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 #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 }