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