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taskq.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/zfs_context.h>
#include <pthread.h>
#include <syslog.h>

int taskq_now;
taskq_t *system_taskq;

typedef struct task {
      struct task *task_next;
      struct task *task_prev;
      task_func_t *task_func;
      void        *task_arg;
} task_t;

#define     TASKQ_ACTIVE      0x00010000

struct taskq {
      const char  *name;
      kmutex_t    tq_lock;
      krwlock_t   tq_threadlock;
      kcondvar_t  tq_dispatch_cv;
      kcondvar_t  tq_wait_cv;
      pthread_t   *tq_threadlist;
      int         tq_flags;
      int         tq_active;
      int         tq_nthreads;
      int         tq_nalloc;
      int         tq_minalloc;
      int         tq_maxalloc;
      task_t            *tq_freelist;
      task_t            tq_task;
};

static task_t *
task_alloc(taskq_t *tq, int tqflags)
{
      task_t *t;

      if ((t = tq->tq_freelist) != NULL && tq->tq_nalloc >= tq->tq_minalloc) {
            tq->tq_freelist = t->task_next;
      } else {
            mutex_exit(&tq->tq_lock);
            if (tq->tq_nalloc >= tq->tq_maxalloc) {
                  if (!(tqflags & KM_SLEEP)) {
                        mutex_enter(&tq->tq_lock);
                        syslog(LOG_WARNING,
                            "task_alloc failure name %s nalloc %d maxalloc %d",
                            tq->name,tq->tq_nalloc,tq->tq_maxalloc);
                        return (NULL);
                  }
                  /*
                   * We don't want to exceed tq_maxalloc, but we can't
                   * wait for other tasks to complete (and thus free up
                   * task structures) without risking deadlock with
                   * the caller.  So, we just delay for one second
                   * to throttle the allocation rate.
                   */
                  syslog(LOG_WARNING,
                      "task_alloc: allocation out of limits, name %s nalloc %d maxalloc %d",
                      tq->name,tq->tq_nalloc,tq->tq_maxalloc);
                  delay(hz);
            }
            t = kmem_alloc(sizeof (task_t), tqflags);
            mutex_enter(&tq->tq_lock);
            if (t != NULL)
                  tq->tq_nalloc++;
      }
      return (t);
}

static void
task_free(taskq_t *tq, task_t *t)
{
      if (tq->tq_nalloc <= tq->tq_minalloc) {
            t->task_next = tq->tq_freelist;
            tq->tq_freelist = t;
      } else {
            tq->tq_nalloc--;
            mutex_exit(&tq->tq_lock);
            kmem_free(t, sizeof (task_t));
            mutex_enter(&tq->tq_lock);
      }
}

taskqid_t
taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t tqflags)
{
      task_t *t;

      if (taskq_now) {
            func(arg);
            return (1);
      }

      mutex_enter(&tq->tq_lock);
      ASSERT(tq->tq_flags & TASKQ_ACTIVE);
      if ((t = task_alloc(tq, tqflags)) == NULL) {
            mutex_exit(&tq->tq_lock);
            return (0);
      }
      t->task_next = &tq->tq_task;
      t->task_prev = tq->tq_task.task_prev;
      t->task_next->task_prev = t;
      t->task_prev->task_next = t;
      t->task_func = func;
      t->task_arg = arg;
      cv_signal(&tq->tq_dispatch_cv);
      mutex_exit(&tq->tq_lock);
      return (1);
}

void
taskq_wait(taskq_t *tq)
{
      mutex_enter(&tq->tq_lock);
      while (tq->tq_task.task_next != &tq->tq_task || tq->tq_active != 0)
            cv_wait(&tq->tq_wait_cv, &tq->tq_lock);
      mutex_exit(&tq->tq_lock);
}

static void *
taskq_thread(void *arg)
{
      taskq_t *tq = arg;
      task_t *t;

      mutex_enter(&tq->tq_lock);
      while (tq->tq_flags & TASKQ_ACTIVE) {
            if ((t = tq->tq_task.task_next) == &tq->tq_task) {
                  if (--tq->tq_active == 0)
                        cv_broadcast(&tq->tq_wait_cv);
                  cv_wait(&tq->tq_dispatch_cv, &tq->tq_lock);
                  tq->tq_active++;
                  continue;
            }
            t->task_prev->task_next = t->task_next;
            t->task_next->task_prev = t->task_prev;
            mutex_exit(&tq->tq_lock);

            rw_enter(&tq->tq_threadlock, RW_READER);
            t->task_func(t->task_arg);
            rw_exit(&tq->tq_threadlock);

            mutex_enter(&tq->tq_lock);
            task_free(tq, t);
      }
      tq->tq_nthreads--;
      cv_broadcast(&tq->tq_wait_cv);
      mutex_exit(&tq->tq_lock);
      return (NULL);
}

/*ARGSUSED*/
taskq_t *
taskq_create(const char *name, int nthreads, pri_t pri,
      int minalloc, int maxalloc, uint_t flags)
{
      taskq_t *tq = kmem_zalloc(sizeof (taskq_t), KM_SLEEP);
      int t;

      if (flags & TASKQ_THREADS_CPU_PCT) {
            int pct;
            ASSERT3S(nthreads, >=, 0);
            ASSERT3S(nthreads, <=, 100);
            pct = MIN(nthreads, 100);
            pct = MAX(pct, 0);

            nthreads = (sysconf(_SC_NPROCESSORS_ONLN) * pct) / 100;
            nthreads = MAX(nthreads, 1);  /* need at least 1 thread */
      } else {
            ASSERT3S(nthreads, >=, 1);
      }

      rw_init(&tq->tq_threadlock, NULL, RW_DEFAULT, NULL);
      mutex_init(&tq->tq_lock, NULL, MUTEX_DEFAULT, NULL);
      cv_init(&tq->tq_dispatch_cv, NULL, CV_DEFAULT, NULL);
      cv_init(&tq->tq_wait_cv, NULL, CV_DEFAULT, NULL);
      tq->name = name;
      tq->tq_flags = flags | TASKQ_ACTIVE;
      tq->tq_active = nthreads;
      tq->tq_nthreads = nthreads;
      tq->tq_minalloc = minalloc;
      tq->tq_maxalloc = maxalloc;
      tq->tq_task.task_next = &tq->tq_task;
      tq->tq_task.task_prev = &tq->tq_task;
      tq->tq_threadlist = kmem_alloc(nthreads * sizeof (pthread_t), KM_SLEEP);

      if (flags & TASKQ_PREPOPULATE) {
            mutex_enter(&tq->tq_lock);
            while (minalloc-- > 0)
                  task_free(tq, task_alloc(tq, KM_SLEEP));
            mutex_exit(&tq->tq_lock);
      }

      for (t = 0; t < nthreads; t++)
            pthread_create(&tq->tq_threadlist[t], NULL, taskq_thread, tq);

      return (tq);
}

void
taskq_destroy(taskq_t *tq)
{
      int t;
      int nthreads = tq->tq_nthreads;

      taskq_wait(tq);

      mutex_enter(&tq->tq_lock);

      tq->tq_flags &= ~TASKQ_ACTIVE;
      cv_broadcast(&tq->tq_dispatch_cv);

      while (tq->tq_nthreads != 0)
            cv_wait(&tq->tq_wait_cv, &tq->tq_lock);

      tq->tq_minalloc = 0;
      while (tq->tq_nalloc != 0) {
            ASSERT(tq->tq_freelist != NULL);
            task_free(tq, task_alloc(tq, KM_SLEEP));
      }

      mutex_exit(&tq->tq_lock);

      for (t = 0; t < nthreads; t++)
            (void) pthread_join(tq->tq_threadlist[t], NULL);

      kmem_free(tq->tq_threadlist, nthreads * sizeof (pthread_t));

      rw_destroy(&tq->tq_threadlock);
      mutex_destroy(&tq->tq_lock);
      cv_destroy(&tq->tq_dispatch_cv);
      cv_destroy(&tq->tq_wait_cv);

      kmem_free(tq, sizeof (taskq_t));
}

int
taskq_member(taskq_t *tq, kthread_t *t)
{
      int i;

      if (taskq_now)
            return (1);

      for (i = 0; i < tq->tq_nthreads; i++)
            if (tq->tq_threadlist[i] == (pthread_t)(uintptr_t)t)
                  return (1);

      return (0);
}

void
system_taskq_init(void)
{
      system_taskq = taskq_create("system_taskq", 64, minclsyspri, 4, 512,
          TASKQ_DYNAMIC | TASKQ_PREPOPULATE);
}

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