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/proc.h> 44 #include <sys/sched.h> 45 #include <sys/smp.h> 46 #include <sys/sysctl.h> 47 #include <sys/turnstile.h> 48 #include <vm/vm.h> 49 #include <vm/vm_extern.h> 50 #include <vm/vm_kern.h> 51 52 #include <ck_epoch.h> 53 54 static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation"); 55 56 /* arbitrary --- needs benchmarking */ 57 #define MAX_ADAPTIVE_SPIN 5000 58 59 #define EPOCH_EXITING 0x1 60 #ifdef __amd64__ 61 #define EPOCH_ALIGN CACHE_LINE_SIZE*2 62 #else 63 #define EPOCH_ALIGN CACHE_LINE_SIZE 64 #endif 65 66 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information"); 67 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats"); 68 69 static int poll_intvl; 70 SYSCTL_INT(_kern_epoch, OID_AUTO, poll_intvl, CTLFLAG_RWTUN, 71 &poll_intvl, 0, "# of ticks to wait between garbage collecting deferred frees"); 72 /* Stats. */ 73 static counter_u64_t block_count; 74 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW, 75 &block_count, "# of times a thread was in an epoch when epoch_wait was called"); 76 static counter_u64_t migrate_count; 77 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW, 78 &migrate_count, "# of times thread was migrated to another CPU in epoch_wait"); 79 static counter_u64_t turnstile_count; 80 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW, 81 &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait"); 82 static counter_u64_t switch_count; 83 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW, 84 &switch_count, "# of times a thread voluntarily context switched in epoch_wait"); 85 86 typedef struct epoch_cb { 87 void (*ec_callback)(epoch_context_t); 88 STAILQ_ENTRY(epoch_cb) ec_link; 89 } *epoch_cb_t; 90 91 TAILQ_HEAD(threadlist, thread); 92 93 typedef struct epoch_record { 94 ck_epoch_record_t er_record; 95 volatile struct threadlist er_tdlist; 96 volatile uint32_t er_gen; 97 uint32_t er_cpuid; 98 } *epoch_record_t; 99 100 struct epoch_pcpu_state { 101 struct epoch_record eps_record; 102 STAILQ_HEAD(, epoch_cb) eps_cblist; 103 } __aligned(EPOCH_ALIGN); 104 105 struct epoch { 106 struct ck_epoch e_epoch __aligned(EPOCH_ALIGN); 107 struct grouptask e_gtask; 108 struct callout e_timer; 109 struct mtx e_lock; 110 int e_flags; 111 /* make sure that immutable data doesn't overlap with the gtask, callout, and mutex*/ 112 struct epoch_pcpu_state *e_pcpu_dom[MAXMEMDOM] __aligned(EPOCH_ALIGN); 113 counter_u64_t e_frees; 114 uint64_t e_free_last; 115 struct epoch_pcpu_state *e_pcpu[0]; 116 }; 117 118 static __read_mostly int domcount[MAXMEMDOM]; 119 static __read_mostly int domoffsets[MAXMEMDOM]; 120 static __read_mostly int inited; 121 __read_mostly epoch_t global_epoch; 122 123 static void epoch_call_task(void *context); 124 125 #if defined(__powerpc64__) || defined(__powerpc__) || !defined(NUMA) 126 static bool usedomains = false; 127 #else 128 static bool usedomains = true; 129 #endif 130 static void 131 epoch_init(void *arg __unused) 132 { 133 int domain, count; 134 135 if (poll_intvl == 0) 136 poll_intvl = hz; 137 138 block_count = counter_u64_alloc(M_WAITOK); 139 migrate_count = counter_u64_alloc(M_WAITOK); 140 turnstile_count = counter_u64_alloc(M_WAITOK); 141 switch_count = counter_u64_alloc(M_WAITOK); 142 if (usedomains == false) 143 goto done; 144 count = domain = 0; 145 domoffsets[0] = 0; 146 for (domain = 0; domain < vm_ndomains; domain++) { 147 domcount[domain] = CPU_COUNT(&cpuset_domain[domain]); 148 if (bootverbose) 149 printf("domcount[%d] %d\n", domain, domcount[domain]); 150 } 151 for (domain = 1; domain < vm_ndomains; domain++) 152 domoffsets[domain] = domoffsets[domain-1] + domcount[domain-1]; 153 154 for (domain = 0; domain < vm_ndomains; domain++) { 155 if (domcount[domain] == 0) { 156 usedomains = false; 157 break; 158 } 159 } 160 done: 161 inited = 1; 162 global_epoch = epoch_alloc(); 163 } 164 SYSINIT(epoch, SI_SUB_TASKQ + 1, SI_ORDER_FIRST, epoch_init, NULL); 165 166 static void 167 epoch_init_numa(epoch_t epoch) 168 { 169 int domain, cpu_offset; 170 struct epoch_pcpu_state *eps; 171 epoch_record_t er; 172 173 for (domain = 0; domain < vm_ndomains; domain++) { 174 eps = malloc_domain(sizeof(*eps)*domcount[domain], M_EPOCH, 175 domain, M_ZERO|M_WAITOK); 176 epoch->e_pcpu_dom[domain] = eps; 177 cpu_offset = domoffsets[domain]; 178 for (int i = 0; i < domcount[domain]; i++, eps++) { 179 epoch->e_pcpu[cpu_offset + i] = eps; 180 er = &eps->eps_record; 181 STAILQ_INIT(&eps->eps_cblist); 182 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL); 183 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist); 184 er->er_cpuid = cpu_offset + i; 185 } 186 } 187 } 188 189 static void 190 epoch_init_legacy(epoch_t epoch) 191 { 192 struct epoch_pcpu_state *eps; 193 epoch_record_t er; 194 195 eps = malloc(sizeof(*eps)*mp_ncpus, M_EPOCH, M_ZERO|M_WAITOK); 196 epoch->e_pcpu_dom[0] = eps; 197 for (int i = 0; i < mp_ncpus; i++, eps++) { 198 epoch->e_pcpu[i] = eps; 199 er = &eps->eps_record; 200 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL); 201 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist); 202 STAILQ_INIT(&eps->eps_cblist); 203 er->er_cpuid = i; 204 } 205 } 206 207 static void 208 epoch_callout(void *arg) 209 { 210 epoch_t epoch; 211 uint64_t frees; 212 213 epoch = arg; 214 frees = counter_u64_fetch(epoch->e_frees); 215 /* pick some better value */ 216 if (frees - epoch->e_free_last > 10) { 217 GROUPTASK_ENQUEUE(&epoch->e_gtask); 218 epoch->e_free_last = frees; 219 } 220 if ((epoch->e_flags & EPOCH_EXITING) == 0) 221 callout_reset(&epoch->e_timer, poll_intvl, epoch_callout, epoch); 222 } 223 224 epoch_t 225 epoch_alloc(void) 226 { 227 epoch_t epoch; 228 229 if (__predict_false(!inited)) 230 panic("%s called too early in boot", __func__); 231 epoch = malloc(sizeof(struct epoch) + mp_ncpus*sizeof(void*), 232 M_EPOCH, M_ZERO|M_WAITOK); 233 ck_epoch_init(&epoch->e_epoch); 234 epoch->e_frees = counter_u64_alloc(M_WAITOK); 235 mtx_init(&epoch->e_lock, "epoch callout", NULL, MTX_DEF); 236 callout_init_mtx(&epoch->e_timer, &epoch->e_lock, 0); 237 taskqgroup_config_gtask_init(epoch, &epoch->e_gtask, epoch_call_task, "epoch call task"); 238 if (usedomains) 239 epoch_init_numa(epoch); 240 else 241 epoch_init_legacy(epoch); 242 callout_reset(&epoch->e_timer, poll_intvl, epoch_callout, epoch); 243 return (epoch); 244 } 245 246 void 247 epoch_free(epoch_t epoch) 248 { 249 int domain; 250 #ifdef INVARIANTS 251 struct epoch_pcpu_state *eps; 252 int cpu; 253 254 CPU_FOREACH(cpu) { 255 eps = epoch->e_pcpu[cpu]; 256 MPASS(TAILQ_EMPTY(&eps->eps_record.er_tdlist)); 257 } 258 #endif 259 mtx_lock(&epoch->e_lock); 260 epoch->e_flags |= EPOCH_EXITING; 261 mtx_unlock(&epoch->e_lock); 262 /* 263 * Execute any lingering callbacks 264 */ 265 GROUPTASK_ENQUEUE(&epoch->e_gtask); 266 gtaskqueue_drain(epoch->e_gtask.gt_taskqueue, &epoch->e_gtask.gt_task); 267 callout_drain(&epoch->e_timer); 268 mtx_destroy(&epoch->e_lock); 269 counter_u64_free(epoch->e_frees); 270 taskqgroup_config_gtask_deinit(&epoch->e_gtask); 271 if (usedomains) 272 for (domain = 0; domain < vm_ndomains; domain++) 273 free_domain(epoch->e_pcpu_dom[domain], M_EPOCH); 274 else 275 free(epoch->e_pcpu_dom[0], M_EPOCH); 276 free(epoch, M_EPOCH); 277 } 278 279 #define INIT_CHECK(epoch) \ 280 do { \ 281 if (__predict_false((epoch) == NULL)) \ 282 return; \ 283 } while (0) 284 285 void 286 epoch_enter(epoch_t epoch) 287 { 288 struct epoch_pcpu_state *eps; 289 struct thread *td; 290 291 INIT_CHECK(epoch); 292 293 td = curthread; 294 critical_enter(); 295 eps = epoch->e_pcpu[curcpu]; 296 td->td_epochnest++; 297 MPASS(td->td_epochnest < UCHAR_MAX - 2); 298 if (td->td_epochnest == 1) 299 TAILQ_INSERT_TAIL(&eps->eps_record.er_tdlist, td, td_epochq); 300 #ifdef INVARIANTS 301 if (td->td_epochnest > 1) { 302 struct thread *curtd; 303 int found = 0; 304 305 TAILQ_FOREACH(curtd, &eps->eps_record.er_tdlist, td_epochq) 306 if (curtd == td) 307 found = 1; 308 KASSERT(found, ("recursing on a second epoch")); 309 } 310 #endif 311 sched_pin(); 312 ck_epoch_begin(&eps->eps_record.er_record, NULL); 313 critical_exit(); 314 } 315 316 void 317 epoch_exit(epoch_t epoch) 318 { 319 struct epoch_pcpu_state *eps; 320 struct thread *td; 321 322 td = curthread; 323 INIT_CHECK(epoch); 324 MPASS(td->td_epochnest); 325 critical_enter(); 326 eps = epoch->e_pcpu[curcpu]; 327 sched_unpin(); 328 ck_epoch_end(&eps->eps_record.er_record, NULL); 329 td->td_epochnest--; 330 if (td->td_epochnest == 0) 331 TAILQ_REMOVE(&eps->eps_record.er_tdlist, td, td_epochq); 332 eps->eps_record.er_gen++; 333 critical_exit(); 334 } 335 336 /* 337 * epoch_block_handler is a callback from the ck code when another thread is 338 * currently in an epoch section. 339 */ 340 static void 341 epoch_block_handler(struct ck_epoch *global __unused, ck_epoch_record_t *cr, 342 void *arg __unused) 343 { 344 epoch_record_t record; 345 struct epoch_pcpu_state *eps; 346 struct thread *td, *tdwait, *owner; 347 struct turnstile *ts; 348 struct lock_object *lock; 349 int spincount, gen; 350 351 eps = arg; 352 record = __containerof(cr, struct epoch_record, er_record); 353 td = curthread; 354 spincount = 0; 355 counter_u64_add(block_count, 1); 356 if (record->er_cpuid != curcpu) { 357 /* 358 * If the head of the list is running, we can wait for it 359 * to remove itself from the list and thus save us the 360 * overhead of a migration 361 */ 362 if ((tdwait = TAILQ_FIRST(&record->er_tdlist)) != NULL && 363 TD_IS_RUNNING(tdwait)) { 364 gen = record->er_gen; 365 thread_unlock(td); 366 do { 367 cpu_spinwait(); 368 } while (tdwait == TAILQ_FIRST(&record->er_tdlist) && 369 gen == record->er_gen && TD_IS_RUNNING(tdwait) && 370 spincount++ < MAX_ADAPTIVE_SPIN); 371 thread_lock(td); 372 return; 373 } 374 375 /* 376 * Being on the same CPU as that of the record on which 377 * we need to wait allows us access to the thread 378 * list associated with that CPU. We can then examine the 379 * oldest thread in the queue and wait on its turnstile 380 * until it resumes and so on until a grace period 381 * elapses. 382 * 383 */ 384 counter_u64_add(migrate_count, 1); 385 sched_bind(td, record->er_cpuid); 386 /* 387 * At this point we need to return to the ck code 388 * to scan to see if a grace period has elapsed. 389 * We can't move on to check the thread list, because 390 * in the meantime new threads may have arrived that 391 * in fact belong to a different epoch. 392 */ 393 return; 394 } 395 /* 396 * Try to find a thread in an epoch section on this CPU 397 * waiting on a turnstile. Otherwise find the lowest 398 * priority thread (highest prio value) and drop our priority 399 * to match to allow it to run. 400 */ 401 TAILQ_FOREACH(tdwait, &record->er_tdlist, td_epochq) { 402 /* 403 * Propagate our priority to any other waiters to prevent us 404 * from starving them. They will have their original priority 405 * restore on exit from epoch_wait(). 406 */ 407 if (!TD_IS_INHIBITED(tdwait) && tdwait->td_priority > td->td_priority) { 408 thread_lock(tdwait); 409 sched_prio(tdwait, td->td_priority); 410 thread_unlock(tdwait); 411 } 412 if (TD_IS_INHIBITED(tdwait) && TD_ON_LOCK(tdwait) && 413 ((ts = tdwait->td_blocked) != NULL)) { 414 /* 415 * We unlock td to allow turnstile_wait to reacquire the 416 * the thread lock. Before unlocking it we enter a critical 417 * section to prevent preemption after we reenable interrupts 418 * by dropping the thread lock in order to prevent tdwait 419 * from getting to run. 420 */ 421 critical_enter(); 422 thread_unlock(td); 423 owner = turnstile_lock(ts, &lock); 424 /* 425 * The owner pointer indicates that the lock succeeded. Only 426 * in case we hold the lock and the turnstile we locked is still 427 * the one that tdwait is blocked on can we continue. Otherwise 428 * The turnstile pointer has been changed out from underneath 429 * us, as in the case where the lock holder has signalled tdwait, 430 * and we need to continue. 431 */ 432 if (owner != NULL && ts == tdwait->td_blocked) { 433 MPASS(TD_IS_INHIBITED(tdwait) && TD_ON_LOCK(tdwait)); 434 critical_exit(); 435 turnstile_wait(ts, owner, tdwait->td_tsqueue); 436 counter_u64_add(turnstile_count, 1); 437 thread_lock(td); 438 return; 439 } else if (owner != NULL) 440 turnstile_unlock(ts, lock); 441 thread_lock(td); 442 critical_exit(); 443 KASSERT(td->td_locks == 0, 444 ("%d locks held", td->td_locks)); 445 } 446 } 447 /* 448 * We didn't find any threads actually blocked on a lock 449 * so we have nothing to do except context switch away. 450 */ 451 counter_u64_add(switch_count, 1); 452 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 453 454 /* 455 * Release the thread lock while yielding to 456 * allow other threads to acquire the lock 457 * pointed to by TDQ_LOCKPTR(td). Else a 458 * deadlock like situation might happen. (HPS) 459 */ 460 thread_unlock(td); 461 thread_lock(td); 462 } 463 464 void 465 epoch_wait(epoch_t epoch) 466 { 467 struct thread *td; 468 int was_bound; 469 int old_cpu; 470 int old_pinned; 471 u_char old_prio; 472 #ifdef INVARIANTS 473 int locks; 474 475 locks = curthread->td_locks; 476 #endif 477 INIT_CHECK(epoch); 478 479 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 480 "epoch_wait() can sleep"); 481 482 td = curthread; 483 KASSERT(td->td_epochnest == 0, ("epoch_wait() in the middle of an epoch section")); 484 thread_lock(td); 485 486 DROP_GIANT(); 487 488 old_cpu = PCPU_GET(cpuid); 489 old_pinned = td->td_pinned; 490 old_prio = td->td_priority; 491 was_bound = sched_is_bound(td); 492 sched_unbind(td); 493 td->td_pinned = 0; 494 sched_bind(td, old_cpu); 495 496 ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL); 497 498 /* restore CPU binding, if any */ 499 if (was_bound != 0) { 500 sched_bind(td, old_cpu); 501 } else { 502 /* get thread back to initial CPU, if any */ 503 if (old_pinned != 0) 504 sched_bind(td, old_cpu); 505 sched_unbind(td); 506 } 507 /* restore pinned after bind */ 508 td->td_pinned = old_pinned; 509 510 /* restore thread priority */ 511 sched_prio(td, old_prio); 512 thread_unlock(td); 513 PICKUP_GIANT(); 514 KASSERT(td->td_locks == locks, 515 ("%d residual locks held", td->td_locks - locks)); 516 } 517 518 void 519 epoch_call(epoch_t epoch, epoch_context_t ctx, void (*callback) (epoch_context_t)) 520 { 521 struct epoch_pcpu_state *eps; 522 epoch_cb_t cb; 523 524 cb = (void *)ctx; 525 526 MPASS(callback); 527 /* too early in boot to have epoch set up */ 528 if (__predict_false(epoch == NULL)) { 529 callback(ctx); 530 return; 531 } 532 MPASS(cb->ec_callback == NULL); 533 MPASS(cb->ec_link.stqe_next == NULL); 534 cb->ec_callback = callback; 535 counter_u64_add(epoch->e_frees, 1); 536 537 critical_enter(); 538 eps = epoch->e_pcpu[curcpu]; 539 STAILQ_INSERT_HEAD(&eps->eps_cblist, cb, ec_link); 540 critical_exit(); 541 } 542 543 static void 544 epoch_call_task(void *context) 545 { 546 struct epoch_pcpu_state *eps; 547 epoch_t epoch; 548 epoch_cb_t cb; 549 struct thread *td; 550 int cpu; 551 STAILQ_HEAD(, epoch_cb) tmp_head; 552 553 epoch = context; 554 STAILQ_INIT(&tmp_head); 555 td = curthread; 556 thread_lock(td); 557 CPU_FOREACH(cpu) { 558 sched_bind(td, cpu); 559 eps = epoch->e_pcpu[cpu]; 560 if (!STAILQ_EMPTY(&eps->eps_cblist)) 561 STAILQ_CONCAT(&tmp_head, &eps->eps_cblist); 562 } 563 sched_unbind(td); 564 thread_unlock(td); 565 epoch_wait(epoch); 566 567 while ((cb = STAILQ_FIRST(&tmp_head)) != NULL) { 568 STAILQ_REMOVE_HEAD(&tmp_head, ec_link); 569 cb->ec_callback((void*)cb); 570 } 571 } 572 573 int 574 in_epoch(void) 575 { 576 return (curthread->td_epochnest != 0); 577 } 578