/*

 * 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.

 */

/*

 * 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)

{

	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);

}

/*

 * 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);

		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);

}