subr_percpu.c revision 1.18
1 /* $NetBSD: subr_percpu.c,v 1.18 2017/05/31 23:54:17 chs Exp $ */ 2 3 /*- 4 * Copyright (c)2007,2008 YAMAMOTO Takashi, 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 AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 /* 30 * per-cpu storage. 31 */ 32 33 #include <sys/cdefs.h> 34 __KERNEL_RCSID(0, "$NetBSD: subr_percpu.c,v 1.18 2017/05/31 23:54:17 chs Exp $"); 35 36 #include <sys/param.h> 37 #include <sys/cpu.h> 38 #include <sys/kmem.h> 39 #include <sys/kernel.h> 40 #include <sys/mutex.h> 41 #include <sys/percpu.h> 42 #include <sys/rwlock.h> 43 #include <sys/vmem.h> 44 #include <sys/xcall.h> 45 46 #define PERCPU_QUANTUM_SIZE (ALIGNBYTES + 1) 47 #define PERCPU_QCACHE_MAX 0 48 #define PERCPU_IMPORT_SIZE 2048 49 50 #if defined(DIAGNOSTIC) 51 #define MAGIC 0x50435055 /* "PCPU" */ 52 #define percpu_encrypt(pc) ((pc) ^ MAGIC) 53 #define percpu_decrypt(pc) ((pc) ^ MAGIC) 54 #else /* defined(DIAGNOSTIC) */ 55 #define percpu_encrypt(pc) (pc) 56 #define percpu_decrypt(pc) (pc) 57 #endif /* defined(DIAGNOSTIC) */ 58 59 static krwlock_t percpu_swap_lock __cacheline_aligned; 60 static kmutex_t percpu_allocation_lock __cacheline_aligned; 61 static vmem_t * percpu_offset_arena __cacheline_aligned; 62 static unsigned int percpu_nextoff __cacheline_aligned; 63 64 static percpu_cpu_t * 65 cpu_percpu(struct cpu_info *ci) 66 { 67 68 return &ci->ci_data.cpu_percpu; 69 } 70 71 static unsigned int 72 percpu_offset(percpu_t *pc) 73 { 74 const unsigned int off = percpu_decrypt((uintptr_t)pc); 75 76 KASSERT(off < percpu_nextoff); 77 return off; 78 } 79 80 /* 81 * percpu_cpu_swap: crosscall handler for percpu_cpu_enlarge 82 */ 83 84 static void 85 percpu_cpu_swap(void *p1, void *p2) 86 { 87 struct cpu_info * const ci = p1; 88 percpu_cpu_t * const newpcc = p2; 89 percpu_cpu_t * const pcc = cpu_percpu(ci); 90 91 KASSERT(ci == curcpu() || !mp_online); 92 93 /* 94 * swap *pcc and *newpcc unless anyone has beaten us. 95 */ 96 rw_enter(&percpu_swap_lock, RW_WRITER); 97 if (newpcc->pcc_size > pcc->pcc_size) { 98 percpu_cpu_t tmp; 99 int s; 100 101 tmp = *pcc; 102 103 /* 104 * block interrupts so that we don't lose their modifications. 105 */ 106 107 s = splhigh(); 108 109 /* 110 * copy data to new storage. 111 */ 112 113 memcpy(newpcc->pcc_data, pcc->pcc_data, pcc->pcc_size); 114 115 /* 116 * this assignment needs to be atomic for percpu_getptr_remote. 117 */ 118 119 pcc->pcc_data = newpcc->pcc_data; 120 121 splx(s); 122 123 pcc->pcc_size = newpcc->pcc_size; 124 *newpcc = tmp; 125 } 126 rw_exit(&percpu_swap_lock); 127 } 128 129 /* 130 * percpu_cpu_enlarge: ensure that percpu_cpu_t of each cpus have enough space 131 */ 132 133 static void 134 percpu_cpu_enlarge(size_t size) 135 { 136 CPU_INFO_ITERATOR cii; 137 struct cpu_info *ci; 138 139 for (CPU_INFO_FOREACH(cii, ci)) { 140 percpu_cpu_t pcc; 141 142 pcc.pcc_data = kmem_alloc(size, KM_SLEEP); /* XXX cacheline */ 143 pcc.pcc_size = size; 144 if (!mp_online) { 145 percpu_cpu_swap(ci, &pcc); 146 } else { 147 uint64_t where; 148 149 where = xc_unicast(0, percpu_cpu_swap, ci, &pcc, ci); 150 xc_wait(where); 151 } 152 KASSERT(pcc.pcc_size < size); 153 if (pcc.pcc_data != NULL) { 154 kmem_free(pcc.pcc_data, pcc.pcc_size); 155 } 156 } 157 } 158 159 /* 160 * percpu_backend_alloc: vmem import callback for percpu_offset_arena 161 */ 162 163 static int 164 percpu_backend_alloc(vmem_t *dummy, vmem_size_t size, vmem_size_t *resultsize, 165 vm_flag_t vmflags, vmem_addr_t *addrp) 166 { 167 unsigned int offset; 168 unsigned int nextoff; 169 170 ASSERT_SLEEPABLE(); 171 KASSERT(dummy == NULL); 172 173 if ((vmflags & VM_NOSLEEP) != 0) 174 return ENOMEM; 175 176 size = roundup(size, PERCPU_IMPORT_SIZE); 177 mutex_enter(&percpu_allocation_lock); 178 offset = percpu_nextoff; 179 percpu_nextoff = nextoff = percpu_nextoff + size; 180 mutex_exit(&percpu_allocation_lock); 181 182 percpu_cpu_enlarge(nextoff); 183 184 *resultsize = size; 185 *addrp = (vmem_addr_t)offset; 186 return 0; 187 } 188 189 static void 190 percpu_zero_cb(void *vp, void *vp2, struct cpu_info *ci) 191 { 192 size_t sz = (uintptr_t)vp2; 193 194 memset(vp, 0, sz); 195 } 196 197 /* 198 * percpu_zero: initialize percpu storage with zero. 199 */ 200 201 static void 202 percpu_zero(percpu_t *pc, size_t sz) 203 { 204 205 percpu_foreach(pc, percpu_zero_cb, (void *)(uintptr_t)sz); 206 } 207 208 /* 209 * percpu_init: subsystem initialization 210 */ 211 212 void 213 percpu_init(void) 214 { 215 216 ASSERT_SLEEPABLE(); 217 rw_init(&percpu_swap_lock); 218 mutex_init(&percpu_allocation_lock, MUTEX_DEFAULT, IPL_NONE); 219 percpu_nextoff = PERCPU_QUANTUM_SIZE; 220 221 percpu_offset_arena = vmem_xcreate("percpu", 0, 0, PERCPU_QUANTUM_SIZE, 222 percpu_backend_alloc, NULL, NULL, PERCPU_QCACHE_MAX, VM_SLEEP, 223 IPL_NONE); 224 } 225 226 /* 227 * percpu_init_cpu: cpu initialization 228 * 229 * => should be called before the cpu appears on the list for CPU_INFO_FOREACH. 230 */ 231 232 void 233 percpu_init_cpu(struct cpu_info *ci) 234 { 235 percpu_cpu_t * const pcc = cpu_percpu(ci); 236 size_t size = percpu_nextoff; /* XXX racy */ 237 238 ASSERT_SLEEPABLE(); 239 pcc->pcc_size = size; 240 if (size) { 241 pcc->pcc_data = kmem_zalloc(pcc->pcc_size, KM_SLEEP); 242 } 243 } 244 245 /* 246 * percpu_alloc: allocate percpu storage 247 * 248 * => called in thread context. 249 * => considered as an expensive and rare operation. 250 * => allocated storage is initialized with zeros. 251 */ 252 253 percpu_t * 254 percpu_alloc(size_t size) 255 { 256 vmem_addr_t offset; 257 percpu_t *pc; 258 259 ASSERT_SLEEPABLE(); 260 (void)vmem_alloc(percpu_offset_arena, size, VM_SLEEP | VM_BESTFIT, 261 &offset); 262 pc = (percpu_t *)percpu_encrypt((uintptr_t)offset); 263 percpu_zero(pc, size); 264 return pc; 265 } 266 267 /* 268 * percpu_free: free percpu storage 269 * 270 * => called in thread context. 271 * => considered as an expensive and rare operation. 272 */ 273 274 void 275 percpu_free(percpu_t *pc, size_t size) 276 { 277 278 ASSERT_SLEEPABLE(); 279 vmem_free(percpu_offset_arena, (vmem_addr_t)percpu_offset(pc), size); 280 } 281 282 /* 283 * percpu_getref: 284 * 285 * => safe to be used in either thread or interrupt context 286 * => disables preemption; must be bracketed with a percpu_putref() 287 */ 288 289 void * 290 percpu_getref(percpu_t *pc) 291 { 292 293 kpreempt_disable(); 294 return percpu_getptr_remote(pc, curcpu()); 295 } 296 297 /* 298 * percpu_putref: 299 * 300 * => drops the preemption-disabled count after caller is done with per-cpu 301 * data 302 */ 303 304 void 305 percpu_putref(percpu_t *pc) 306 { 307 308 kpreempt_enable(); 309 } 310 311 /* 312 * percpu_traverse_enter, percpu_traverse_exit, percpu_getptr_remote: 313 * helpers to access remote cpu's percpu data. 314 * 315 * => called in thread context. 316 * => percpu_traverse_enter can block low-priority xcalls. 317 * => typical usage would be: 318 * 319 * sum = 0; 320 * percpu_traverse_enter(); 321 * for (CPU_INFO_FOREACH(cii, ci)) { 322 * unsigned int *p = percpu_getptr_remote(pc, ci); 323 * sum += *p; 324 * } 325 * percpu_traverse_exit(); 326 */ 327 328 void 329 percpu_traverse_enter(void) 330 { 331 332 ASSERT_SLEEPABLE(); 333 rw_enter(&percpu_swap_lock, RW_READER); 334 } 335 336 void 337 percpu_traverse_exit(void) 338 { 339 340 rw_exit(&percpu_swap_lock); 341 } 342 343 void * 344 percpu_getptr_remote(percpu_t *pc, struct cpu_info *ci) 345 { 346 347 return &((char *)cpu_percpu(ci)->pcc_data)[percpu_offset(pc)]; 348 } 349 350 /* 351 * percpu_foreach: call the specified callback function for each cpus. 352 * 353 * => called in thread context. 354 * => caller should not rely on the cpu iteration order. 355 * => the callback function should be minimum because it is executed with 356 * holding a global lock, which can block low-priority xcalls. 357 * eg. it's illegal for a callback function to sleep for memory allocation. 358 */ 359 void 360 percpu_foreach(percpu_t *pc, percpu_callback_t cb, void *arg) 361 { 362 CPU_INFO_ITERATOR cii; 363 struct cpu_info *ci; 364 365 percpu_traverse_enter(); 366 for (CPU_INFO_FOREACH(cii, ci)) { 367 (*cb)(percpu_getptr_remote(pc, ci), arg, ci); 368 } 369 percpu_traverse_exit(); 370 } 371
Indexes created Sun Sep 21 20:09:37 GMT 2025