deadline-iosched.c

Linux Kernel 2.6.9 for OMAP1710

/*
 *  linux/drivers/block/deadline-iosched.c
 *
 *  Deadline i/o scheduler.
 *
 *  Copyright (C) 2002 Jens Axboe <[e-mail]>
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/hash.h>
#include <linux/rbtree.h>

/*
 * See Documentation/deadline-iosched.txt
 */
static int read_expire = HZ / 2;  /* max time before a read is submitted. */
static int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
static int writes_starved = 2;    /* max times reads can starve a write */
static int fifo_batch = 16;       /* # of sequential requests treated as one
				     by the above parameters. For throughput. */

static const int deadline_hash_shift = 5;
#define DL_HASH_BLOCK(sec)	((sec) >> 3)
#define DL_HASH_FN(sec)		(hash_long(DL_HASH_BLOCK((sec)), deadline_hash_shift))
#define DL_HASH_ENTRIES		(1 << deadline_hash_shift)
#define rq_hash_key(rq)		((rq)->sector + (rq)->nr_sectors)
#define list_entry_hash(ptr)	list_entry((ptr), struct deadline_rq, hash)
#define ON_HASH(drq)		(drq)->on_hash

struct deadline_data {
	/*
	 * run time data
	 */

	/*
	 * requests (deadline_rq s) are present on both sort_list and fifo_list
	 */
	struct rb_root sort_list[2];	
	struct list_head fifo_list[2];
	
	/*
	 * next in sort order. read, write or both are NULL
	 */
	struct deadline_rq *next_drq[2];
	struct list_head *dispatch;	/* driver dispatch queue */
	struct list_head *hash;		/* request hash */
	unsigned int batching;		/* number of sequential requests made */
	sector_t last_sector;		/* head position */
	unsigned int starved;		/* times reads have starved writes */

	/*
	 * settings that change how the i/o scheduler behaves
	 */
	int fifo_expire[2];
	int fifo_batch;
	int writes_starved;
	int front_merges;

	mempool_t *drq_pool;
};

/*
 * pre-request data.
 */
struct deadline_rq {
	/*
	 * rbtree index, key is the starting offset
	 */
	struct rb_node rb_node;
	sector_t rb_key;

	struct request *request;

	/*
	 * request hash, key is the ending offset (for back merge lookup)
	 */
	struct list_head hash;
	char on_hash;

	/*
	 * expire fifo
	 */
	struct list_head fifo;
	unsigned long expires;
};

static void deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq);

static kmem_cache_t *drq_pool;

#define RQ_DATA(rq)	((struct deadline_rq *) (rq)->elevator_private)

/*
 * the back merge hash support functions
 */
static inline void __deadline_del_drq_hash(struct deadline_rq *drq)
{
	drq->on_hash = 0;
	list_del_init(&drq->hash);
}

static inline void deadline_del_drq_hash(struct deadline_rq *drq)
{
	if (ON_HASH(drq))
		__deadline_del_drq_hash(drq);
}

static void
deadline_remove_merge_hints(request_queue_t *q, struct deadline_rq *drq)
{
	deadline_del_drq_hash(drq);

	if (q->last_merge == drq->request)
		q->last_merge = NULL;
}

static inline void
deadline_add_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
{
	struct request *rq = drq->request;

	BUG_ON(ON_HASH(drq));

	drq->on_hash = 1;
	list_add(&drq->hash, &dd->hash[DL_HASH_FN(rq_hash_key(rq))]);
}

/*
 * move hot entry to front of chain
 */
static inline void
deadline_hot_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
{
	struct request *rq = drq->request;
	struct list_head *head = &dd->hash[DL_HASH_FN(rq_hash_key(rq))];

	if (ON_HASH(drq) && drq->hash.prev != head) {
		list_del(&drq->hash);
		list_add(&drq->hash, head);
	}
}

static struct request *
deadline_find_drq_hash(struct deadline_data *dd, sector_t offset)
{
	struct list_head *hash_list = &dd->hash[DL_HASH_FN(offset)];
	struct list_head *entry, *next = hash_list->next;

	while ((entry = next) != hash_list) {
		struct deadline_rq *drq = list_entry_hash(entry);
		struct request *__rq = drq->request;

		next = entry->next;
		
		BUG_ON(!ON_HASH(drq));

		if (!rq_mergeable(__rq)) {
			__deadline_del_drq_hash(drq);
			continue;
		}

		if (rq_hash_key(__rq) == offset)
			return __rq;
	}

	return NULL;
}

/*
 * rb tree support functions
 */
#define RB_NONE		(2)
#define RB_EMPTY(root)	((root)->rb_node == NULL)
#define ON_RB(node)	((node)->rb_color != RB_NONE)
#define RB_CLEAR(node)	((node)->rb_color = RB_NONE)
#define rb_entry_drq(node)	rb_entry((node), struct deadline_rq, rb_node)
#define DRQ_RB_ROOT(dd, drq)	(&(dd)->sort_list[rq_data_dir((drq)->request)])
#define rq_rb_key(rq)		(rq)->sector

static struct deadline_rq *
__deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
	struct rb_node **p = &DRQ_RB_ROOT(dd, drq)->rb_node;
	struct rb_node *parent = NULL;
	struct deadline_rq *__drq;

	while (*p) {
		parent = *p;
		__drq = rb_entry_drq(parent);

		if (drq->rb_key < __drq->rb_key)
			p = &(*p)->rb_left;
		else if (drq->rb_key > __drq->rb_key)
			p = &(*p)->rb_right;
		else
			return __drq;
	}

	rb_link_node(&drq->rb_node, parent, p);
	return NULL;
}

static void
deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
	struct deadline_rq *__alias;

	drq->rb_key = rq_rb_key(drq->request);

retry:
	__alias = __deadline_add_drq_rb(dd, drq);
	if (!__alias) {
		rb_insert_color(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
		return;
	}

	deadline_move_request(dd, __alias);
	goto retry;
}

static inline void
deadline_del_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
	const int data_dir = rq_data_dir(drq->request);

	if (dd->next_drq[data_dir] == drq) {
		struct rb_node *rbnext = rb_next(&drq->rb_node);

		dd->next_drq[data_dir] = NULL;
		if (rbnext)
			dd->next_drq[data_dir] = rb_entry_drq(rbnext);
	}

	if (ON_RB(&drq->rb_node)) {
		rb_erase(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
		RB_CLEAR(&drq->rb_node);
	}
}

static struct request *
deadline_find_drq_rb(struct deadline_data *dd, sector_t sector, int data_dir)
{
	struct rb_node *n = dd->sort_list[data_dir].rb_node;
	struct deadline_rq *drq;

	while (n) {
		drq = rb_entry_drq(n);

		if (sector < drq->rb_key)
			n = n->rb_left;
		else if (sector > drq->rb_key)
			n = n->rb_right;
		else
			return drq->request;
	}

	return NULL;
}

/*
 * deadline_find_first_drq finds the first (lowest sector numbered) request
 * for the specified data_dir. Used to sweep back to the start of the disk
 * (1-way elevator) after we process the last (highest sector) request.
 */
static struct deadline_rq *
deadline_find_first_drq(struct deadline_data *dd, int data_dir)
{
	struct rb_node *n = dd->sort_list[data_dir].rb_node;

	for (;;) {
		if (n->rb_left == NULL)
			return rb_entry_drq(n);
		
		n = n->rb_left;
	}
}

/*
 * add drq to rbtree and fifo
 */
static inline void
deadline_add_request(struct request_queue *q, struct request *rq)
{
	struct deadline_data *dd = q->elevator.elevator_data;
	struct deadline_rq *drq = RQ_DATA(rq);

	const int data_dir = rq_data_dir(drq->request);

	deadline_add_drq_rb(dd, drq);
	/*
	 * set expire time (only used for reads) and add to fifo list
	 */
	drq->expires = jiffies + dd->fifo_expire[data_dir];
	list_add_tail(&drq->fifo, &dd->fifo_list[data_dir]);

	if (rq_mergeable(rq)) {
		deadline_add_drq_hash(dd, drq);

		if (!q->last_merge)
			q->last_merge = rq;
	}
}

/*
 * remove rq from rbtree, fifo, and hash
 */
static void deadline_remove_request(request_queue_t *q, struct request *rq)
{
	struct deadline_rq *drq = RQ_DATA(rq);

	if (drq) {
		struct deadline_data *dd = q->elevator.elevator_data;

		list_del_init(&drq->fifo);
		deadline_remove_merge_hints(q, drq);
		deadline_del_drq_rb(dd, drq);
	}
}

static int
deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
	struct deadline_data *dd = q->elevator.elevator_data;
	struct request *__rq;
	int ret;

	/*
	 * try last_merge to avoid going to hash
	 */
	ret = elv_try_last_merge(q, bio);
	if (ret != ELEVATOR_NO_MERGE) {
		__rq = q->last_merge;
		goto out_insert;
	}

	/*
	 * see if the merge hash can satisfy a back merge
	 */
	__rq = deadline_find_drq_hash(dd, bio->bi_sector);
	if (__rq) {
		BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);

		if (elv_rq_merge_ok(__rq, bio)) {
			ret = ELEVATOR_BACK_MERGE;
			goto out;
		}
	}

	/*
	 * check for front merge
	 */
	if (dd->front_merges) {
		sector_t rb_key = bio->bi_sector + bio_sectors(bio);

		__rq = deadline_find_drq_rb(dd, rb_key, bio_data_dir(bio));
		if (__rq) {
			BUG_ON(rb_key != rq_rb_key(__rq));

			if (elv_rq_merge_ok(__rq, bio)) {
				ret = ELEVATOR_FRONT_MERGE;
				goto out;
			}
		}
	}

	return ELEVATOR_NO_MERGE;
out:
	q->last_merge = __rq;
out_insert:
	if (ret)
		deadline_hot_drq_hash(dd, RQ_DATA(__rq));
	*req = __rq;
	return ret;
}

static void deadline_merged_request(request_queue_t *q, struct request *req)
{
	struct deadline_data *dd = q->elevator.elevator_data;
	struct deadline_rq *drq = RQ_DATA(req);

	/*
	 * hash always needs to be repositioned, key is end sector
	 */
	deadline_del_drq_hash(drq);
	deadline_add_drq_hash(dd, drq);

	/*
	 * if the merge was a front merge, we need to reposition request
	 */
	if (rq_rb_key(req) != drq->rb_key) {
		deadline_del_drq_rb(dd, drq);
		deadline_add_drq_rb(dd, drq);
	}

	q->last_merge = req;
}

static void
deadline_merged_requests(request_queue_t *q, struct request *req,
			 struct request *next)
{
	struct deadline_data *dd = q->elevator.elevator_data;
	struct deadline_rq *drq = RQ_DATA(req);
	struct deadline_rq *dnext = RQ_DATA(next);

	BUG_ON(!drq);
	BUG_ON(!dnext);

	/*
	 * reposition drq (this is the merged request) in hash, and in rbtree
	 * in case of a front merge
	 */
	deadline_del_drq_hash(drq);
	deadline_add_drq_hash(dd, drq);

	if (rq_rb_key(req) != drq->rb_key) {
		deadline_del_drq_rb(dd, drq);
		deadline_add_drq_rb(dd, drq);
	}

	/*
	 * if dnext expires before drq, assign its expire time to drq
	 * and move into dnext position (dnext will be deleted) in fifo
	 */
	if (!list_empty(&drq->fifo) && !list_empty(&dnext->fifo)) {
		if (time_before(dnext->expires, drq->expires)) {
			list_move(&drq->fifo, &dnext->fifo);
			drq->expires = dnext->expires;
		}
	}

	/*
	 * kill knowledge of next, this one is a goner
	 */
	deadline_remove_request(q, next);
}

/*
 * move request from sort list to dispatch queue.
 */
static inline void
deadline_move_to_dispatch(struct deadline_data *dd, struct deadline_rq *drq)
{
	request_queue_t *q = drq->request->q;

	deadline_remove_request(q, drq->request);
	list_add_tail(&drq->request->queuelist, dd->dispatch);
}

/*
 * move an entry to dispatch queue
 */
static void
deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq)
{
	const int data_dir = rq_data_dir(drq->request);
	struct rb_node *rbnext = rb_next(&drq->rb_node);

	dd->next_drq[READ] = NULL;
	dd->next_drq[WRITE] = NULL;

	if (rbnext)
		dd->next_drq[data_dir] = rb_entry_drq(rbnext);