cfq-iosched.c

Linux块设备驱动源码

/*
 *  linux/drivers/block/cfq-iosched.c
 *
 *  CFQ, or complete fairness queueing, disk scheduler.
 *
 *  Based on ideas from a previously unfinished io
 *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
 *
 *  Copyright (C) 2003 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>
#include <linux/mempool.h>
#include <linux/ioprio.h>
#include <linux/writeback.h>

/*
 * tunables
 */
static int cfq_quantum = 4;		/* max queue in one round of service */
static int cfq_queued = 8;		/* minimum rq allocate limit per-queue*/
static int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
static int cfq_back_max = 16 * 1024;	/* maximum backwards seek, in KiB */
static int cfq_back_penalty = 2;	/* penalty of a backwards seek */

static int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 100;

#define CFQ_IDLE_GRACE		(HZ / 10)
#define CFQ_SLICE_SCALE		(5)

#define CFQ_KEY_ASYNC		(0)
#define CFQ_KEY_ANY		(0xffff)

/*
 * disable queueing at the driver/hardware level
 */
static int cfq_max_depth = 2;

/*
 * for the hash of cfqq inside the cfqd
 */
#define CFQ_QHASH_SHIFT		6
#define CFQ_QHASH_ENTRIES	(1 << CFQ_QHASH_SHIFT)
#define list_entry_qhash(entry)	hlist_entry((entry), struct cfq_queue, cfq_hash)

/*
 * for the hash of crq inside the cfqq
 */
#define CFQ_MHASH_SHIFT		6
#define CFQ_MHASH_BLOCK(sec)	((sec) >> 3)
#define CFQ_MHASH_ENTRIES	(1 << CFQ_MHASH_SHIFT)
#define CFQ_MHASH_FN(sec)	hash_long(CFQ_MHASH_BLOCK(sec), CFQ_MHASH_SHIFT)
#define rq_hash_key(rq)		((rq)->sector + (rq)->nr_sectors)
#define list_entry_hash(ptr)	hlist_entry((ptr), struct cfq_rq, hash)

#define list_entry_cfqq(ptr)	list_entry((ptr), struct cfq_queue, cfq_list)
#define list_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)

#define RQ_DATA(rq)		(rq)->elevator_private

/*
 * rb-tree defines
 */
#define RB_NONE			(2)
#define RB_EMPTY(node)		((node)->rb_node == NULL)
#define RB_CLEAR_COLOR(node)	(node)->rb_color = RB_NONE
#define RB_CLEAR(node)		do {	\
	(node)->rb_parent = NULL;	\
	RB_CLEAR_COLOR((node));		\
	(node)->rb_right = NULL;	\
	(node)->rb_left = NULL;		\
} while (0)
#define RB_CLEAR_ROOT(root)	((root)->rb_node = NULL)
#define ON_RB(node)		((node)->rb_color != RB_NONE)
#define rb_entry_crq(node)	rb_entry((node), struct cfq_rq, rb_node)
#define rq_rb_key(rq)		(rq)->sector

static kmem_cache_t *crq_pool;
static kmem_cache_t *cfq_pool;
static kmem_cache_t *cfq_ioc_pool;

#define CFQ_PRIO_LISTS		IOPRIO_BE_NR
#define cfq_class_idle(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
#define cfq_class_be(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_BE)
#define cfq_class_rt(cfqq)	((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

#define ASYNC			(0)
#define SYNC			(1)

#define cfq_cfqq_dispatched(cfqq)	\
	((cfqq)->on_dispatch[ASYNC] + (cfqq)->on_dispatch[SYNC])

#define cfq_cfqq_class_sync(cfqq)	((cfqq)->key != CFQ_KEY_ASYNC)

#define cfq_cfqq_sync(cfqq)		\
	(cfq_cfqq_class_sync(cfqq) || (cfqq)->on_dispatch[SYNC])

/*
 * Per block device queue structure
 */
struct cfq_data {
	atomic_t ref;
	request_queue_t *queue;

	/*
	 * rr list of queues with requests and the count of them
	 */
	struct list_head rr_list[CFQ_PRIO_LISTS];
	struct list_head busy_rr;
	struct list_head cur_rr;
	struct list_head idle_rr;
	unsigned int busy_queues;

	/*
	 * non-ordered list of empty cfqq's
	 */
	struct list_head empty_list;

	/*
	 * cfqq lookup hash
	 */
	struct hlist_head *cfq_hash;

	/*
	 * global crq hash for all queues
	 */
	struct hlist_head *crq_hash;

	unsigned int max_queued;

	mempool_t *crq_pool;

	int rq_in_driver;

	/*
	 * schedule slice state info
	 */
	/*
	 * idle window management
	 */
	struct timer_list idle_slice_timer;
	struct work_struct unplug_work;

	struct cfq_queue *active_queue;
	struct cfq_io_context *active_cic;
	int cur_prio, cur_end_prio;
	unsigned int dispatch_slice;

	struct timer_list idle_class_timer;

	sector_t last_sector;
	unsigned long last_end_request;

	unsigned int rq_starved;

	/*
	 * tunables, see top of file
	 */
	unsigned int cfq_quantum;
	unsigned int cfq_queued;
	unsigned int cfq_fifo_expire[2];
	unsigned int cfq_back_penalty;
	unsigned int cfq_back_max;
	unsigned int cfq_slice[2];
	unsigned int cfq_slice_async_rq;
	unsigned int cfq_slice_idle;
	unsigned int cfq_max_depth;
};

/*
 * Per process-grouping structure
 */
struct cfq_queue {
	/* reference count */
	atomic_t ref;
	/* parent cfq_data */
	struct cfq_data *cfqd;
	/* cfqq lookup hash */
	struct hlist_node cfq_hash;
	/* hash key */
	unsigned int key;
	/* on either rr or empty list of cfqd */
	struct list_head cfq_list;
	/* sorted list of pending requests */
	struct rb_root sort_list;
	/* if fifo isn't expired, next request to serve */
	struct cfq_rq *next_crq;
	/* requests queued in sort_list */
	int queued[2];
	/* currently allocated requests */
	int allocated[2];
	/* fifo list of requests in sort_list */
	struct list_head fifo;

	unsigned long slice_start;
	unsigned long slice_end;
	unsigned long slice_left;
	unsigned long service_last;

	/* number of requests that are on the dispatch list */
	int on_dispatch[2];

	/* io prio of this group */
	unsigned short ioprio, org_ioprio;
	unsigned short ioprio_class, org_ioprio_class;

	/* various state flags, see below */
	unsigned int flags;
};

struct cfq_rq {
	struct rb_node rb_node;
	sector_t rb_key;
	struct request *request;
	struct hlist_node hash;

	struct cfq_queue *cfq_queue;
	struct cfq_io_context *io_context;

	unsigned int crq_flags;
};

enum cfqq_state_flags {
	CFQ_CFQQ_FLAG_on_rr = 0,
	CFQ_CFQQ_FLAG_wait_request,
	CFQ_CFQQ_FLAG_must_alloc,
	CFQ_CFQQ_FLAG_must_alloc_slice,
	CFQ_CFQQ_FLAG_must_dispatch,
	CFQ_CFQQ_FLAG_fifo_expire,
	CFQ_CFQQ_FLAG_idle_window,
	CFQ_CFQQ_FLAG_prio_changed,
	CFQ_CFQQ_FLAG_expired,
};

#define CFQ_CFQQ_FNS(name)						\
static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)		\
{									\
	cfqq->flags |= (1 << CFQ_CFQQ_FLAG_##name);			\
}									\
static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)	\
{									\
	cfqq->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);			\
}									\
static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)		\
{									\
	return (cfqq->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;	\
}

CFQ_CFQQ_FNS(on_rr);
CFQ_CFQQ_FNS(wait_request);
CFQ_CFQQ_FNS(must_alloc);
CFQ_CFQQ_FNS(must_alloc_slice);
CFQ_CFQQ_FNS(must_dispatch);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(expired);
#undef CFQ_CFQQ_FNS

enum cfq_rq_state_flags {
	CFQ_CRQ_FLAG_in_flight = 0,
	CFQ_CRQ_FLAG_in_driver,
	CFQ_CRQ_FLAG_is_sync,
	CFQ_CRQ_FLAG_requeued,
};

#define CFQ_CRQ_FNS(name)						\
static inline void cfq_mark_crq_##name(struct cfq_rq *crq)		\
{									\
	crq->crq_flags |= (1 << CFQ_CRQ_FLAG_##name);			\
}									\
static inline void cfq_clear_crq_##name(struct cfq_rq *crq)		\
{									\
	crq->crq_flags &= ~(1 << CFQ_CRQ_FLAG_##name);			\
}									\
static inline int cfq_crq_##name(const struct cfq_rq *crq)		\
{									\
	return (crq->crq_flags & (1 << CFQ_CRQ_FLAG_##name)) != 0;	\
}

CFQ_CRQ_FNS(in_flight);
CFQ_CRQ_FNS(in_driver);
CFQ_CRQ_FNS(is_sync);
CFQ_CRQ_FNS(requeued);
#undef CFQ_CRQ_FNS

static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsigned short);
static void cfq_dispatch_sort(request_queue_t *, struct cfq_rq *);
static void cfq_put_cfqd(struct cfq_data *cfqd);

#define process_sync(tsk)	((tsk)->flags & PF_SYNCWRITE)

/*
 * lots of deadline iosched dupes, can be abstracted later...
 */
static inline void cfq_del_crq_hash(struct cfq_rq *crq)
{
	hlist_del_init(&crq->hash);
}

static void cfq_remove_merge_hints(request_queue_t *q, struct cfq_rq *crq)
{
	cfq_del_crq_hash(crq);

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

static inline void cfq_add_crq_hash(struct cfq_data *cfqd, struct cfq_rq *crq)
{
	const int hash_idx = CFQ_MHASH_FN(rq_hash_key(crq->request));

	hlist_add_head(&crq->hash, &cfqd->crq_hash[hash_idx]);
}

static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
{
	struct hlist_head *hash_list = &cfqd->crq_hash[CFQ_MHASH_FN(offset)];
	struct hlist_node *entry, *next;

	hlist_for_each_safe(entry, next, hash_list) {
		struct cfq_rq *crq = list_entry_hash(entry);
		struct request *__rq = crq->request;

		if (!rq_mergeable(__rq)) {
			cfq_del_crq_hash(crq);
			continue;
		}

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

	return NULL;
}

static inline int cfq_pending_requests(struct cfq_data *cfqd)
{
	return !list_empty(&cfqd->queue->queue_head) || cfqd->busy_queues;
}

/*
 * scheduler run of queue, if there are requests pending and no one in the
 * driver that will restart queueing
 */
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
	if (!cfqd->rq_in_driver && cfq_pending_requests(cfqd))
		kblockd_schedule_work(&cfqd->unplug_work);
}

static int cfq_queue_empty(request_queue_t *q)
{
	struct cfq_data *cfqd = q->elevator->elevator_data;

	return !cfq_pending_requests(cfqd);
}

/*
 * Lifted from AS - choose which of crq1 and crq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head are penalized and only allowed to a certain extent.
 */
static struct cfq_rq *
cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2)
{
	sector_t last, s1, s2, d1 = 0, d2 = 0;
	int r1_wrap = 0, r2_wrap = 0;	/* requests are behind the disk head */
	unsigned long back_max;

	if (crq1 == NULL || crq1 == crq2)
		return crq2;
	if (crq2 == NULL)
		return crq1;

	if (cfq_crq_requeued(crq1) && !cfq_crq_requeued(crq2))
		return crq1;
	else if (cfq_crq_requeued(crq2) && !cfq_crq_requeued(crq1))
		return crq2;

	if (cfq_crq_is_sync(crq1) && !cfq_crq_is_sync(crq2))
		return crq1;
	else if (cfq_crq_is_sync(crq2) && !cfq_crq_is_sync(crq1))
		return crq2;

	s1 = crq1->request->sector;
	s2 = crq2->request->sector;

	last = cfqd->last_sector;

	/*
	 * by definition, 1KiB is 2 sectors
	 */
	back_max = cfqd->cfq_back_max * 2;

	/*
	 * Strict one way elevator _except_ in the case where we allow
	 * short backward seeks which are biased as twice the cost of a
	 * similar forward seek.
	 */
	if (s1 >= last)
		d1 = s1 - last;
	else if (s1 + back_max >= last)
		d1 = (last - s1) * cfqd->cfq_back_penalty;
	else
		r1_wrap = 1;

	if (s2 >= last)
		d2 = s2 - last;
	else if (s2 + back_max >= last)
		d2 = (last - s2) * cfqd->cfq_back_penalty;
	else
		r2_wrap = 1;

	/* Found required data */
	if (!r1_wrap && r2_wrap)
		return crq1;
	else if (!r2_wrap && r1_wrap)
		return crq2;
	else if (r1_wrap && r2_wrap) {
		/* both behind the head */
		if (s1 <= s2)
			return crq1;
		else
			return crq2;
	}

	/* Both requests in front of the head */
	if (d1 < d2)
		return crq1;
	else if (d2 < d1)
		return crq2;
	else {
		if (s1 >= s2)
			return crq1;
		else
			return crq2;
	}
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct cfq_rq *
cfq_find_next_crq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
		  struct cfq_rq *last)
{
	struct cfq_rq *crq_next = NULL, *crq_prev = NULL;
	struct rb_node *rbnext, *rbprev;

	rbnext = NULL;
	if (ON_RB(&last->rb_node))
		rbnext = rb_next(&last->rb_node);
	if (!rbnext) {
		rbnext = rb_first(&cfqq->sort_list);
		if (rbnext == &last->rb_node)
			rbnext = NULL;
	}

	rbprev = rb_prev(&last->rb_node);

	if (rbprev)
		crq_prev = rb_entry_crq(rbprev);
	if (rbnext)
		crq_next = rb_entry_crq(rbnext);

	return cfq_choose_req(cfqd, crq_next, crq_prev);
}

static void cfq_update_next_crq(struct cfq_rq *crq)
{
	struct cfq_queue *cfqq = crq->cfq_queue;

	if (cfqq->next_crq == crq)
		cfqq->next_crq = cfq_find_next_crq(cfqq->cfqd, cfqq, crq);
}

static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
{
	struct cfq_data *cfqd = cfqq->cfqd;
	struct list_head *list, *entry;

	BUG_ON(!cfq_cfqq_on_rr(cfqq));

	list_del(&cfqq->cfq_list);

	if (cfq_class_rt(cfqq))
		list = &cfqd->cur_rr;
	else if (cfq_class_idle(cfqq))
		list = &cfqd->idle_rr;
	else {
		/*
		 * if cfqq has requests in flight, don't allow it to be
		 * found in cfq_set_active_queue before it has finished them.
		 * this is done to increase fairness between a process that
		 * has lots of io pending vs one that only generates one
		 * sporadically or synchronously
		 */
		if (cfq_cfqq_dispatched(cfqq))
			list = &cfqd->busy_rr;
		else
			list = &cfqd->rr_list[cfqq->ioprio];
	}

	/*
	 * if queue was preempted, just add to front to be fair. busy_rr
	 * isn't sorted.
	 */
	if (preempted || list == &cfqd->busy_rr) {
		list_add(&cfqq->cfq_list, list);
		return;
	}

	/*
	 * sort by when queue was last serviced
	 */
	entry = list;
	while ((entry = entry->prev) != list) {