libzpool/common/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 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/zfs_context.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 {
    kmutex_t    tq_lock;
    krwlock_t   tq_threadlock;
    kcondvar_t  tq_dispatch_cv;
    kcondvar_t  tq_wait_cv;
    thread_t    *tq_threadlist;
    int     tq_flags;
    int     tq_active;
    int     tq_nthreads;
    int     tq_nalloc;
    int     tq_minalloc;
    int     tq_maxalloc;
    kcondvar_t  tq_maxalloc_cv;
    int     tq_maxalloc_wait;
    task_t      *tq_freelist;
    task_t      tq_task;
};

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

again:  if ((t = tq->tq_freelist) != NULL && tq->tq_nalloc >= tq->tq_minalloc) {
        tq->tq_freelist = t->task_next;
    } else {
        if (tq->tq_nalloc >= tq->tq_maxalloc) {
            if (!(tqflags & KM_SLEEP))
                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. If we have tasks
             * complete before one second timeout expires then
             * taskq_ent_free will signal us and we will
             * immediately retry the allocation.
             */
            tq->tq_maxalloc_wait++;
            rv = cv_timedwait(&tq->tq_maxalloc_cv,
                &tq->tq_lock, ddi_get_lbolt() + hz);
            tq->tq_maxalloc_wait--;
            if (rv > 0)
                goto again;     /* signaled */
        }
        mutex_exit(&tq->tq_lock);

        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);
    }

    if (tq->tq_maxalloc_wait)
        cv_signal(&tq->tq_maxalloc_cv);
}

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);
    }
    if (tqflags & TQ_FRONT) {
        t->task_next = tq->tq_task.task_next;
        t->task_prev = &tq->tq_task;
    } else {
        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);
    cv_init(&tq->tq_maxalloc_cv, NULL, CV_DEFAULT, NULL);
    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 (thread_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++)
        (void) thr_create(0, 0, taskq_thread,
            tq, THR_BOUND, &tq->tq_threadlist[t]);

    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) thr_join(tq->tq_threadlist[t], NULL, NULL);

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

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

    kmem_free(tq, sizeof (taskq_t));
}

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

    if (taskq_now)
        return (1);

    for (i = 0; i < tq->tq_nthreads; i++)
        if (tq->tq_threadlist[i] == (thread_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);
}

void
system_taskq_fini(void)
{
    taskq_destroy(system_taskq);
    system_taskq = NULL; /* defensive */
}