Illumos #4045 write throttle & i/o scheduler performance work

[mirror_zfs.git] / module / zfs / vdev_mirror.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.
 */

/*
 * Copyright (c) 2013 by Delphix. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/vdev_impl.h>
#include <sys/zio.h>
#include <sys/fs/zfs.h>

/*
 * Virtual device vector for mirroring.
 */

typedef struct mirror_child {
        vdev_t          *mc_vd;
        uint64_t        mc_offset;
        int             mc_error;
        int             mc_pending;
        uint8_t         mc_tried;
        uint8_t         mc_skipped;
        uint8_t         mc_speculative;
} mirror_child_t;

typedef struct mirror_map {
        int             mm_children;
        int             mm_replacing;
        int             mm_preferred;
        int             mm_root;
        mirror_child_t  mm_child[1];
} mirror_map_t;

/*
 * When the children are equally busy queue incoming requests to a single
 * child for N microseconds.  This is done to maximize the likelihood that
 * the Linux elevator will be able to merge requests while it is plugged.
 * Otherwise, requests are queued to the least busy device.
 *
 * For rotational disks the Linux elevator will plug for 10ms which is
 * why zfs_vdev_mirror_switch_us is set to 10ms by default.  For non-
 * rotational disks the elevator will not plug, but 10ms is still a small
 * enough value that the requests will get spread over all the children.
 *
 * For fast SSDs it may make sense to decrease zfs_vdev_mirror_switch_us
 * significantly to bound the worst case latencies.  It would probably be
 * ideal to calculate a decaying average of the last observed latencies and
 * use that to dynamically adjust the zfs_vdev_mirror_switch_us time.
 */
int zfs_vdev_mirror_switch_us = 10000;

static void
vdev_mirror_map_free(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;

        kmem_free(mm, offsetof(mirror_map_t, mm_child[mm->mm_children]));
}

static const zio_vsd_ops_t vdev_mirror_vsd_ops = {
        vdev_mirror_map_free,
        zio_vsd_default_cksum_report
};

static int
vdev_mirror_pending(vdev_t *vd)
{
        return (avl_numnodes(&vd->vdev_queue.vq_active_tree));
}

/*
 * Avoid inlining the function to keep vdev_mirror_io_start(), which
 * is this functions only caller, as small as possible on the stack.
 */
noinline static mirror_map_t *
vdev_mirror_map_alloc(zio_t *zio)
{
        mirror_map_t *mm = NULL;
        mirror_child_t *mc;
        vdev_t *vd = zio->io_vd;
        int c, d;

        if (vd == NULL) {
                dva_t *dva = zio->io_bp->blk_dva;
                spa_t *spa = zio->io_spa;

                c = BP_GET_NDVAS(zio->io_bp);

                mm = kmem_zalloc(offsetof(mirror_map_t, mm_child[c]),
                    KM_PUSHPAGE);
                mm->mm_children = c;
                mm->mm_replacing = B_FALSE;
                mm->mm_preferred = spa_get_random(c);
                mm->mm_root = B_TRUE;

                /*
                 * Check the other, lower-index DVAs to see if they're on
                 * the same vdev as the child we picked.  If they are, use
                 * them since they are likely to have been allocated from
                 * the primary metaslab in use at the time, and hence are
                 * more likely to have locality with single-copy data.
                 */
                for (c = mm->mm_preferred, d = c - 1; d >= 0; d--) {
                        if (DVA_GET_VDEV(&dva[d]) == DVA_GET_VDEV(&dva[c]))
                                mm->mm_preferred = d;
                }

                for (c = 0; c < mm->mm_children; c++) {
                        mc = &mm->mm_child[c];

                        mc->mc_vd = vdev_lookup_top(spa, DVA_GET_VDEV(&dva[c]));
                        mc->mc_offset = DVA_GET_OFFSET(&dva[c]);
                }
        } else {
                int lowest_pending = INT_MAX;
                int lowest_nr = 1;

                c = vd->vdev_children;

                mm = kmem_zalloc(offsetof(mirror_map_t, mm_child[c]),
                    KM_PUSHPAGE);
                mm->mm_children = c;
                mm->mm_replacing = (vd->vdev_ops == &vdev_replacing_ops ||
                    vd->vdev_ops == &vdev_spare_ops);
                mm->mm_preferred = 0;
                mm->mm_root = B_FALSE;

                for (c = 0; c < mm->mm_children; c++) {
                        mc = &mm->mm_child[c];
                        mc->mc_vd = vd->vdev_child[c];
                        mc->mc_offset = zio->io_offset;

                        if (mm->mm_replacing)
                                continue;

                        if (!vdev_readable(mc->mc_vd)) {
                                mc->mc_error = SET_ERROR(ENXIO);
                                mc->mc_tried = 1;
                                mc->mc_skipped = 1;
                                mc->mc_pending = INT_MAX;
                                continue;
                        }

                        mc->mc_pending = vdev_mirror_pending(mc->mc_vd);
                        if (mc->mc_pending < lowest_pending) {
                                lowest_pending = mc->mc_pending;
                                lowest_nr = 1;
                        } else if (mc->mc_pending == lowest_pending) {
                                lowest_nr++;
                        }
                }

                d = gethrtime() / (NSEC_PER_USEC * zfs_vdev_mirror_switch_us);
                d = (d % lowest_nr) + 1;

                for (c = 0; c < mm->mm_children; c++) {
                        mc = &mm->mm_child[c];

                        if (mm->mm_child[c].mc_pending == lowest_pending) {
                                if (--d == 0) {
                                        mm->mm_preferred = c;
                                        break;
                                }
                        }
                }
        }

        zio->io_vsd = mm;
        zio->io_vsd_ops = &vdev_mirror_vsd_ops;
        return (mm);
}

static int
vdev_mirror_open(vdev_t *vd, uint64_t *asize, uint64_t *max_asize,
    uint64_t *ashift)
{
        int numerrors = 0;
        int lasterror = 0;
        int c;

        if (vd->vdev_children == 0) {
                vd->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL;
                return (SET_ERROR(EINVAL));
        }

        vdev_open_children(vd);

        for (c = 0; c < vd->vdev_children; c++) {
                vdev_t *cvd = vd->vdev_child[c];

                if (cvd->vdev_open_error) {
                        lasterror = cvd->vdev_open_error;
                        numerrors++;
                        continue;
                }

                *asize = MIN(*asize - 1, cvd->vdev_asize - 1) + 1;
                *max_asize = MIN(*max_asize - 1, cvd->vdev_max_asize - 1) + 1;
                *ashift = MAX(*ashift, cvd->vdev_ashift);
        }

        if (numerrors == vd->vdev_children) {
                vd->vdev_stat.vs_aux = VDEV_AUX_NO_REPLICAS;
                return (lasterror);
        }

        return (0);
}

static void
vdev_mirror_close(vdev_t *vd)
{
        int c;

        for (c = 0; c < vd->vdev_children; c++)
                vdev_close(vd->vdev_child[c]);
}

static void
vdev_mirror_child_done(zio_t *zio)
{
        mirror_child_t *mc = zio->io_private;

        mc->mc_error = zio->io_error;
        mc->mc_tried = 1;
        mc->mc_skipped = 0;
}

static void
vdev_mirror_scrub_done(zio_t *zio)
{
        mirror_child_t *mc = zio->io_private;

        if (zio->io_error == 0) {
                zio_t *pio;

                mutex_enter(&zio->io_lock);
                while ((pio = zio_walk_parents(zio)) != NULL) {
                        mutex_enter(&pio->io_lock);
                        ASSERT3U(zio->io_size, >=, pio->io_size);
                        bcopy(zio->io_data, pio->io_data, pio->io_size);
                        mutex_exit(&pio->io_lock);
                }
                mutex_exit(&zio->io_lock);
        }

        zio_buf_free(zio->io_data, zio->io_size);

        mc->mc_error = zio->io_error;
        mc->mc_tried = 1;
        mc->mc_skipped = 0;
}

/*
 * Try to find a child whose DTL doesn't contain the block we want to read.
 * If we can't, try the read on any vdev we haven't already tried.
 */
static int
vdev_mirror_child_select(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;
        mirror_child_t *mc;
        uint64_t txg = zio->io_txg;
        int i, c;

        ASSERT(zio->io_bp == NULL || BP_PHYSICAL_BIRTH(zio->io_bp) == txg);

        /*
         * Try to find a child whose DTL doesn't contain the block to read.
         * If a child is known to be completely inaccessible (indicated by
         * vdev_readable() returning B_FALSE), don't even try.
         */
        for (i = 0, c = mm->mm_preferred; i < mm->mm_children; i++, c++) {
                if (c >= mm->mm_children)
                        c = 0;
                mc = &mm->mm_child[c];
                if (mc->mc_tried || mc->mc_skipped)
                        continue;
                if (!vdev_readable(mc->mc_vd)) {
                        mc->mc_error = SET_ERROR(ENXIO);
                        mc->mc_tried = 1;       /* don't even try */
                        mc->mc_skipped = 1;
                        continue;
                }
                if (!vdev_dtl_contains(mc->mc_vd, DTL_MISSING, txg, 1))
                        return (c);
                mc->mc_error = SET_ERROR(ESTALE);
                mc->mc_skipped = 1;
                mc->mc_speculative = 1;
        }

        /*
         * Every device is either missing or has this txg in its DTL.
         * Look for any child we haven't already tried before giving up.
         */
        for (c = 0; c < mm->mm_children; c++)
                if (!mm->mm_child[c].mc_tried)
                        return (c);

        /*
         * Every child failed.  There's no place left to look.
         */
        return (-1);
}

static int
vdev_mirror_io_start(zio_t *zio)
{
        mirror_map_t *mm;
        mirror_child_t *mc;
        int c, children;

        mm = vdev_mirror_map_alloc(zio);

        if (zio->io_type == ZIO_TYPE_READ) {
                if ((zio->io_flags & ZIO_FLAG_SCRUB) && !mm->mm_replacing) {
                        /*
                         * For scrubbing reads we need to allocate a read
                         * buffer for each child and issue reads to all
                         * children.  If any child succeeds, it will copy its
                         * data into zio->io_data in vdev_mirror_scrub_done.
                         */
                        for (c = 0; c < mm->mm_children; c++) {
                                mc = &mm->mm_child[c];
                                zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                                    mc->mc_vd, mc->mc_offset,
                                    zio_buf_alloc(zio->io_size), zio->io_size,
                                    zio->io_type, zio->io_priority, 0,
                                    vdev_mirror_scrub_done, mc));
                        }
                        return (ZIO_PIPELINE_CONTINUE);
                }
                /*
                 * For normal reads just pick one child.
                 */
                c = vdev_mirror_child_select(zio);
                children = (c >= 0);
        } else {
                ASSERT(zio->io_type == ZIO_TYPE_WRITE);

                /*
                 * Writes go to all children.
                 */
                c = 0;
                children = mm->mm_children;
        }

        while (children--) {
                mc = &mm->mm_child[c];
                zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                    mc->mc_vd, mc->mc_offset, zio->io_data, zio->io_size,
                    zio->io_type, zio->io_priority, 0,
                    vdev_mirror_child_done, mc));
                c++;
        }

        return (ZIO_PIPELINE_CONTINUE);
}

static int
vdev_mirror_worst_error(mirror_map_t *mm)
{
        int c, error[2] = { 0, 0 };

        for (c = 0; c < mm->mm_children; c++) {
                mirror_child_t *mc = &mm->mm_child[c];
                int s = mc->mc_speculative;
                error[s] = zio_worst_error(error[s], mc->mc_error);
        }

        return (error[0] ? error[0] : error[1]);
}

static void
vdev_mirror_io_done(zio_t *zio)
{
        mirror_map_t *mm = zio->io_vsd;
        mirror_child_t *mc;
        int c;
        int good_copies = 0;
        int unexpected_errors = 0;

        for (c = 0; c < mm->mm_children; c++) {
                mc = &mm->mm_child[c];

                if (mc->mc_error) {
                        if (!mc->mc_skipped)
                                unexpected_errors++;
                } else if (mc->mc_tried) {
                        good_copies++;
                }
        }

        if (zio->io_type == ZIO_TYPE_WRITE) {
                /*
                 * XXX -- for now, treat partial writes as success.
                 *
                 * Now that we support write reallocation, it would be better
                 * to treat partial failure as real failure unless there are
                 * no non-degraded top-level vdevs left, and not update DTLs
                 * if we intend to reallocate.
                 */
                /* XXPOLICY */
                if (good_copies != mm->mm_children) {
                        /*
                         * Always require at least one good copy.
                         *
                         * For ditto blocks (io_vd == NULL), require
                         * all copies to be good.
                         *
                         * XXX -- for replacing vdevs, there's no great answer.
                         * If the old device is really dead, we may not even
                         * be able to access it -- so we only want to
                         * require good writes to the new device.  But if
                         * the new device turns out to be flaky, we want
                         * to be able to detach it -- which requires all
                         * writes to the old device to have succeeded.
                         */
                        if (good_copies == 0 || zio->io_vd == NULL)
                                zio->io_error = vdev_mirror_worst_error(mm);
                }
                return;
        }

        ASSERT(zio->io_type == ZIO_TYPE_READ);

        /*
         * If we don't have a good copy yet, keep trying other children.
         */
        /* XXPOLICY */
        if (good_copies == 0 && (c = vdev_mirror_child_select(zio)) != -1) {
                ASSERT(c >= 0 && c < mm->mm_children);
                mc = &mm->mm_child[c];
                zio_vdev_io_redone(zio);
                zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                    mc->mc_vd, mc->mc_offset, zio->io_data, zio->io_size,
                    ZIO_TYPE_READ, zio->io_priority, 0,
                    vdev_mirror_child_done, mc));
                return;
        }

        /* XXPOLICY */
        if (good_copies == 0) {
                zio->io_error = vdev_mirror_worst_error(mm);
                ASSERT(zio->io_error != 0);
        }

        if (good_copies && spa_writeable(zio->io_spa) &&
            (unexpected_errors ||
            (zio->io_flags & ZIO_FLAG_RESILVER) ||
            ((zio->io_flags & ZIO_FLAG_SCRUB) && mm->mm_replacing))) {
                /*
                 * Use the good data we have in hand to repair damaged children.
                 */
                for (c = 0; c < mm->mm_children; c++) {
                        /*
                         * Don't rewrite known good children.
                         * Not only is it unnecessary, it could
                         * actually be harmful: if the system lost
                         * power while rewriting the only good copy,
                         * there would be no good copies left!
                         */
                        mc = &mm->mm_child[c];

                        if (mc->mc_error == 0) {
                                if (mc->mc_tried)
                                        continue;
                                if (!(zio->io_flags & ZIO_FLAG_SCRUB) &&
                                    !vdev_dtl_contains(mc->mc_vd, DTL_PARTIAL,
                                    zio->io_txg, 1))
                                        continue;
                                mc->mc_error = SET_ERROR(ESTALE);
                        }

                        zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
                            mc->mc_vd, mc->mc_offset,
                            zio->io_data, zio->io_size,
                            ZIO_TYPE_WRITE, ZIO_PRIORITY_ASYNC_WRITE,
                            ZIO_FLAG_IO_REPAIR | (unexpected_errors ?
                            ZIO_FLAG_SELF_HEAL : 0), NULL, NULL));
                }
        }
}

static void
vdev_mirror_state_change(vdev_t *vd, int faulted, int degraded)
{
        if (faulted == vd->vdev_children)
                vdev_set_state(vd, B_FALSE, VDEV_STATE_CANT_OPEN,
                    VDEV_AUX_NO_REPLICAS);
        else if (degraded + faulted != 0)
                vdev_set_state(vd, B_FALSE, VDEV_STATE_DEGRADED, VDEV_AUX_NONE);
        else
                vdev_set_state(vd, B_FALSE, VDEV_STATE_HEALTHY, VDEV_AUX_NONE);
}

vdev_ops_t vdev_mirror_ops = {
        vdev_mirror_open,
        vdev_mirror_close,
        vdev_default_asize,
        vdev_mirror_io_start,
        vdev_mirror_io_done,
        vdev_mirror_state_change,
        NULL,
        NULL,
        VDEV_TYPE_MIRROR,       /* name of this vdev type */
        B_FALSE                 /* not a leaf vdev */
};

vdev_ops_t vdev_replacing_ops = {
        vdev_mirror_open,
        vdev_mirror_close,
        vdev_default_asize,
        vdev_mirror_io_start,
        vdev_mirror_io_done,
        vdev_mirror_state_change,
        NULL,
        NULL,
        VDEV_TYPE_REPLACING,    /* name of this vdev type */
        B_FALSE                 /* not a leaf vdev */
};

vdev_ops_t vdev_spare_ops = {
        vdev_mirror_open,
        vdev_mirror_close,
        vdev_default_asize,
        vdev_mirror_io_start,
        vdev_mirror_io_done,
        vdev_mirror_state_change,
        NULL,
        NULL,
        VDEV_TYPE_SPARE,        /* name of this vdev type */
        B_FALSE                 /* not a leaf vdev */
};

#if defined(_KERNEL) && defined(HAVE_SPL)
module_param(zfs_vdev_mirror_switch_us, int, 0644);
MODULE_PARM_DESC(zfs_vdev_mirror_switch_us, "Switch mirrors every N usecs");
#endif