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;
52 * Pad out to next L2 cache line
56 volatile uint32_t br_cons_head;
57 volatile uint32_t br_cons_tail;
62 * Pad out to next L2 cache line
72 * multi-producer safe lock-free ring buffer enqueue
76 buf_ring_enqueue(struct buf_ring *br, void *buf)
78 uint32_t prod_head, prod_next;
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);
91 prod_head = br->br_prod_head;
92 cons_tail = br->br_cons_tail;
94 prod_next = (prod_head + 1) & br->br_prod_mask;
96 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_tail = prod_next;
126 * multi-consumer safe dequeue
129 static __inline void *
130 buf_ring_dequeue_mc(struct buf_ring *br)
132 uint32_t cons_head, cons_next;
139 cons_head = br->br_cons_head;
140 prod_tail = br->br_prod_tail;
142 cons_next = (cons_head + 1) & br->br_cons_mask;
144 if (cons_head == prod_tail) {
149 success = atomic_cmpset_int(&br->br_cons_head, cons_head,
151 } while (success == 0);
153 buf = br->br_ring[cons_head];
155 br->br_ring[cons_head] = NULL;
160 * If there are other dequeues in progress
161 * that preceeded us, we need to wait for them
164 while (br->br_cons_tail != cons_head)
167 br->br_cons_tail = cons_next;
174 * single-consumer dequeue
175 * use where dequeue is protected by a lock
176 * e.g. a network driver's tx queue lock
178 static __inline void *
179 buf_ring_dequeue_sc(struct buf_ring *br)
181 uint32_t cons_head, cons_next, cons_next_next;
185 cons_head = br->br_cons_head;
186 prod_tail = br->br_prod_tail;
188 cons_next = (cons_head + 1) & br->br_cons_mask;
189 cons_next_next = (cons_head + 2) & br->br_cons_mask;
191 if (cons_head == prod_tail)
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]);
201 br->br_cons_head = cons_next;
202 buf = br->br_ring[cons_head];
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);
212 br->br_cons_tail = cons_next;
217 * return a pointer to the first entry in the ring
218 * without modifying it, or NULL if the ring is empty
219 * race-prone if not protected by a lock
221 static __inline void *
222 buf_ring_peek(struct buf_ring *br)
226 if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
227 panic("lock not held on single consumer dequeue");
230 * I believe it is safe to not have a memory barrier
231 * here because we control cons and tail is worst case
232 * a lagging indicator so we worst case we might
233 * return NULL immediately after a buffer has been enqueued
235 if (br->br_cons_head == br->br_prod_tail)
238 return (br->br_ring[br->br_cons_head]);
242 buf_ring_full(struct buf_ring *br)
245 return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
249 buf_ring_empty(struct buf_ring *br)
252 return (br->br_cons_head == br->br_prod_tail);
256 buf_ring_count(struct buf_ring *br)
259 return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
263 struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
265 void buf_ring_free(struct buf_ring *br, struct malloc_type *type);