buf_ring.h revision 244732
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: head/sys/sys/buf_ring.h 244732 2012-12-27 12:36:58Z attilio $ 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 uint64_t br_prod_bufs; 51 /* 52 * Pad out to next L2 cache line 53 */ 54 uint64_t _pad0[11]; 55 56 volatile uint32_t br_cons_head; 57 volatile uint32_t br_cons_tail; 58 int br_cons_size; 59 int br_cons_mask; 60 61 /* 62 * Pad out to next L2 cache line 63 */ 64 uint64_t _pad1[14]; 65#ifdef DEBUG_BUFRING 66 struct mtx *br_lock; 67#endif 68 void *br_ring[0]; 69}; 70 71/* 72 * multi-producer safe lock-free ring buffer enqueue 73 * 74 */ 75static __inline int 76buf_ring_enqueue(struct buf_ring *br, void *buf) 77{ 78 uint32_t prod_head, prod_next; 79 uint32_t cons_tail; 80 int success; 81#ifdef DEBUG_BUFRING 82 int i; 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); 88#endif 89 critical_enter(); 90 do { 91 prod_head = br->br_prod_head; 92 cons_tail = br->br_cons_tail; 93 94 prod_next = (prod_head + 1) & br->br_prod_mask; 95 96 if (prod_next == cons_tail) { 97 br->br_drops++; 98 critical_exit(); 99 return (ENOBUFS); 100 } 101 102 success = atomic_cmpset_int(&br->br_prod_head, prod_head, 103 prod_next); 104 } while (success == 0); 105#ifdef DEBUG_BUFRING 106 if (br->br_ring[prod_head] != NULL) 107 panic("dangling value in enqueue"); 108#endif 109 br->br_ring[prod_head] = buf; 110 wmb(); 111 112 /* 113 * If there are other enqueues in progress 114 * that preceeded us, we need to wait for them 115 * to complete 116 */ 117 while (atomic_load_acq_32(&br->br_prod_tail) != prod_head) 118 cpu_spinwait(); 119 br->br_prod_bufs++; 120 atomic_store_rel_32(&br->br_prod_tail, prod_next); 121 critical_exit(); 122 return (0); 123} 124 125/* 126 * multi-consumer safe dequeue 127 * 128 */ 129static __inline void * 130buf_ring_dequeue_mc(struct buf_ring *br) 131{ 132 uint32_t cons_head, cons_next; 133 uint32_t prod_tail; 134 void *buf; 135 int success; 136 137 critical_enter(); 138 do { 139 cons_head = br->br_cons_head; 140 prod_tail = br->br_prod_tail; 141 142 cons_next = (cons_head + 1) & br->br_cons_mask; 143 144 if (cons_head == prod_tail) { 145 critical_exit(); 146 return (NULL); 147 } 148 149 success = atomic_cmpset_int(&br->br_cons_head, cons_head, 150 cons_next); 151 } while (success == 0); 152 153 buf = br->br_ring[cons_head]; 154#ifdef DEBUG_BUFRING 155 br->br_ring[cons_head] = NULL; 156#endif 157 rmb(); 158 159 /* 160 * If there are other dequeues in progress 161 * that preceeded us, we need to wait for them 162 * to complete 163 */ 164 while (atomic_load_acq_32(&br->br_cons_tail) != cons_head) 165 cpu_spinwait(); 166 167 atomic_store_rel_32(&br->br_cons_tail, cons_next); 168 critical_exit(); 169 170 return (buf); 171} 172 173/* 174 * single-consumer dequeue 175 * use where dequeue is protected by a lock 176 * e.g. a network driver's tx queue lock 177 */ 178static __inline void * 179buf_ring_dequeue_sc(struct buf_ring *br) 180{ 181 uint32_t cons_head, cons_next, cons_next_next; 182 uint32_t prod_tail; 183 void *buf; 184 185 cons_head = br->br_cons_head; 186 prod_tail = br->br_prod_tail; 187 188 cons_next = (cons_head + 1) & br->br_cons_mask; 189 cons_next_next = (cons_head + 2) & br->br_cons_mask; 190 191 if (cons_head == prod_tail) 192 return (NULL); 193 194#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]); 199 } 200#endif 201 br->br_cons_head = cons_next; 202 buf = br->br_ring[cons_head]; 203 204#ifdef DEBUG_BUFRING 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); 211#endif 212 atomic_store_rel_32(&br->br_cons_tail, cons_next); 213 return (buf); 214} 215 216/* 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 220 */ 221static __inline void * 222buf_ring_peek(struct buf_ring *br) 223{ 224 225#ifdef DEBUG_BUFRING 226 if ((br->br_lock != NULL) && !mtx_owned(br->br_lock)) 227 panic("lock not held on single consumer dequeue"); 228#endif 229 /* 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 234 */ 235 if (br->br_cons_head == br->br_prod_tail) 236 return (NULL); 237 238 return (br->br_ring[br->br_cons_head]); 239} 240 241static __inline int 242buf_ring_full(struct buf_ring *br) 243{ 244 245 return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail); 246} 247 248static __inline int 249buf_ring_empty(struct buf_ring *br) 250{ 251 252 return (br->br_cons_head == br->br_prod_tail); 253} 254 255static __inline int 256buf_ring_count(struct buf_ring *br) 257{ 258 259 return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail) 260 & br->br_prod_mask); 261} 262 263struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags, 264 struct mtx *); 265void buf_ring_free(struct buf_ring *br, struct malloc_type *type); 266 267 268 269#endif 270