: releng/9.2/sys/sys/buf_ring.h 248287 2013-03-14 21:39:39Z jfv $
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 uint64_t br_prod_bufs;
51 /*
52 * Pad out to next L2 cache line
53 */
54 uint64_t _pad0[11];
55
56 volatile uint32_t br_cons_head;
57 volatile uint32_t br_cons_tail;
58 int br_cons_size;
59 int br_cons_mask;
60
61 /*
62 * Pad out to next L2 cache line
63 */
64 uint64_t _pad1[14];
65 #ifdef DEBUG_BUFRING
66 struct mtx *br_lock;
67 #endif
68 void *br_ring[0];
69 };
70
71 /*
72 * multi-producer safe lock-free ring buffer enqueue
73 *
74 */
75 static __inline int
76 buf_ring_enqueue(struct buf_ring *br, void *buf)
77 {
78 uint32_t prod_head, prod_next;
79 uint32_t cons_tail;
80 int success;
81 #ifdef DEBUG_BUFRING
82 int i;
83 for (i = br->br_cons_head; i != br->br_prod_head;
84 i = ((i + 1) & br->br_cons_mask))
85 if(br->br_ring[i] == buf)
86 panic("buf=%p already enqueue at %d prod=%d cons=%d",
87 buf, i, br->br_prod_tail, br->br_cons_tail);
88 #endif
89 critical_enter();
90 do {
91 prod_head = br->br_prod_head;
92 cons_tail = br->br_cons_tail;
93
94 prod_next = (prod_head + 1) & br->br_prod_mask;
95
96 if (prod_next == cons_tail) {
97 br->br_drops++;
98 critical_exit();
99 return (ENOBUFS);
100 }
101
102 success = atomic_cmpset_int(&br->br_prod_head, prod_head,
103 prod_next);
104 } while (success == 0);
105 #ifdef DEBUG_BUFRING
106 if (br->br_ring[prod_head] != NULL)
107 panic("dangling value in enqueue");
108 #endif
109 br->br_ring[prod_head] = buf;
110 wmb();
111
112 /*
113 * If there are other enqueues in progress
114 * that preceeded us, we need to wait for them
115 * to complete
116 */
117 while (br->br_prod_tail != prod_head)
118 cpu_spinwait();
119 br->br_prod_bufs++;
120 br->br_prod_tail = prod_next;
121 critical_exit();
122 return (0);
123 }
124
125 /*
126 * multi-consumer safe dequeue
127 *
128 */
129 static __inline void *
130 buf_ring_dequeue_mc(struct buf_ring *br)
131 {
132 uint32_t cons_head, cons_next;
133 uint32_t prod_tail;
134 void *buf;
135 int success;
136
137 critical_enter();
138 do {
139 cons_head = br->br_cons_head;
140 prod_tail = br->br_prod_tail;
141
142 cons_next = (cons_head + 1) & br->br_cons_mask;
143
144 if (cons_head == prod_tail) {
145 critical_exit();
146 return (NULL);
147 }
148
149 success = atomic_cmpset_int(&br->br_cons_head, cons_head,
150 cons_next);
151 } while (success == 0);
152
153 buf = br->br_ring[cons_head];
154 #ifdef DEBUG_BUFRING
155 br->br_ring[cons_head] = NULL;
156 #endif
157 rmb();
158
159 /*
160 * If there are other dequeues in progress
161 * that preceeded us, we need to wait for them
162 * to complete
163 */
164 while (br->br_cons_tail != cons_head)
165 cpu_spinwait();
166
167 br->br_cons_tail = cons_next;
168 critical_exit();
169
170 return (buf);
171 }
172
173 /*
174 * single-consumer dequeue
175 * use where dequeue is protected by a lock
176 * e.g. a network driver's tx queue lock
177 */
178 static __inline void *
179 buf_ring_dequeue_sc(struct buf_ring *br)
180 {
181 uint32_t cons_head, cons_next, cons_next_next;
182 uint32_t prod_tail;
183 void *buf;
184
185 cons_head = br->br_cons_head;
186 prod_tail = br->br_prod_tail;
187
188 cons_next = (cons_head + 1) & br->br_cons_mask;
189 cons_next_next = (cons_head + 2) & br->br_cons_mask;
190
191 if (cons_head == prod_tail)
192 return (NULL);
193
194 #ifdef PREFETCH_DEFINED
195 if (cons_next != prod_tail) {
196 prefetch(br->br_ring[cons_next]);
197 if (cons_next_next != prod_tail)
198 prefetch(br->br_ring[cons_next_next]);
199 }
200 #endif
201 br->br_cons_head = cons_next;
202 buf = br->br_ring[cons_head];
203
204 #ifdef DEBUG_BUFRING
205 br->br_ring[cons_head] = NULL;
206 if (!mtx_owned(br->br_lock))
207 panic("lock not held on single consumer dequeue");
208 if (br->br_cons_tail != cons_head)
209 panic("inconsistent list cons_tail=%d cons_head=%d",
210 br->br_cons_tail, cons_head);
211 #endif
212 br->br_cons_tail = cons_next;
213 return (buf);
214 }
215
216 /*
217 * single-consumer advance after a peek
218 * use where it is protected by a lock
219 * e.g. a network driver's tx queue lock
220 */
221 static __inline void
222 buf_ring_advance_sc(struct buf_ring *br)
223 {
224 uint32_t cons_head, cons_next;
225 uint32_t prod_tail;
226
227 cons_head = br->br_cons_head;
228 prod_tail = br->br_prod_tail;
229
230 cons_next = (cons_head + 1) & br->br_cons_mask;
231 if (cons_head == prod_tail)
232 return;
233 br->br_cons_head = cons_next;
234 #ifdef DEBUG_BUFRING
235 br->br_ring[cons_head] = NULL;
236 #endif
237 br->br_cons_tail = cons_next;
238 }
239
240 /*
241 * Used to return a buffer (most likely already there)
242 * to the top od the ring. The caller should *not*
243 * have used any dequeue to pull it out of the ring
244 * but instead should have used the peek() function.
245 * This is normally used where the transmit queue
246 * of a driver is full, and an mubf must be returned.
247 * Most likely whats in the ring-buffer is what
248 * is being put back (since it was not removed), but
249 * sometimes the lower transmit function may have
250 * done a pullup or other function that will have
251 * changed it. As an optimzation we always put it
252 * back (since jhb says the store is probably cheaper),
253 * if we have to do a multi-queue version we will need
254 * the compare and an atomic.
255 */
256 static __inline void
257 buf_ring_putback_sc(struct buf_ring *br, void *new)
258 {
259 KASSERT(br->br_cons_head != br->br_prod_tail,
260 ("Buf-Ring has none in putback")) ;
261 br->br_ring[br->br_cons_head] = new;
262 }
263
264 /*
265 * return a pointer to the first entry in the ring
266 * without modifying it, or NULL if the ring is empty
267 * race-prone if not protected by a lock
268 */
269 static __inline void *
270 buf_ring_peek(struct buf_ring *br)
271 {
272
273 #ifdef DEBUG_BUFRING
274 if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
275 panic("lock not held on single consumer dequeue");
276 #endif
277 /*
278 * I believe it is safe to not have a memory barrier
279 * here because we control cons and tail is worst case
280 * a lagging indicator so we worst case we might
281 * return NULL immediately after a buffer has been enqueued
282 */
283 if (br->br_cons_head == br->br_prod_tail)
284 return (NULL);
285
286 return (br->br_ring[br->br_cons_head]);
287 }
288
289 static __inline int
290 buf_ring_full(struct buf_ring *br)
291 {
292
293 return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
294 }
295
296 static __inline int
297 buf_ring_empty(struct buf_ring *br)
298 {
299
300 return (br->br_cons_head == br->br_prod_tail);
301 }
302
303 static __inline int
304 buf_ring_count(struct buf_ring *br)
305 {
306
307 return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
308 & br->br_prod_mask);
309 }
310
311 struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
312 struct mtx *);
313 void buf_ring_free(struct buf_ring *br, struct malloc_type *type);
314
315
316
317 #endif
Cache object: b41b0f5f0caa7dc48d3b090ad7ea90d1
|