fs/zfs/vdev_queue.c

	vdev_queue.c revision c3a66015199e1814c2af8f7e6929af2004302e7e
/*
 * 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.
 */

/*
 * Copyright (c) 2012 by Delphix. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/vdev_impl.h>
#include <sys/spa_impl.h>
#include <sys/zio.h>
#include <sys/avl.h>

/*
 * These tunables are for performance analysis.
 */
/*
 * zfs_vdev_max_pending is the maximum number of i/os concurrently
 * pending to each device.  zfs_vdev_min_pending is the initial number
 * of i/os pending to each device (before it starts ramping up to
 * max_pending).
 */
int zfs_vdev_max_pending = 10;
int zfs_vdev_min_pending = 4;

/* deadline = pri + ddi_get_lbolt64() >> time_shift) */
int zfs_vdev_time_shift = 6;

/* exponential I/O issue ramp-up rate */
int zfs_vdev_ramp_rate = 2;

/*
 * To reduce IOPs, we aggregate small adjacent I/Os into one large I/O.
 * For read I/Os, we also aggregate across small adjacency gaps; for writes
 * we include spans of optional I/Os to aid aggregation at the disk even when
 * they aren't able to help us aggregate at this level.
 */
int zfs_vdev_aggregation_limit = SPA_MAXBLOCKSIZE;
int zfs_vdev_read_gap_limit = 32 << 10;
int zfs_vdev_write_gap_limit = 4 << 10;

/*
 * Virtual device vector for disk I/O scheduling.
 */
int
vdev_queue_deadline_compare(const void *x1, const void *x2)
{
    const zio_t *z1 = x1;
    const zio_t *z2 = x2;

    if (z1->io_deadline < z2->io_deadline)
        return (-1);
    if (z1->io_deadline > z2->io_deadline)
        return (1);

    if (z1->io_offset < z2->io_offset)
        return (-1);
    if (z1->io_offset > z2->io_offset)
        return (1);

    if (z1 < z2)
        return (-1);
    if (z1 > z2)
        return (1);

    return (0);
}

int
vdev_queue_offset_compare(const void *x1, const void *x2)
{
    const zio_t *z1 = x1;
    const zio_t *z2 = x2;

    if (z1->io_offset < z2->io_offset)
        return (-1);
    if (z1->io_offset > z2->io_offset)
        return (1);

    if (z1 < z2)
        return (-1);
    if (z1 > z2)
        return (1);

    return (0);
}

void
vdev_queue_init(vdev_t *vd)
{
    vdev_queue_t *vq = &vd->vdev_queue;

    mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);

    avl_create(&vq->vq_deadline_tree, vdev_queue_deadline_compare,
        sizeof (zio_t), offsetof(struct zio, io_deadline_node));

    avl_create(&vq->vq_read_tree, vdev_queue_offset_compare,
        sizeof (zio_t), offsetof(struct zio, io_offset_node));

    avl_create(&vq->vq_write_tree, vdev_queue_offset_compare,
        sizeof (zio_t), offsetof(struct zio, io_offset_node));

    avl_create(&vq->vq_pending_tree, vdev_queue_offset_compare,
        sizeof (zio_t), offsetof(struct zio, io_offset_node));
}

void
vdev_queue_fini(vdev_t *vd)
{
    vdev_queue_t *vq = &vd->vdev_queue;

    avl_destroy(&vq->vq_deadline_tree);
    avl_destroy(&vq->vq_read_tree);
    avl_destroy(&vq->vq_write_tree);
    avl_destroy(&vq->vq_pending_tree);

    mutex_destroy(&vq->vq_lock);
}

static void
vdev_queue_io_add(vdev_queue_t *vq, zio_t *zio)
{
    spa_t *spa = zio->io_spa;
    avl_add(&vq->vq_deadline_tree, zio);
    avl_add(zio->io_vdev_tree, zio);

    if (spa->spa_iokstat != NULL) {
        mutex_enter(&spa->spa_iokstat_lock);
        kstat_waitq_enter(spa->spa_iokstat->ks_data);
        mutex_exit(&spa->spa_iokstat_lock);
    }
}

static void
vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
{
    spa_t *spa = zio->io_spa;
    avl_remove(&vq->vq_deadline_tree, zio);
    avl_remove(zio->io_vdev_tree, zio);

    if (spa->spa_iokstat != NULL) {
        mutex_enter(&spa->spa_iokstat_lock);
        kstat_waitq_exit(spa->spa_iokstat->ks_data);
        mutex_exit(&spa->spa_iokstat_lock);
    }
}

static void
vdev_queue_pending_add(vdev_queue_t *vq, zio_t *zio)
{
    spa_t *spa = zio->io_spa;
    avl_add(&vq->vq_pending_tree, zio);
    if (spa->spa_iokstat != NULL) {
        mutex_enter(&spa->spa_iokstat_lock);
        kstat_runq_enter(spa->spa_iokstat->ks_data);
        mutex_exit(&spa->spa_iokstat_lock);
    }
}

static void
vdev_queue_pending_remove(vdev_queue_t *vq, zio_t *zio)
{
    spa_t *spa = zio->io_spa;
    avl_remove(&vq->vq_pending_tree, zio);
    if (spa->spa_iokstat != NULL) {
        kstat_io_t *ksio = spa->spa_iokstat->ks_data;

        mutex_enter(&spa->spa_iokstat_lock);
        kstat_runq_exit(spa->spa_iokstat->ks_data);
        if (zio->io_type == ZIO_TYPE_READ) {
            ksio->reads++;
            ksio->nread += zio->io_size;
        } else if (zio->io_type == ZIO_TYPE_WRITE) {
            ksio->writes++;
            ksio->nwritten += zio->io_size;
        }
        mutex_exit(&spa->spa_iokstat_lock);
    }
}

static void
vdev_queue_agg_io_done(zio_t *aio)
{
    zio_t *pio;

    while ((pio = zio_walk_parents(aio)) != NULL)
        if (aio->io_type == ZIO_TYPE_READ)
            bcopy((char *)aio->io_data + (pio->io_offset -
                aio->io_offset), pio->io_data, pio->io_size);

    zio_buf_free(aio->io_data, aio->io_size);
}

/*
 * Compute the range spanned by two i/os, which is the endpoint of the last
 * (lio->io_offset + lio->io_size) minus start of the first (fio->io_offset).
 * Conveniently, the gap between fio and lio is given by -IO_SPAN(lio, fio);
 * thus fio and lio are adjacent if and only if IO_SPAN(lio, fio) == 0.
 */
#define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
#define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))

static zio_t *
vdev_queue_io_to_issue(vdev_queue_t *vq, uint64_t pending_limit)
{
    zio_t *fio, *lio, *aio, *dio, *nio, *mio;
    avl_tree_t *t;
    int flags;
    uint64_t maxspan = zfs_vdev_aggregation_limit;
    uint64_t maxgap;
    int stretch;

again:
    ASSERT(MUTEX_HELD(&vq->vq_lock));

    if (avl_numnodes(&vq->vq_pending_tree) >= pending_limit ||
        avl_numnodes(&vq->vq_deadline_tree) == 0)
        return (NULL);

    fio = lio = avl_first(&vq->vq_deadline_tree);

    t = fio->io_vdev_tree;
    flags = fio->io_flags & ZIO_FLAG_AGG_INHERIT;
    maxgap = (t == &vq->vq_read_tree) ? zfs_vdev_read_gap_limit : 0;

    if (!(flags & ZIO_FLAG_DONT_AGGREGATE)) {
        /*
         * We can aggregate I/Os that are sufficiently adjacent and of
         * the same flavor, as expressed by the AGG_INHERIT flags.
         * The latter requirement is necessary so that certain
         * attributes of the I/O, such as whether it's a normal I/O
         * or a scrub/resilver, can be preserved in the aggregate.
         * We can include optional I/Os, but don't allow them
         * to begin a range as they add no benefit in that situation.
         */

        /*
         * We keep track of the last non-optional I/O.
         */
        mio = (fio->io_flags & ZIO_FLAG_OPTIONAL) ? NULL : fio;

        /*
         * Walk backwards through sufficiently contiguous I/Os
         * recording the last non-option I/O.
         */
        while ((dio = AVL_PREV(t, fio)) != NULL &&
            (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
            IO_SPAN(dio, lio) <= maxspan &&
            IO_GAP(dio, fio) <= maxgap) {
            fio = dio;
            if (mio == NULL && !(fio->io_flags & ZIO_FLAG_OPTIONAL))
                mio = fio;
        }

        /*
         * Skip any initial optional I/Os.
         */
        while ((fio->io_flags & ZIO_FLAG_OPTIONAL) && fio != lio) {
            fio = AVL_NEXT(t, fio);
            ASSERT(fio != NULL);
        }

        /*
         * Walk forward through sufficiently contiguous I/Os.
         */
        while ((dio = AVL_NEXT(t, lio)) != NULL &&
            (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
            IO_SPAN(fio, dio) <= maxspan &&
            IO_GAP(lio, dio) <= maxgap) {
            lio = dio;
            if (!(lio->io_flags & ZIO_FLAG_OPTIONAL))
                mio = lio;
        }

        /*
         * Now that we've established the range of the I/O aggregation
         * we must decide what to do with trailing optional I/Os.
         * For reads, there's nothing to do. While we are unable to
         * aggregate further, it's possible that a trailing optional
         * I/O would allow the underlying device to aggregate with
         * subsequent I/Os. We must therefore determine if the next
         * non-optional I/O is close enough to make aggregation
         * worthwhile.
         */
        stretch = B_FALSE;
        if (t != &vq->vq_read_tree && mio != NULL) {
            nio = lio;
            while ((dio = AVL_NEXT(t, nio)) != NULL &&
                IO_GAP(nio, dio) == 0 &&
                IO_GAP(mio, dio) <= zfs_vdev_write_gap_limit) {
                nio = dio;
                if (!(nio->io_flags & ZIO_FLAG_OPTIONAL)) {
                    stretch = B_TRUE;
                    break;
                }
            }
        }

        if (stretch) {
            /* This may be a no-op. */
            VERIFY((dio = AVL_NEXT(t, lio)) != NULL);
            dio->io_flags &= ~ZIO_FLAG_OPTIONAL;
        } else {
            while (lio != mio && lio != fio) {
                ASSERT(lio->io_flags & ZIO_FLAG_OPTIONAL);
                lio = AVL_PREV(t, lio);
                ASSERT(lio != NULL);
            }
        }
    }

    if (fio != lio) {
        uint64_t size = IO_SPAN(fio, lio);
        ASSERT(size <= zfs_vdev_aggregation_limit);

        aio = zio_vdev_delegated_io(fio->io_vd, fio->io_offset,
            zio_buf_alloc(size), size, fio->io_type, ZIO_PRIORITY_AGG,
            flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
            vdev_queue_agg_io_done, NULL);
        aio->io_timestamp = fio->io_timestamp;

        nio = fio;
        do {
            dio = nio;
            nio = AVL_NEXT(t, dio);
            ASSERT(dio->io_type == aio->io_type);
            ASSERT(dio->io_vdev_tree == t);

            if (dio->io_flags & ZIO_FLAG_NODATA) {
                ASSERT(dio->io_type == ZIO_TYPE_WRITE);
                bzero((char *)aio->io_data + (dio->io_offset -
                    aio->io_offset), dio->io_size);
            } else if (dio->io_type == ZIO_TYPE_WRITE) {
                bcopy(dio->io_data, (char *)aio->io_data +
                    (dio->io_offset - aio->io_offset),
                    dio->io_size);
            }

            zio_add_child(dio, aio);
            vdev_queue_io_remove(vq, dio);
            zio_vdev_io_bypass(dio);
            zio_execute(dio);
        } while (dio != lio);

        vdev_queue_pending_add(vq, aio);

        return (aio);
    }

    ASSERT(fio->io_vdev_tree == t);
    vdev_queue_io_remove(vq, fio);

    /*
     * If the I/O is or was optional and therefore has no data, we need to
     * simply discard it. We need to drop the vdev queue's lock to avoid a
     * deadlock that we could encounter since this I/O will complete
     * immediately.
     */
    if (fio->io_flags & ZIO_FLAG_NODATA) {
        mutex_exit(&vq->vq_lock);
        zio_vdev_io_bypass(fio);
        zio_execute(fio);
        mutex_enter(&vq->vq_lock);
        goto again;
    }

    vdev_queue_pending_add(vq, fio);

    return (fio);
}

zio_t *
vdev_queue_io(zio_t *zio)
{
    vdev_queue_t *vq = &zio->io_vd->vdev_queue;
    zio_t *nio;

    ASSERT(zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE);

    if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
        return (zio);

    zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;

    if (zio->io_type == ZIO_TYPE_READ)
        zio->io_vdev_tree = &vq->vq_read_tree;
    else
        zio->io_vdev_tree = &vq->vq_write_tree;

    mutex_enter(&vq->vq_lock);

    zio->io_timestamp = ddi_get_lbolt64();
    zio->io_deadline = (zio->io_timestamp >> zfs_vdev_time_shift) +
        zio->io_priority;

    vdev_queue_io_add(vq, zio);

    nio = vdev_queue_io_to_issue(vq, zfs_vdev_min_pending);

    mutex_exit(&vq->vq_lock);

    if (nio == NULL)
        return (NULL);

    if (nio->io_done == vdev_queue_agg_io_done) {
        zio_nowait(nio);
        return (NULL);
    }

    return (nio);
}

void
vdev_queue_io_done(zio_t *zio)
{
    vdev_queue_t *vq = &zio->io_vd->vdev_queue;

    if (zio_injection_enabled)
        delay(SEC_TO_TICK(zio_handle_io_delay(zio)));

    mutex_enter(&vq->vq_lock);

    vdev_queue_pending_remove(vq, zio);

    vq->vq_io_complete_ts = ddi_get_lbolt64();
    vq->vq_io_delta_ts = vq->vq_io_complete_ts - zio->io_timestamp;

    for (int i = 0; i < zfs_vdev_ramp_rate; i++) {
        zio_t *nio = vdev_queue_io_to_issue(vq, zfs_vdev_max_pending);
        if (nio == NULL)
            break;
        mutex_exit(&vq->vq_lock);
        if (nio->io_done == vdev_queue_agg_io_done) {
            zio_nowait(nio);
        } else {
            zio_vdev_io_reissue(nio);
            zio_execute(nio);
        }
        mutex_enter(&vq->vq_lock);
    }

    mutex_exit(&vq->vq_lock);
}