2 * Copyright (c) 2007-2009 Kip Macy <kmacy@freebsd.org>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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
30 #ifndef _SYS_BUF_RING_H_
31 #define _SYS_BUF_RING_H_
33 #include <machine/cpu.h>
35 #if defined(INVARIANTS) && !defined(DEBUG_BUFRING)
36 #define DEBUG_BUFRING 1
41 #include <sys/mutex.h>
45 volatile uint32_t br_prod_head;
46 volatile uint32_t br_prod_tail;
50 uint64_t br_prod_bufs;
51 uint64_t br_prod_bytes;
53 * Pad out to next L2 cache line
57 volatile uint32_t br_cons_head;
58 volatile uint32_t br_cons_tail;
63 * Pad out to next L2 cache line
73 * multi-producer safe lock-free ring buffer enqueue
77 buf_ring_enqueue_bytes(struct buf_ring *br, void *buf, int nbytes)
79 uint32_t prod_head, prod_next;
84 for (i = br->br_cons_head; i != br->br_prod_head;
85 i = ((i + 1) & br->br_cons_mask))
86 if(br->br_ring[i] == buf)
87 panic("buf=%p already enqueue at %d prod=%d cons=%d",
88 buf, i, br->br_prod_tail, br->br_cons_tail);
92 prod_head = br->br_prod_head;
93 cons_tail = br->br_cons_tail;
95 prod_next = (prod_head + 1) & br->br_prod_mask;
97 if (prod_next == cons_tail) {
102 success = atomic_cmpset_int(&br->br_prod_head, prod_head,
104 } while (success == 0);
106 if (br->br_ring[prod_head] != NULL)
107 panic("dangling value in enqueue");
109 br->br_ring[prod_head] = buf;
113 * If there are other enqueues in progress
114 * that preceeded us, we need to wait for them
117 while (br->br_prod_tail != prod_head)
120 br->br_prod_bytes += nbytes;
121 br->br_prod_tail = prod_next;
127 buf_ring_enqueue(struct buf_ring *br, void *buf)
130 return (buf_ring_enqueue_bytes(br, buf, 0));
134 * multi-consumer safe dequeue
137 static __inline void *
138 buf_ring_dequeue_mc(struct buf_ring *br)
140 uint32_t cons_head, cons_next;
147 cons_head = br->br_cons_head;
148 prod_tail = br->br_prod_tail;
150 cons_next = (cons_head + 1) & br->br_cons_mask;
152 if (cons_head == prod_tail) {
157 success = atomic_cmpset_int(&br->br_cons_head, cons_head,
159 } while (success == 0);
161 buf = br->br_ring[cons_head];
163 br->br_ring[cons_head] = NULL;
168 * If there are other dequeues in progress
169 * that preceeded us, we need to wait for them
172 while (br->br_cons_tail != cons_head)
175 br->br_cons_tail = cons_next;
182 * single-consumer dequeue
183 * use where dequeue is protected by a lock
184 * e.g. a network driver's tx queue lock
186 static __inline void *
187 buf_ring_dequeue_sc(struct buf_ring *br)
189 uint32_t cons_head, cons_next, cons_next_next;
193 cons_head = br->br_cons_head;
194 prod_tail = br->br_prod_tail;
196 cons_next = (cons_head + 1) & br->br_cons_mask;
197 cons_next_next = (cons_head + 2) & br->br_cons_mask;
199 if (cons_head == prod_tail)
202 #ifdef PREFETCH_DEFINED
203 if (cons_next != prod_tail) {
204 prefetch(br->br_ring[cons_next]);
205 if (cons_next_next != prod_tail)
206 prefetch(br->br_ring[cons_next_next]);
209 br->br_cons_head = cons_next;
210 buf = br->br_ring[cons_head];
213 br->br_ring[cons_head] = NULL;
214 if (!mtx_owned(br->br_lock))
215 panic("lock not held on single consumer dequeue");
216 if (br->br_cons_tail != cons_head)
217 panic("inconsistent list cons_tail=%d cons_head=%d",
218 br->br_cons_tail, cons_head);
220 br->br_cons_tail = cons_next;
225 * return a pointer to the first entry in the ring
226 * without modifying it, or NULL if the ring is empty
227 * race-prone if not protected by a lock
229 static __inline void *
230 buf_ring_peek(struct buf_ring *br)
234 if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
235 panic("lock not held on single consumer dequeue");
238 * I believe it is safe to not have a memory barrier
239 * here because we control cons and tail is worst case
240 * a lagging indicator so we worst case we might
241 * return NULL immediately after a buffer has been enqueued
243 if (br->br_cons_head == br->br_prod_tail)
246 return (br->br_ring[br->br_cons_head]);
250 buf_ring_full(struct buf_ring *br)
253 return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
257 buf_ring_empty(struct buf_ring *br)
260 return (br->br_cons_head == br->br_prod_tail);
264 buf_ring_count(struct buf_ring *br)
267 return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
271 struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
273 void buf_ring_free(struct buf_ring *br, struct malloc_type *type);