vdev_queue.c

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/*
 * 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 <sys/vdev_impl.h>
#include <sys/zio.h>
#include <sys/avl.h>

/* These tunables are for performance analysis. */
int zfs_vdev_max_pending = 10;

int zfs_vdev_min_pending = 4;

int zfs_vdev_time_shift = 6;

int zfs_vdev_ramp_rate = 2;

int zfs_vdev_aggregation_limit = SPA_MAXBLOCKSIZE;
int zfs_vdev_read_gap_limit = 32 << 10;
int zfs_vdev_write_gap_limit = 4 << 10;
SYSCTL_DECL(_vfs_zfs_vdev);
TUNABLE_INT("vfs.zfs.vdev.max_pending", &zfs_vdev_max_pending);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, max_pending, CTLFLAG_RW,
    &zfs_vdev_max_pending, 0, "Maximum I/O requests pending on each device");
TUNABLE_INT("vfs.zfs.vdev.min_pending", &zfs_vdev_min_pending);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, min_pending, CTLFLAG_RW,
    &zfs_vdev_min_pending, 0,
    "Initial number of I/O requests pending to each device");
TUNABLE_INT("vfs.zfs.vdev.time_shift", &zfs_vdev_time_shift);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, time_shift, CTLFLAG_RW,
    &zfs_vdev_time_shift, 0, "Used for calculating I/O request deadline");
TUNABLE_INT("vfs.zfs.vdev.ramp_rate", &zfs_vdev_ramp_rate);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, ramp_rate, CTLFLAG_RW,
    &zfs_vdev_ramp_rate, 0, "Exponential I/O issue ramp-up rate");
TUNABLE_INT("vfs.zfs.vdev.aggregation_limit", &zfs_vdev_aggregation_limit);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, aggregation_limit, CTLFLAG_RW,
    &zfs_vdev_aggregation_limit, 0,
    "I/O requests are aggregated up to this size");
TUNABLE_INT("vfs.zfs.vdev.read_gap_limit", &zfs_vdev_read_gap_limit);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, read_gap_limit, CTLFLAG_RW,
    &zfs_vdev_read_gap_limit, 0,
    "Acceptable gap between two reads being aggregated");
TUNABLE_INT("vfs.zfs.vdev.write_gap_limit", &zfs_vdev_write_gap_limit);
SYSCTL_INT(_vfs_zfs_vdev, OID_AUTO, write_gap_limit, CTLFLAG_RW,
    &zfs_vdev_write_gap_limit, 0,
    "Acceptable gap between two writes being aggregated");

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)
{
        avl_add(&vq->vq_deadline_tree, zio);
        avl_add(zio->io_vdev_tree, zio);
}

static void
vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
{
        avl_remove(&vq->vq_deadline_tree, zio);
        avl_remove(zio->io_vdev_tree, zio);
}

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);
}

#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);

                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);

                avl_add(&vq->vq_pending_tree, 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;
        }

        avl_add(&vq->vq_pending_tree, 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_deadline = (ddi_get_lbolt64() >> 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;

        mutex_enter(&vq->vq_lock);

        avl_remove(&vq->vq_pending_tree, zio);

        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);
}