sys/kern/subr_epoch.c

   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
  53 #include <ck_epoch.h>
  54
  55 static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation");
  56
  57 /* arbitrary --- needs benchmarking */
  58 #define MAX_ADAPTIVE_SPIN 1000
  59 #define MAX_EPOCHS 64
  60
  61 CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
  62 SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information");
  63 SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats");
  64
  65 /* Stats. */
  66 static counter_u64_t block_count;
  67
  68 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW,
  69     &block_count, "# of times a thread was in an epoch when epoch_wait was called");
  70 static counter_u64_t migrate_count;
  71
  72 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW,
  73     &migrate_count, "# of times thread was migrated to another CPU in epoch_wait");
  74 static counter_u64_t turnstile_count;
  75
  76 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW,
  77     &turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait");
  78 static counter_u64_t switch_count;
  79
  80 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW,
  81     &switch_count, "# of times a thread voluntarily context switched in epoch_wait");
  82 static counter_u64_t epoch_call_count;
  83
  84 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW,
  85     &epoch_call_count, "# of times a callback was deferred");
  86 static counter_u64_t epoch_call_task_count;
  87
  88 SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW,
  89     &epoch_call_task_count, "# of times a callback task was run");
  90
  91 TAILQ_HEAD (threadlist, thread);
  92
  93 CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
  94     ck_epoch_entry_container)
  95
  96         epoch_t allepochs[MAX_EPOCHS];
  97
  98 DPCPU_DEFINE(struct grouptask, epoch_cb_task);
  99 DPCPU_DEFINE(int, epoch_cb_count);
 100
 101 static __read_mostly int domcount[MAXMEMDOM];
 102 static __read_mostly int domoffsets[MAXMEMDOM];
 103 static __read_mostly int inited;
 104 static __read_mostly int epoch_count;
 105 __read_mostly epoch_t global_epoch;
 106 __read_mostly epoch_t global_epoch_preempt;
 107
 108 static void epoch_call_task(void *context __unused);
 109
 110 #if defined(__powerpc64__) || defined(__powerpc__) || !defined(NUMA)
 111 static bool usedomains = false;
 112 #else
 113 static bool usedomains = true;
 114 #endif
 115 static void
 116 epoch_init(void *arg __unused)
 117 {
 118         int domain, cpu;
 119
 120         block_count = counter_u64_alloc(M_WAITOK);
 121         migrate_count = counter_u64_alloc(M_WAITOK);
 122         turnstile_count = counter_u64_alloc(M_WAITOK);
 123         switch_count = counter_u64_alloc(M_WAITOK);
 124         epoch_call_count = counter_u64_alloc(M_WAITOK);
 125         epoch_call_task_count = counter_u64_alloc(M_WAITOK);
 126         if (usedomains == false)
 127                 goto done;
 128         domain = 0;
 129         domoffsets[0] = 0;
 130         for (domain = 0; domain < vm_ndomains; domain++) {
 131                 domcount[domain] = CPU_COUNT(&cpuset_domain[domain]);
 132                 if (bootverbose)
 133                         printf("domcount[%d] %d\n", domain, domcount[domain]);
 134         }
 135         for (domain = 1; domain < vm_ndomains; domain++)
 136                 domoffsets[domain] = domoffsets[domain - 1] + domcount[domain - 1];
 137
 138         for (domain = 0; domain < vm_ndomains; domain++) {
 139                 if (domcount[domain] == 0) {
 140                         usedomains = false;
 141                         break;
 142                 }
 143         }
 144 done:
 145         CPU_FOREACH(cpu) {
 146                 GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0, epoch_call_task, NULL);
 147                 taskqgroup_attach_cpu(qgroup_softirq, DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, -1, "epoch call task");
 148         }
 149         inited = 1;
 150         global_epoch = epoch_alloc(0);
 151         global_epoch_preempt = epoch_alloc(EPOCH_PREEMPT);
 152 }
 153 SYSINIT(epoch, SI_SUB_TASKQ + 1, SI_ORDER_FIRST, epoch_init, NULL);
 154
 155 #if !defined(EARLY_AP_STARTUP)
 156 static void
 157 epoch_init_smp(void *dummy __unused)
 158 {
 159         inited = 2;
 160 }
 161 SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
 162 #endif
 163
 164
 165 static void
 166 epoch_init_numa(epoch_t epoch)
 167 {
 168         int domain, cpu_offset;
 169         epoch_record_t er;
 170
 171         for (domain = 0; domain < vm_ndomains; domain++) {
 172                 er = malloc_domain(sizeof(*er) * domcount[domain], M_EPOCH,
 173                     domain, M_ZERO | M_WAITOK);
 174                 epoch->e_pcpu_dom[domain] = er;
 175                 cpu_offset = domoffsets[domain];
 176                 for (int i = 0; i < domcount[domain]; i++, er++) {
 177                         epoch->e_pcpu[cpu_offset + i] = er;
 178                         ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 179                         TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 180                         er->er_cpuid = cpu_offset + i;
 181                 }
 182         }
 183 }
 184
 185 static void
 186 epoch_init_legacy(epoch_t epoch)
 187 {
 188         epoch_record_t er;
 189
 190         er = malloc(sizeof(*er) * mp_ncpus, M_EPOCH, M_ZERO | M_WAITOK);
 191         epoch->e_pcpu_dom[0] = er;
 192         for (int i = 0; i < mp_ncpus; i++, er++) {
 193                 epoch->e_pcpu[i] = er;
 194                 ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
 195                 TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
 196                 er->er_cpuid = i;
 197         }
 198 }
 199
 200 epoch_t
 201 epoch_alloc(int flags)
 202 {
 203         epoch_t epoch;
 204
 205         if (__predict_false(!inited))
 206                 panic("%s called too early in boot", __func__);
 207         epoch = malloc(sizeof(struct epoch) + mp_ncpus * sizeof(void *),
 208             M_EPOCH, M_ZERO | M_WAITOK);
 209         ck_epoch_init(&epoch->e_epoch);
 210         if (usedomains)
 211                 epoch_init_numa(epoch);
 212         else
 213                 epoch_init_legacy(epoch);
 214         MPASS(epoch_count < MAX_EPOCHS - 2);
 215         epoch->e_flags = flags;
 216         epoch->e_idx = epoch_count;
 217         allepochs[epoch_count++] = epoch;
 218         return (epoch);
 219 }
 220
 221 void
 222 epoch_free(epoch_t epoch)
 223 {
 224         int domain;
 225 #ifdef INVARIANTS
 226         struct epoch_record *er;
 227         int cpu;
 228
 229         CPU_FOREACH(cpu) {
 230                 er = epoch->e_pcpu[cpu];
 231                 MPASS(TAILQ_EMPTY(&er->er_tdlist));
 232         }
 233 #endif
 234         allepochs[epoch->e_idx] = NULL;
 235         epoch_wait(global_epoch);
 236         if (usedomains)
 237                 for (domain = 0; domain < vm_ndomains; domain++)
 238                         free_domain(epoch->e_pcpu_dom[domain], M_EPOCH);
 239         else
 240                 free(epoch->e_pcpu_dom[0], M_EPOCH);
 241         free(epoch, M_EPOCH);
 242 }
 243
 244 void
 245 epoch_enter_preempt_KBI(epoch_t epoch, epoch_tracker_t et)
 246 {
 247
 248         epoch_enter_preempt(epoch, et);
 249 }
 250
 251 void
 252 epoch_exit_preempt_KBI(epoch_t epoch, epoch_tracker_t et)
 253 {
 254
 255         epoch_exit_preempt(epoch, et);
 256 }
 257
 258 void
 259 epoch_enter_KBI(epoch_t epoch)
 260 {
 261
 262         epoch_enter(epoch);
 263 }
 264
 265 void
 266 epoch_exit_KBI(epoch_t epoch)
 267 {
 268
 269         epoch_exit(epoch);
 270 }
 271
 272 /*
 273  * epoch_block_handler_preempt is a callback from the ck code when another thread is
 274  * currently in an epoch section.
 275  */
 276 static void
 277 epoch_block_handler_preempt(struct ck_epoch *global __unused, ck_epoch_record_t *cr,
 278     void *arg __unused)
 279 {
 280         epoch_record_t record;
 281         struct thread *td, *owner, *curwaittd;
 282         struct epoch_thread *tdwait;
 283         struct turnstile *ts;
 284         struct lock_object *lock;
 285         int spincount, gen;
 286         int locksheld __unused;
 287
 288         record = __containerof(cr, struct epoch_record, er_record);
 289         td = curthread;
 290         locksheld = td->td_locks;
 291         spincount = 0;
 292         counter_u64_add(block_count, 1);
 293         if (record->er_cpuid != curcpu) {
 294                 /*
 295                  * If the head of the list is running, we can wait for it
 296                  * to remove itself from the list and thus save us the
 297                  * overhead of a migration
 298                  */
 299                 if ((tdwait = TAILQ_FIRST(&record->er_tdlist)) != NULL &&
 300                     TD_IS_RUNNING(tdwait->et_td)) {
 301                         gen = record->er_gen;
 302                         thread_unlock(td);
 303                         do {
 304                                 cpu_spinwait();
 305                         } while (tdwait == TAILQ_FIRST(&record->er_tdlist) &&
 306                             gen == record->er_gen && TD_IS_RUNNING(tdwait->et_td) &&
 307                             spincount++ < MAX_ADAPTIVE_SPIN);
 308                         thread_lock(td);
 309                         return;
 310                 }
 311                 /*
 312                  * Being on the same CPU as that of the record on which
 313                  * we need to wait allows us access to the thread
 314                  * list associated with that CPU. We can then examine the
 315                  * oldest thread in the queue and wait on its turnstile
 316                  * until it resumes and so on until a grace period
 317                  * elapses.
 318                  *
 319                  */
 320                 counter_u64_add(migrate_count, 1);
 321                 sched_bind(td, record->er_cpuid);
 322                 /*
 323                  * At this point we need to return to the ck code
 324                  * to scan to see if a grace period has elapsed.
 325                  * We can't move on to check the thread list, because
 326                  * in the meantime new threads may have arrived that
 327                  * in fact belong to a different epoch.
 328                  */
 329                 return;
 330         }
 331         /*
 332          * Try to find a thread in an epoch section on this CPU
 333          * waiting on a turnstile. Otherwise find the lowest
 334          * priority thread (highest prio value) and drop our priority
 335          * to match to allow it to run.
 336          */
 337         TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
 338                 /*
 339                  * Propagate our priority to any other waiters to prevent us
 340                  * from starving them. They will have their original priority
 341                  * restore on exit from epoch_wait().
 342                  */
 343                 curwaittd = tdwait->et_td;
 344                 if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
 345                         critical_enter();
 346                         thread_unlock(td);
 347                         thread_lock(curwaittd);
 348                         sched_prio(curwaittd, td->td_priority);
 349                         thread_unlock(curwaittd);
 350                         thread_lock(td);
 351                         critical_exit();
 352                 }
 353                 if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
 354                     ((ts = curwaittd->td_blocked) != NULL)) {
 355                         /*
 356                          * We unlock td to allow turnstile_wait to reacquire the
 357                          * the thread lock. Before unlocking it we enter a critical
 358                          * section to prevent preemption after we reenable interrupts
 359                          * by dropping the thread lock in order to prevent curwaittd
 360                          * from getting to run.
 361                          */
 362                         critical_enter();
 363                         thread_unlock(td);
 364                         owner = turnstile_lock(ts, &lock);
 365                         /*
 366                          * The owner pointer indicates that the lock succeeded. Only
 367                          * in case we hold the lock and the turnstile we locked is still
 368                          * the one that curwaittd is blocked on can we continue. Otherwise
 369                          * The turnstile pointer has been changed out from underneath
 370                          * us, as in the case where the lock holder has signalled curwaittd,
 371                          * and we need to continue.
 372                          */
 373                         if (owner != NULL && ts == curwaittd->td_blocked) {
 374                                 MPASS(TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd));
 375                                 critical_exit();
 376                                 turnstile_wait(ts, owner, curwaittd->td_tsqueue);
 377                                 counter_u64_add(turnstile_count, 1);
 378                                 thread_lock(td);
 379                                 return;
 380                         } else if (owner != NULL)
 381                                 turnstile_unlock(ts, lock);
 382                         thread_lock(td);
 383                         critical_exit();
 384                         KASSERT(td->td_locks == locksheld,
 385                             ("%d extra locks held", td->td_locks - locksheld));
 386                 }
 387         }
 388         /*
 389          * We didn't find any threads actually blocked on a lock
 390          * so we have nothing to do except context switch away.
 391          */
 392         counter_u64_add(switch_count, 1);
 393         mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
 394
 395         /*
 396          * Release the thread lock while yielding to
 397          * allow other threads to acquire the lock
 398          * pointed to by TDQ_LOCKPTR(td). Else a
 399          * deadlock like situation might happen. (HPS)
 400          */
 401         thread_unlock(td);
 402         thread_lock(td);
 403 }
 404
 405 void
 406 epoch_wait_preempt(epoch_t epoch)
 407 {
 408         struct thread *td;
 409         int was_bound;
 410         int old_cpu;
 411         int old_pinned;
 412         u_char old_prio;
 413         int locks __unused;
 414
 415         MPASS(cold || epoch != NULL);
 416         INIT_CHECK(epoch);
 417         td = curthread;
 418 #ifdef INVARIANTS
 419         locks = curthread->td_locks;
 420         MPASS(epoch->e_flags & EPOCH_PREEMPT);
 421         if ((epoch->e_flags & EPOCH_LOCKED) == 0)
 422                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 423                     "epoch_wait() can be long running");
 424         KASSERT(td->td_epochnest == 0, ("epoch_wait() in the middle of an epoch section"));
 425 #endif
 426         thread_lock(td);
 427         DROP_GIANT();
 428
 429         old_cpu = PCPU_GET(cpuid);
 430         old_pinned = td->td_pinned;
 431         old_prio = td->td_priority;
 432         was_bound = sched_is_bound(td);
 433         sched_unbind(td);
 434         td->td_pinned = 0;
 435         sched_bind(td, old_cpu);
 436
 437         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt, NULL);
 438
 439         /* restore CPU binding, if any */
 440         if (was_bound != 0) {
 441                 sched_bind(td, old_cpu);
 442         } else {
 443                 /* get thread back to initial CPU, if any */
 444                 if (old_pinned != 0)
 445                         sched_bind(td, old_cpu);
 446                 sched_unbind(td);
 447         }
 448         /* restore pinned after bind */
 449         td->td_pinned = old_pinned;
 450
 451         /* restore thread priority */
 452         sched_prio(td, old_prio);
 453         thread_unlock(td);
 454         PICKUP_GIANT();
 455         KASSERT(td->td_locks == locks,
 456             ("%d residual locks held", td->td_locks - locks));
 457 }
 458
 459 static void
 460 epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
 461     void *arg __unused)
 462 {
 463         cpu_spinwait();
 464 }
 465
 466 void
 467 epoch_wait(epoch_t epoch)
 468 {
 469
 470         MPASS(cold || epoch != NULL);
 471         INIT_CHECK(epoch);
 472         MPASS(epoch->e_flags == 0);
 473         critical_enter();
 474         ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
 475         critical_exit();
 476 }
 477
 478 void
 479 epoch_call(epoch_t epoch, epoch_context_t ctx, void (*callback) (epoch_context_t))
 480 {
 481         epoch_record_t er;
 482         ck_epoch_entry_t *cb;
 483
 484         cb = (void *)ctx;
 485
 486         MPASS(callback);
 487         /* too early in boot to have epoch set up */
 488         if (__predict_false(epoch == NULL))
 489                 goto boottime;
 490 #if !defined(EARLY_AP_STARTUP)
 491         if (__predict_false(inited < 2))
 492                 goto boottime;
 493 #endif
 494
 495         critical_enter();
 496         *DPCPU_PTR(epoch_cb_count) += 1;
 497         er = epoch->e_pcpu[curcpu];
 498         ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
 499         critical_exit();
 500         return;
 501 boottime:
 502         callback(ctx);
 503 }
 504
 505 static void
 506 epoch_call_task(void *arg __unused)
 507 {
 508         ck_stack_entry_t *cursor, *head, *next;
 509         ck_epoch_record_t *record;
 510         epoch_t epoch;
 511         ck_stack_t cb_stack;
 512         int i, npending, total;
 513
 514         ck_stack_init(&cb_stack);
 515         critical_enter();
 516         epoch_enter(global_epoch);
 517         for (total = i = 0; i < epoch_count; i++) {
 518                 if (__predict_false((epoch = allepochs[i]) == NULL))
 519                         continue;
 520                 record = &epoch->e_pcpu[curcpu]->er_record;
 521                 if ((npending = record->n_pending) == 0)
 522                         continue;
 523                 ck_epoch_poll_deferred(record, &cb_stack);
 524                 total += npending - record->n_pending;
 525         }
 526         epoch_exit(global_epoch);
 527         *DPCPU_PTR(epoch_cb_count) -= total;
 528         critical_exit();
 529
 530         counter_u64_add(epoch_call_count, total);
 531         counter_u64_add(epoch_call_task_count, 1);
 532
 533         head = ck_stack_batch_pop_npsc(&cb_stack);
 534         for (cursor = head; cursor != NULL; cursor = next) {
 535                 struct ck_epoch_entry *entry =
 536                 ck_epoch_entry_container(cursor);
 537
 538                 next = CK_STACK_NEXT(cursor);
 539                 entry->function(entry);
 540         }
 541 }
 542
 543 int
 544 in_epoch_verbose(epoch_t epoch, int dump_onfail)
 545 {
 546         struct epoch_thread *tdwait;
 547         struct thread *td;
 548         epoch_record_t er;
 549
 550         td = curthread;
 551         if (td->td_epochnest == 0)
 552                 return (0);
 553         if (__predict_false((epoch) == NULL))
 554                 return (0);
 555         critical_enter();
 556         er = epoch->e_pcpu[curcpu];
 557         TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 558                 if (tdwait->et_td == td) {
 559                         critical_exit();
 560                         return (1);
 561                 }
 562 #ifdef INVARIANTS
 563         if (dump_onfail) {
 564                 MPASS(td->td_pinned);
 565                 printf("cpu: %d id: %d\n", curcpu, td->td_tid);
 566                 TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
 567                         printf("td_tid: %d ", tdwait->et_td->td_tid);
 568                 printf("\n");
 569         }
 570 #endif
 571         critical_exit();
 572         return (0);
 573 }
 574
 575 int
 576 in_epoch(epoch_t epoch)
 577 {
 578         return (in_epoch_verbose(epoch, 0));
 579 }
 580
 581 void
 582 epoch_adjust_prio(struct thread *td, u_char prio)
 583 {
 584         thread_lock(td);
 585         sched_prio(td, prio);
 586         thread_unlock(td);
 587 }