1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2018, Matthew Macy <mmacy@freebsd.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 * 27 */ 28 29 #include <sys/cdefs.h> 30 __FBSDID("$FreeBSD$"); 31 32 #include <sys/param.h> 33 #include <sys/types.h> 34 #include <sys/systm.h> 35 #include <sys/counter.h> 36 #include <sys/epoch.h> 37 #include <sys/gtaskqueue.h> 38 #include <sys/kernel.h> 39 #include <sys/limits.h> 40 #include <sys/lock.h> 41 #include <sys/malloc.h> 42 #include <sys/mutex.h> 43 #include <sys/pcpu.h> 44 #include <sys/proc.h> 45 #include <sys/sched.h> 46 #include <sys/smp.h> 47 #include <sys/sysctl.h> 48 #include <sys/turnstile.h> 49 #include <vm/vm.h> 50 #include <vm/vm_extern.h> 51 #include <vm/vm_kern.h> 52 #include <vm/uma.h> 53 54 #include <ck_epoch.h> 55 56 static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation"); 57 58 /* arbitrary --- needs benchmarking */ 59 #define MAX_ADAPTIVE_SPIN 100 60 #define MAX_EPOCHS 64 61 62 CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context)); 63 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information"); 64 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats"); 65 66 /* Stats. */ 67 static counter_u64_t block_count; 68 69 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW, 70 &block_count, "# of times a thread was in an epoch when epoch_wait was called"); 71 static counter_u64_t migrate_count; 72 73 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW, 74 &migrate_count, "# of times thread was migrated to another CPU in epoch_wait"); 75 static counter_u64_t turnstile_count; 76 77 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW, 78 &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait"); 79 static counter_u64_t switch_count; 80 81 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW, 82 &switch_count, "# of times a thread voluntarily context switched in epoch_wait"); 83 static counter_u64_t epoch_call_count; 84 85 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW, 86 &epoch_call_count, "# of times a callback was deferred"); 87 static counter_u64_t epoch_call_task_count; 88 89 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW, 90 &epoch_call_task_count, "# of times a callback task was run"); 91 92 TAILQ_HEAD (threadlist, thread); 93 94 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry, 95 ck_epoch_entry_container) 96 97 epoch_t allepochs[MAX_EPOCHS]; 98 99 DPCPU_DEFINE(struct grouptask, epoch_cb_task); 100 DPCPU_DEFINE(int, epoch_cb_count); 101 102 static __read_mostly int inited; 103 static __read_mostly int epoch_count; 104 __read_mostly epoch_t global_epoch; 105 __read_mostly epoch_t global_epoch_preempt; 106 107 static void epoch_call_task(void *context __unused); 108 static uma_zone_t pcpu_zone_record; 109 110 static void 111 epoch_init(void *arg __unused) 112 { 113 int cpu; 114 115 block_count = counter_u64_alloc(M_WAITOK); 116 migrate_count = counter_u64_alloc(M_WAITOK); 117 turnstile_count = counter_u64_alloc(M_WAITOK); 118 switch_count = counter_u64_alloc(M_WAITOK); 119 epoch_call_count = counter_u64_alloc(M_WAITOK); 120 epoch_call_task_count = counter_u64_alloc(M_WAITOK); 121 122 pcpu_zone_record = uma_zcreate("epoch_record pcpu", sizeof(struct epoch_record), 123 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_PCPU); 124 CPU_FOREACH(cpu) { 125 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0, epoch_call_task, NULL); 126 taskqgroup_attach_cpu(qgroup_softirq, DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, -1, "epoch call task"); 127 } 128 inited = 1; 129 global_epoch = epoch_alloc(0); 130 global_epoch_preempt = epoch_alloc(EPOCH_PREEMPT); 131 } 132 SYSINIT(epoch, SI_SUB_TASKQ + 1, SI_ORDER_FIRST, epoch_init, NULL); 133 134 #if !defined(EARLY_AP_STARTUP) 135 static void 136 epoch_init_smp(void *dummy __unused) 137 { 138 inited = 2; 139 } 140 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL); 141 #endif 142 143 static void 144 epoch_ctor(epoch_t epoch) 145 { 146 epoch_record_t er; 147 int cpu; 148 149 epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK); 150 CPU_FOREACH(cpu) { 151 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 152 bzero(er, sizeof(*er)); 153 ck_epoch_register(&epoch->e_epoch, &er->er_read_record, NULL); 154 ck_epoch_register(&epoch->e_epoch, &er->er_write_record, NULL); 155 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist); 156 er->er_cpuid = cpu; 157 } 158 } 159 160 epoch_t 161 epoch_alloc(int flags) 162 { 163 epoch_t epoch; 164 165 if (__predict_false(!inited)) 166 panic("%s called too early in boot", __func__); 167 epoch = malloc(sizeof(struct epoch), M_EPOCH, M_ZERO | M_WAITOK); 168 ck_epoch_init(&epoch->e_epoch); 169 epoch_ctor(epoch); 170 MPASS(epoch_count < MAX_EPOCHS - 2); 171 epoch->e_flags = flags; 172 epoch->e_idx = epoch_count; 173 allepochs[epoch_count++] = epoch; 174 return (epoch); 175 } 176 177 void 178 epoch_free(epoch_t epoch) 179 { 180 #ifdef INVARIANTS 181 struct epoch_record *er; 182 int cpu; 183 184 CPU_FOREACH(cpu) { 185 er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu); 186 MPASS(TAILQ_EMPTY(&er->er_tdlist)); 187 } 188 #endif 189 allepochs[epoch->e_idx] = NULL; 190 epoch_wait(global_epoch); 191 uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record); 192 free(epoch, M_EPOCH); 193 } 194 195 void 196 epoch_enter_preempt_KBI(epoch_t epoch, epoch_tracker_t et) 197 { 198 199 epoch_enter_preempt(epoch, et); 200 } 201 202 void 203 epoch_exit_preempt_KBI(epoch_t epoch, epoch_tracker_t et) 204 { 205 206 epoch_exit_preempt(epoch, et); 207 } 208 209 void 210 epoch_enter_KBI(epoch_t epoch) 211 { 212 213 epoch_enter(epoch); 214 } 215 216 void 217 epoch_exit_KBI(epoch_t epoch) 218 { 219 220 epoch_exit(epoch); 221 } 222 223 /* 224 * epoch_block_handler_preempt is a callback from the ck code when another thread is 225 * currently in an epoch section. 226 */ 227 static void 228 epoch_block_handler_preempt(struct ck_epoch *global __unused, ck_epoch_record_t *cr, 229 void *arg __unused) 230 { 231 epoch_record_t record; 232 struct thread *td, *owner, *curwaittd; 233 struct epoch_thread *tdwait; 234 struct turnstile *ts; 235 struct lock_object *lock; 236 int spincount, gen; 237 int locksheld __unused; 238 239 record = __containerof(cr, struct epoch_record, er_read_record); 240 td = curthread; 241 locksheld = td->td_locks; 242 spincount = 0; 243 counter_u64_add(block_count, 1); 244 /* 245 * We lost a race and there's no longer any threads 246 * on the CPU in an epoch section. 247 */ 248 if (TAILQ_EMPTY(&record->er_tdlist)) 249 return; 250 251 if (record->er_cpuid != curcpu) { 252 /* 253 * If the head of the list is running, we can wait for it 254 * to remove itself from the list and thus save us the 255 * overhead of a migration 256 */ 257 gen = record->er_gen; 258 thread_unlock(td); 259 /* 260 * We can't actually check if the waiting thread is running 261 * so we simply poll for it to exit before giving up and 262 * migrating. 263 */ 264 do { 265 cpu_spinwait(); 266 } while (!TAILQ_EMPTY(&record->er_tdlist) && 267 gen == record->er_gen && 268 spincount++ < MAX_ADAPTIVE_SPIN); 269 thread_lock(td); 270 /* 271 * If the generation has changed we can poll again 272 * otherwise we need to migrate. 273 */ 274 if (gen != record->er_gen) 275 return; 276 /* 277 * Being on the same CPU as that of the record on which 278 * we need to wait allows us access to the thread 279 * list associated with that CPU. We can then examine the 280 * oldest thread in the queue and wait on its turnstile 281 * until it resumes and so on until a grace period 282 * elapses. 283 * 284 */ 285 counter_u64_add(migrate_count, 1); 286 sched_bind(td, record->er_cpuid); 287 /* 288 * At this point we need to return to the ck code 289 * to scan to see if a grace period has elapsed. 290 * We can't move on to check the thread list, because 291 * in the meantime new threads may have arrived that 292 * in fact belong to a different epoch. 293 */ 294 return; 295 } 296 /* 297 * Try to find a thread in an epoch section on this CPU 298 * waiting on a turnstile. Otherwise find the lowest 299 * priority thread (highest prio value) and drop our priority 300 * to match to allow it to run. 301 */ 302 TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) { 303 /* 304 * Propagate our priority to any other waiters to prevent us 305 * from starving them. They will have their original priority 306 * restore on exit from epoch_wait(). 307 */ 308 curwaittd = tdwait->et_td; 309 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) { 310 critical_enter(); 311 thread_unlock(td); 312 thread_lock(curwaittd); 313 sched_prio(curwaittd, td->td_priority); 314 thread_unlock(curwaittd); 315 thread_lock(td); 316 critical_exit(); 317 } 318 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) && 319 ((ts = curwaittd->td_blocked) != NULL)) { 320 /* 321 * We unlock td to allow turnstile_wait to reacquire the 322 * the thread lock. Before unlocking it we enter a critical 323 * section to prevent preemption after we reenable interrupts 324 * by dropping the thread lock in order to prevent curwaittd 325 * from getting to run. 326 */ 327 critical_enter(); 328 thread_unlock(td); 329 owner = turnstile_lock(ts, &lock); 330 /* 331 * The owner pointer indicates that the lock succeeded. Only 332 * in case we hold the lock and the turnstile we locked is still 333 * the one that curwaittd is blocked on can we continue. Otherwise 334 * The turnstile pointer has been changed out from underneath 335 * us, as in the case where the lock holder has signalled curwaittd, 336 * and we need to continue. 337 */ 338 if (owner != NULL && ts == curwaittd->td_blocked) { 339 MPASS(TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd)); 340 critical_exit(); 341 turnstile_wait(ts, owner, curwaittd->td_tsqueue); 342 counter_u64_add(turnstile_count, 1); 343 thread_lock(td); 344 return; 345 } else if (owner != NULL) 346 turnstile_unlock(ts, lock); 347 thread_lock(td); 348 critical_exit(); 349 KASSERT(td->td_locks == locksheld, 350 ("%d extra locks held", td->td_locks - locksheld)); 351 } 352 } 353 /* 354 * We didn't find any threads actually blocked on a lock 355 * so we have nothing to do except context switch away. 356 */ 357 counter_u64_add(switch_count, 1); 358 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 359 360 /* 361 * Release the thread lock while yielding to 362 * allow other threads to acquire the lock 363 * pointed to by TDQ_LOCKPTR(td). Else a 364 * deadlock like situation might happen. (HPS) 365 */ 366 thread_unlock(td); 367 thread_lock(td); 368 } 369 370 void 371 epoch_wait_preempt(epoch_t epoch) 372 { 373 struct thread *td; 374 int was_bound; 375 int old_cpu; 376 int old_pinned; 377 u_char old_prio; 378 int locks __unused; 379 380 MPASS(cold || epoch != NULL); 381 INIT_CHECK(epoch); 382 td = curthread; 383 #ifdef INVARIANTS 384 locks = curthread->td_locks; 385 MPASS(epoch->e_flags & EPOCH_PREEMPT); 386 if ((epoch->e_flags & EPOCH_LOCKED) == 0) 387 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 388 "epoch_wait() can be long running"); 389 KASSERT(!in_epoch(epoch), 390 ("epoch_wait_preempt() called in the middle " 391 "of an epoch section of the same epoch")); 392 #endif 393 thread_lock(td); 394 DROP_GIANT(); 395 396 old_cpu = PCPU_GET(cpuid); 397 old_pinned = td->td_pinned; 398 old_prio = td->td_priority; 399 was_bound = sched_is_bound(td); 400 sched_unbind(td); 401 td->td_pinned = 0; 402 sched_bind(td, old_cpu); 403 404 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt, NULL); 405 406 /* restore CPU binding, if any */ 407 if (was_bound != 0) { 408 sched_bind(td, old_cpu); 409 } else { 410 /* get thread back to initial CPU, if any */ 411 if (old_pinned != 0) 412 sched_bind(td, old_cpu); 413 sched_unbind(td); 414 } 415 /* restore pinned after bind */ 416 td->td_pinned = old_pinned; 417 418 /* restore thread priority */ 419 sched_prio(td, old_prio); 420 thread_unlock(td); 421 PICKUP_GIANT(); 422 KASSERT(td->td_locks == locks, 423 ("%d residual locks held", td->td_locks - locks)); 424 } 425 426 static void 427 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused, 428 void *arg __unused) 429 { 430 cpu_spinwait(); 431 } 432 433 void 434 epoch_wait(epoch_t epoch) 435 { 436 437 MPASS(cold || epoch != NULL); 438 INIT_CHECK(epoch); 439 MPASS(epoch->e_flags == 0); 440 critical_enter(); 441 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL); 442 critical_exit(); 443 } 444 445 void 446 epoch_call(epoch_t epoch, epoch_context_t ctx, void (*callback) (epoch_context_t)) 447 { 448 epoch_record_t er; 449 ck_epoch_entry_t *cb; 450 451 cb = (void *)ctx; 452 453 MPASS(callback); 454 /* too early in boot to have epoch set up */ 455 if (__predict_false(epoch == NULL)) 456 goto boottime; 457 #if !defined(EARLY_AP_STARTUP) 458 if (__predict_false(inited < 2)) 459 goto boottime; 460 #endif 461 462 critical_enter(); 463 *DPCPU_PTR(epoch_cb_count) += 1; 464 er = epoch_currecord(epoch); 465 ck_epoch_call(&er->er_write_record, cb, (ck_epoch_cb_t *)callback); 466 critical_exit(); 467 return; 468 boottime: 469 callback(ctx); 470 } 471 472 static void 473 epoch_call_task(void *arg __unused) 474 { 475 ck_stack_entry_t *cursor, *head, *next; 476 ck_epoch_record_t *record; 477 epoch_record_t er; 478 epoch_t epoch; 479 ck_stack_t cb_stack; 480 int i, npending, total; 481 482 ck_stack_init(&cb_stack); 483 critical_enter(); 484 epoch_enter(global_epoch); 485 for (total = i = 0; i < epoch_count; i++) { 486 if (__predict_false((epoch = allepochs[i]) == NULL)) 487 continue; 488 er = epoch_currecord(epoch); 489 record = &er->er_write_record; 490 if ((npending = record->n_pending) == 0) 491 continue; 492 ck_epoch_poll_deferred(record, &cb_stack); 493 total += npending - record->n_pending; 494 } 495 epoch_exit(global_epoch); 496 *DPCPU_PTR(epoch_cb_count) -= total; 497 critical_exit(); 498 499 counter_u64_add(epoch_call_count, total); 500 counter_u64_add(epoch_call_task_count, 1); 501 502 head = ck_stack_batch_pop_npsc(&cb_stack); 503 for (cursor = head; cursor != NULL; cursor = next) { 504 struct ck_epoch_entry *entry = 505 ck_epoch_entry_container(cursor); 506 507 next = CK_STACK_NEXT(cursor); 508 entry->function(entry); 509 } 510 } 511 512 int 513 in_epoch_verbose(epoch_t epoch, int dump_onfail) 514 { 515 struct epoch_thread *tdwait; 516 struct thread *td; 517 epoch_record_t er; 518 519 td = curthread; 520 if (td->td_epochnest == 0) 521 return (0); 522 if (__predict_false((epoch) == NULL)) 523 return (0); 524 critical_enter(); 525 er = epoch_currecord(epoch); 526 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 527 if (tdwait->et_td == td) { 528 critical_exit(); 529 return (1); 530 } 531 #ifdef INVARIANTS 532 if (dump_onfail) { 533 MPASS(td->td_pinned); 534 printf("cpu: %d id: %d\n", curcpu, td->td_tid); 535 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link) 536 printf("td_tid: %d ", tdwait->et_td->td_tid); 537 printf("\n"); 538 } 539 #endif 540 critical_exit(); 541 return (0); 542 } 543 544 int 545 in_epoch(epoch_t epoch) 546 { 547 return (in_epoch_verbose(epoch, 0)); 548 } 549 550 void 551 epoch_adjust_prio(struct thread *td, u_char prio) 552 { 553 thread_lock(td); 554 sched_prio(td, prio); 555 thread_unlock(td); 556 } 557