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
44struct 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 */
64static __inline int
65buf_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 preceeded 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 */
115static __inline void *
116buf_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 preceeded 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 */
155static __inline void *
156buf_ring_dequeue_sc(struct buf_ring *br)
157{
158	uint32_t cons_head, cons_next;
159#ifdef PREFETCH_DEFINED
160	uint32_t cons_next_next;
161#endif
162	uint32_t prod_tail;
163	void *buf;
164
165	cons_head = br->br_cons_head;
166	prod_tail = br->br_prod_tail;
167
168	cons_next = (cons_head + 1) & br->br_cons_mask;
169#ifdef PREFETCH_DEFINED
170	cons_next_next = (cons_head + 2) & br->br_cons_mask;
171#endif
172
173	if (cons_head == prod_tail)
174		return (NULL);
175
176#ifdef PREFETCH_DEFINED
177	if (cons_next != prod_tail) {
178		prefetch(br->br_ring[cons_next]);
179		if (cons_next_next != prod_tail)
180			prefetch(br->br_ring[cons_next_next]);
181	}
182#endif
183	br->br_cons_head = cons_next;
184	buf = br->br_ring[cons_head];
185
186#ifdef DEBUG_BUFRING
187	br->br_ring[cons_head] = NULL;
188	if (!mtx_owned(br->br_lock))
189		panic("lock not held on single consumer dequeue");
190	if (br->br_cons_tail != cons_head)
191		panic("inconsistent list cons_tail=%d cons_head=%d",
192		    br->br_cons_tail, cons_head);
193#endif
194	br->br_cons_tail = cons_next;
195	return (buf);
196}
197
198/*
199 * single-consumer advance after a peek
200 * use where it is protected by a lock
201 * e.g. a network driver's tx queue lock
202 */
203static __inline void
204buf_ring_advance_sc(struct buf_ring *br)
205{
206	uint32_t cons_head, cons_next;
207	uint32_t prod_tail;
208
209	cons_head = br->br_cons_head;
210	prod_tail = br->br_prod_tail;
211
212	cons_next = (cons_head + 1) & br->br_cons_mask;
213	if (cons_head == prod_tail)
214		return;
215	br->br_cons_head = cons_next;
216#ifdef DEBUG_BUFRING
217	br->br_ring[cons_head] = NULL;
218#endif
219	br->br_cons_tail = cons_next;
220}
221
222/*
223 * Used to return a buffer (most likely already there)
224 * to the top od the ring. The caller should *not*
225 * have used any dequeue to pull it out of the ring
226 * but instead should have used the peek() function.
227 * This is normally used where the transmit queue
228 * of a driver is full, and an mubf must be returned.
229 * Most likely whats in the ring-buffer is what
230 * is being put back (since it was not removed), but
231 * sometimes the lower transmit function may have
232 * done a pullup or other function that will have
233 * changed it. As an optimzation we always put it
234 * back (since jhb says the store is probably cheaper),
235 * if we have to do a multi-queue version we will need
236 * the compare and an atomic.
237 */
238static __inline void
239buf_ring_putback_sc(struct buf_ring *br, void *new)
240{
241	KASSERT(br->br_cons_head != br->br_prod_tail,
242		("Buf-Ring has none in putback")) ;
243	br->br_ring[br->br_cons_head] = new;
244}
245
246/*
247 * return a pointer to the first entry in the ring
248 * without modifying it, or NULL if the ring is empty
249 * race-prone if not protected by a lock
250 */
251static __inline void *
252buf_ring_peek(struct buf_ring *br)
253{
254
255#ifdef DEBUG_BUFRING
256	if ((br->br_lock != NULL) && !mtx_owned(br->br_lock))
257		panic("lock not held on single consumer dequeue");
258#endif
259	/*
260	 * I believe it is safe to not have a memory barrier
261	 * here because we control cons and tail is worst case
262	 * a lagging indicator so we worst case we might
263	 * return NULL immediately after a buffer has been enqueued
264	 */
265	if (br->br_cons_head == br->br_prod_tail)
266		return (NULL);
267
268	return (br->br_ring[br->br_cons_head]);
269}
270
271static __inline int
272buf_ring_full(struct buf_ring *br)
273{
274
275	return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail);
276}
277
278static __inline int
279buf_ring_empty(struct buf_ring *br)
280{
281
282	return (br->br_cons_head == br->br_prod_tail);
283}
284
285static __inline int
286buf_ring_count(struct buf_ring *br)
287{
288
289	return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail)
290	    & br->br_prod_mask);
291}
292
293struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags,
294    struct mtx *);
295void buf_ring_free(struct buf_ring *br, struct malloc_type *type);
296
297
298
299#endif
300