subr_pserialize.c revision 1.5.8.2
1 /* $NetBSD: subr_pserialize.c,v 1.5.8.2 2013/02/11 20:42:50 riz Exp $ */ 2 3 /*- 4 * Copyright (c) 2010, 2011 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 19 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 26 * POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29 /* 30 * Passive serialization. 31 * 32 * Implementation accurately matches the lapsed US patent 4809168, therefore 33 * code is patent-free in the United States. Your use of this code is at 34 * your own risk. 35 * 36 * Note for NetBSD developers: all changes to this source file must be 37 * approved by the <core>. 38 */ 39 40 #include <sys/cdefs.h> 41 __KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.5.8.2 2013/02/11 20:42:50 riz Exp $"); 42 43 #include <sys/param.h> 44 45 #include <sys/condvar.h> 46 #include <sys/cpu.h> 47 #include <sys/evcnt.h> 48 #include <sys/kmem.h> 49 #include <sys/mutex.h> 50 #include <sys/pserialize.h> 51 #include <sys/proc.h> 52 #include <sys/queue.h> 53 #include <sys/xcall.h> 54 55 struct pserialize { 56 TAILQ_ENTRY(pserialize) psz_chain; 57 lwp_t * psz_owner; 58 kcpuset_t * psz_target; 59 kcpuset_t * psz_pass; 60 }; 61 62 static u_int psz_work_todo __cacheline_aligned; 63 static kmutex_t psz_lock __cacheline_aligned; 64 static struct evcnt psz_ev_excl __cacheline_aligned; 65 66 /* 67 * As defined in "Method 1": 68 * q0: "0 MP checkpoints have occured". 69 * q1: "1 MP checkpoint has occured". 70 * q2: "2 MP checkpoints have occured". 71 */ 72 static TAILQ_HEAD(, pserialize) psz_queue0 __cacheline_aligned; 73 static TAILQ_HEAD(, pserialize) psz_queue1 __cacheline_aligned; 74 static TAILQ_HEAD(, pserialize) psz_queue2 __cacheline_aligned; 75 76 /* 77 * pserialize_init: 78 * 79 * Initialize passive serialization structures. 80 */ 81 void 82 pserialize_init(void) 83 { 84 85 psz_work_todo = 0; 86 TAILQ_INIT(&psz_queue0); 87 TAILQ_INIT(&psz_queue1); 88 TAILQ_INIT(&psz_queue2); 89 mutex_init(&psz_lock, MUTEX_DEFAULT, IPL_SCHED); 90 evcnt_attach_dynamic(&psz_ev_excl, EVCNT_TYPE_MISC, NULL, 91 "pserialize", "exclusive access"); 92 } 93 94 /* 95 * pserialize_create: 96 * 97 * Create and initialize a passive serialization object. 98 */ 99 pserialize_t 100 pserialize_create(void) 101 { 102 pserialize_t psz; 103 104 psz = kmem_zalloc(sizeof(struct pserialize), KM_SLEEP); 105 kcpuset_create(&psz->psz_target, true); 106 kcpuset_create(&psz->psz_pass, true); 107 psz->psz_owner = NULL; 108 109 return psz; 110 } 111 112 /* 113 * pserialize_destroy: 114 * 115 * Destroy a passive serialization object. 116 */ 117 void 118 pserialize_destroy(pserialize_t psz) 119 { 120 121 KASSERT(psz->psz_owner == NULL); 122 123 kcpuset_destroy(psz->psz_target); 124 kcpuset_destroy(psz->psz_pass); 125 kmem_free(psz, sizeof(struct pserialize)); 126 } 127 128 /* 129 * pserialize_perform: 130 * 131 * Perform the write side of passive serialization. The calling 132 * thread holds an exclusive lock on the data object(s) being updated. 133 * We wait until every processor in the system has made at least two 134 * passes through cpu_swichto(). The wait is made with the caller's 135 * update lock held, but is short term. 136 */ 137 void 138 pserialize_perform(pserialize_t psz) 139 { 140 uint64_t xc; 141 142 KASSERT(!cpu_intr_p()); 143 KASSERT(!cpu_softintr_p()); 144 145 if (__predict_false(panicstr != NULL)) { 146 return; 147 } 148 KASSERT(psz->psz_owner == NULL); 149 KASSERT(ncpu > 0); 150 151 /* 152 * Set up the object and put it onto the queue. The lock 153 * activity here provides the necessary memory barrier to 154 * make the caller's data update completely visible to 155 * other processors. 156 */ 157 psz->psz_owner = curlwp; 158 kcpuset_copy(psz->psz_target, kcpuset_running); 159 kcpuset_zero(psz->psz_pass); 160 161 mutex_spin_enter(&psz_lock); 162 TAILQ_INSERT_TAIL(&psz_queue0, psz, psz_chain); 163 psz_work_todo++; 164 165 do { 166 mutex_spin_exit(&psz_lock); 167 168 /* 169 * Force some context switch activity on every CPU, as 170 * the system may not be busy. Pause to not flood. 171 */ 172 xc = xc_broadcast(XC_HIGHPRI, (xcfunc_t)nullop, NULL, NULL); 173 xc_wait(xc); 174 kpause("psrlz", false, 1, NULL); 175 176 mutex_spin_enter(&psz_lock); 177 } while (!kcpuset_iszero(psz->psz_target)); 178 179 psz_ev_excl.ev_count++; 180 mutex_spin_exit(&psz_lock); 181 182 psz->psz_owner = NULL; 183 } 184 185 int 186 pserialize_read_enter(void) 187 { 188 189 KASSERT(!cpu_intr_p()); 190 return splsoftserial(); 191 } 192 193 void 194 pserialize_read_exit(int s) 195 { 196 197 splx(s); 198 } 199 200 /* 201 * pserialize_switchpoint: 202 * 203 * Monitor system context switch activity. Called from machine 204 * independent code after mi_switch() returns. 205 */ 206 void 207 pserialize_switchpoint(void) 208 { 209 pserialize_t psz, next; 210 cpuid_t cid; 211 212 /* 213 * If no updates pending, bail out. No need to lock in order to 214 * test psz_work_todo; the only ill effect of missing an update 215 * would be to delay LWPs waiting in pserialize_perform(). That 216 * will not happen because updates are on the queue before an 217 * xcall is generated (serialization) to tickle every CPU. 218 */ 219 if (__predict_true(psz_work_todo == 0)) { 220 return; 221 } 222 mutex_spin_enter(&psz_lock); 223 cid = cpu_index(curcpu()); 224 225 /* 226 * At first, scan through the second queue and update each request, 227 * if passed all processors, then transfer to the third queue. 228 */ 229 for (psz = TAILQ_FIRST(&psz_queue1); psz != NULL; psz = next) { 230 next = TAILQ_NEXT(psz, psz_chain); 231 kcpuset_set(psz->psz_pass, cid); 232 if (!kcpuset_match(psz->psz_pass, psz->psz_target)) { 233 continue; 234 } 235 kcpuset_zero(psz->psz_pass); 236 TAILQ_REMOVE(&psz_queue1, psz, psz_chain); 237 TAILQ_INSERT_TAIL(&psz_queue2, psz, psz_chain); 238 } 239 /* 240 * Scan through the first queue and update each request, 241 * if passed all processors, then move to the second queue. 242 */ 243 for (psz = TAILQ_FIRST(&psz_queue0); psz != NULL; psz = next) { 244 next = TAILQ_NEXT(psz, psz_chain); 245 kcpuset_set(psz->psz_pass, cid); 246 if (!kcpuset_match(psz->psz_pass, psz->psz_target)) { 247 continue; 248 } 249 kcpuset_zero(psz->psz_pass); 250 TAILQ_REMOVE(&psz_queue0, psz, psz_chain); 251 TAILQ_INSERT_TAIL(&psz_queue1, psz, psz_chain); 252 } 253 /* 254 * Process the third queue: entries have been seen twice on every 255 * processor, remove from the queue and notify the updating thread. 256 */ 257 while ((psz = TAILQ_FIRST(&psz_queue2)) != NULL) { 258 TAILQ_REMOVE(&psz_queue2, psz, psz_chain); 259 kcpuset_zero(psz->psz_target); 260 psz_work_todo--; 261 } 262 mutex_spin_exit(&psz_lock); 263 } 264
Indexes created Mon Sep 29 21:09:56 GMT 2025