| 1 | /* $NetBSD: subr_pserialize.c,v 1.8 2015/06/12 19:18:30 dholland 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 1.8 2015/06/12 19:18:30 dholland 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_switchto(). 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 | |