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 volatile uint32_t br_cons_head __aligned(CACHE_LINE_SIZE);
51 volatile uint32_t br_cons_tail;
57 void *br_ring[0] __aligned(CACHE_LINE_SIZE);
61 * multi-producer safe lock-free ring buffer enqueue
65 buf_ring_enqueue(struct buf_ring *br, void *buf)
67 uint32_t prod_head, prod_next;
71 for (i = br->br_cons_head; i != br->br_prod_head;
72 i = ((i + 1) & br->br_cons_mask))
73 if(br->br_ring[i] == buf)
74 panic("buf=%p already enqueue at %d prod=%d cons=%d",
75 buf, i, br->br_prod_tail, br->br_cons_tail);
79 prod_head = br->br_prod_head;
80 cons_tail = br->br_cons_tail;
82 prod_next = (prod_head + 1) & br->br_prod_mask;
84 if (prod_next == cons_tail) {
89 } while (!atomic_cmpset_int(&br->br_prod_head, prod_head, prod_next));
91 if (br->br_ring[prod_head] != NULL)
92 panic("dangling value in enqueue");
94 br->br_ring[prod_head] = buf;
97 * The full memory barrier also avoids that br_prod_tail store
98 * is reordered before the br_ring[prod_head] is full setup.
103 * If there are other enqueues in progress
104 * that preceeded us, we need to wait for them
107 while (br->br_prod_tail != prod_head)
109 br->br_prod_tail = prod_next;
115 * multi-consumer safe dequeue
118 static __inline void *
119 buf_ring_dequeue_mc(struct buf_ring *br)
121 uint32_t cons_head, cons_next;
128 cons_head = br->br_cons_head;
129 prod_tail = br->br_prod_tail;
131 cons_next = (cons_head + 1) & br->br_cons_mask;
133 if (cons_head == prod_tail) {
138 success = atomic_cmpset_int(&br->br_cons_head, cons_head,
140 } while (success == 0);
142 buf = br->br_ring[cons_head];
144 br->br_ring[cons_head] = NULL;
148 * The full memory barrier also avoids that br_ring[cons_read]
149 * load is reordered after br_cons_tail is set.
154 * If there are other dequeues in progress
155 * that preceeded us, we need to wait for them
158 while (br->br_cons_tail != cons_head)
161 br->br_cons_tail = cons_next;
168 * single-consumer dequeue
169 * use where dequeue is protected by a lock
170 * e.g. a network driver's tx queue lock
172 static __inline void *
173 buf_ring_dequeue_sc(struct buf_ring *br)
175 uint32_t cons_head, cons_next;
176 #ifdef PREFETCH_DEFINED
177 uint32_t cons_next_next;
182 cons_head = br->br_cons_head;
183 prod_tail = br->br_prod_tail;
185 cons_next = (cons_head + 1) & br->br_cons_mask;
186 #ifdef PREFETCH_DEFINED
187 cons_next_next = (cons_head + 2) & br->br_cons_mask;
190 if (cons_head == prod_tail)
193 #ifdef PREFETCH_DEFINED
194 if (cons_next != prod_tail) {
195 prefetch(br->br_ring[cons_next]);
196 if (cons_next_next != prod_tail)
197 prefetch(br->br_ring[cons_next_next]);
200 br->br_cons_head = cons_next;
201 buf = br->br_ring[cons_head];
204 br->br_ring[cons_head] = NULL;
205 if (!mtx_owned(br->br_lock))
206 panic("lock not held on single consumer dequeue");
207 if (br->br_cons_tail != cons_head)
208 panic("inconsistent list cons_tail=%d cons_head=%d",
209 br->br_cons_tail, cons_head);
211 br->br_cons_tail = cons_next;
216 * single-consumer advance after a peek
217 * use where it is protected by a lock
218 * e.g. a network driver's tx queue lock
221 buf_ring_advance_sc(struct buf_ring *br)
223 uint32_t cons_head, cons_next;
226 cons_head = br->br_cons_head;
227 prod_tail = br->br_prod_tail;
229 cons_next = (cons_head + 1) & br->br_cons_mask;
230 if (cons_head == prod_tail)
232 br->br_cons_head = cons_next;
234 br->br_ring[cons_head] = NULL;
236 br->br_cons_tail = cons_next;
240 * Used to return a buffer (most likely already there)
241 * to the top od the ring. The caller should *not*
242 * have used any dequeue to pull it out of the ring
243 * but instead should have used the peek() function.
244 * This is normally used where the transmit queue
245 * of a driver is full, and an mubf must be returned.
246 * Most likely whats in the ring-buffer is what
247 * is being put back (since it was not removed), but
248 * sometimes the lower transmit function may have
249 * done a pullup or other function that will have
250 * changed it. As an optimzation we always put it
251 * back (since jhb says the store is probably cheaper),
252 * if we have to do a multi-queue version we will need
253 * the compare and an atomic.
256 buf_ring_putback_sc(struct buf_ring *br, void *new)
258 KASSERT(br->br_cons_head != br->br_prod_tail,
259 ("Buf-Ring has none in putback")) ;
260 br->br_ring[br->br_cons_head] = new;
264 * return a pointer to the first entry in the ring
265 * without modifying it, or NULL if the ring is empty
266 * race-prone if not protected by a lock
268 static __inline void *
269 buf_ring_peek(struct buf_ring *br)
273 if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
274 panic("lock not held on single consumer dequeue");
277 * I believe it is safe to not have a memory barrier
278 * here because we control cons and tail is worst case
279 * a lagging indicator so we worst case we might
280 * return NULL immediately after a buffer has been enqueued
282 if (br->br_cons_head == br->br_prod_tail)
285 return (br->br_ring[br->br_cons_head]);
289 buf_ring_full(struct buf_ring *br)
292 return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
296 buf_ring_empty(struct buf_ring *br)
299 return (br->br_cons_head == br->br_prod_tail);
303 buf_ring_count(struct buf_ring *br)
306 return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
310 struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
312 void buf_ring_free(struct buf_ring *br, struct malloc_type *type);