cfq-iosched: enable idling for last queue on priority class

[safe/jmp/linux-2.6] / 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 <axboe@kernel.dk>
 */
#include <linux/module.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/rbtree.h>
#include <linux/ioprio.h>
#include <linux/blktrace_api.h>

/*
 * tunables
 */
/* max queue in one round of service */
static const int cfq_quantum = 4;
static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
/* maximum backwards seek, in KiB */
static const int cfq_back_max = 16 * 1024;
/* penalty of a backwards seek */
static const int cfq_back_penalty = 2;
static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 125;
static const int cfq_target_latency = HZ * 3/10; /* 300 ms */
static const int cfq_hist_divisor = 4;

/*
 * offset from end of service tree
 */
#define CFQ_IDLE_DELAY          (HZ / 5)

/*
 * below this threshold, we consider thinktime immediate
 */
#define CFQ_MIN_TT              (2)

/*
 * Allow merged cfqqs to perform this amount of seeky I/O before
 * deciding to break the queues up again.
 */
#define CFQQ_COOP_TOUT          (HZ)

#define CFQ_SLICE_SCALE         (5)
#define CFQ_HW_QUEUE_MIN        (5)

#define RQ_CIC(rq)              \
        ((struct cfq_io_context *) (rq)->elevator_private)
#define RQ_CFQQ(rq)             (struct cfq_queue *) ((rq)->elevator_private2)

static struct kmem_cache *cfq_pool;
static struct kmem_cache *cfq_ioc_pool;

static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);
static struct completion *ioc_gone;
static DEFINE_SPINLOCK(ioc_gone_lock);

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

#define sample_valid(samples)   ((samples) > 80)

/*
 * Most of our rbtree usage is for sorting with min extraction, so
 * if we cache the leftmost node we don't have to walk down the tree
 * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
 * move this into the elevator for the rq sorting as well.
 */
struct cfq_rb_root {
        struct rb_root rb;
        struct rb_node *left;
        unsigned count;
};
#define CFQ_RB_ROOT     (struct cfq_rb_root) { RB_ROOT, NULL, 0, }

/*
 * Per process-grouping structure
 */
struct cfq_queue {
        /* reference count */
        atomic_t ref;
        /* various state flags, see below */
        unsigned int flags;
        /* parent cfq_data */
        struct cfq_data *cfqd;
        /* service_tree member */
        struct rb_node rb_node;
        /* service_tree key */
        unsigned long rb_key;
        /* prio tree member */
        struct rb_node p_node;
        /* prio tree root we belong to, if any */
        struct rb_root *p_root;
        /* sorted list of pending requests */
        struct rb_root sort_list;
        /* if fifo isn't expired, next request to serve */
        struct request *next_rq;
        /* 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_end;
        long slice_resid;
        unsigned int slice_dispatch;

        /* pending metadata requests */
        int meta_pending;
        /* number of requests that are on the dispatch list or inside driver */
        int dispatched;

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

        unsigned int seek_samples;
        u64 seek_total;
        sector_t seek_mean;
        sector_t last_request_pos;
        unsigned long seeky_start;

        pid_t pid;

        struct cfq_rb_root *service_tree;
        struct cfq_queue *new_cfqq;
};

/*
 * Index in the service_trees.
 * IDLE is handled separately, so it has negative index
 */
enum wl_prio_t {
        IDLE_WORKLOAD = -1,
        BE_WORKLOAD = 0,
        RT_WORKLOAD = 1
};

/*
 * Per block device queue structure
 */
struct cfq_data {
        struct request_queue *queue;

        /*
         * rr lists of queues with requests, onle rr for each priority class.
         * Counts are embedded in the cfq_rb_root
         */
        struct cfq_rb_root service_trees[2];
        struct cfq_rb_root service_tree_idle;
        /*
         * The priority currently being served
         */
        enum wl_prio_t serving_prio;

        /*
         * Each priority tree is sorted by next_request position.  These
         * trees are used when determining if two or more queues are
         * interleaving requests (see cfq_close_cooperator).
         */
        struct rb_root prio_trees[CFQ_PRIO_LISTS];

        unsigned int busy_queues;
        unsigned int busy_queues_avg[2];

        int rq_in_driver[2];
        int sync_flight;

        /*
         * queue-depth detection
         */
        int rq_queued;
        int hw_tag;
        int hw_tag_samples;
        int rq_in_driver_peak;

        /*
         * 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;

        /*
         * async queue for each priority case
         */
        struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
        struct cfq_queue *async_idle_cfqq;

        sector_t last_position;

        /*
         * tunables, see top of file
         */
        unsigned int cfq_quantum;
        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_latency;

        struct list_head cic_list;

        /*
         * Fallback dummy cfqq for extreme OOM conditions
         */
        struct cfq_queue oom_cfqq;

        unsigned long last_end_sync_rq;
};

static struct cfq_rb_root *service_tree_for(enum wl_prio_t prio,
                                            struct cfq_data *cfqd)
{
        if (prio == IDLE_WORKLOAD)
                return &cfqd->service_tree_idle;

        return &cfqd->service_trees[prio];
}

enum cfqq_state_flags {
        CFQ_CFQQ_FLAG_on_rr = 0,        /* on round-robin busy list */
        CFQ_CFQQ_FLAG_wait_request,     /* waiting for a request */
        CFQ_CFQQ_FLAG_must_dispatch,    /* must be allowed a dispatch */
        CFQ_CFQQ_FLAG_must_alloc_slice, /* per-slice must_alloc flag */
        CFQ_CFQQ_FLAG_fifo_expire,      /* FIFO checked in this slice */
        CFQ_CFQQ_FLAG_idle_window,      /* slice idling enabled */
        CFQ_CFQQ_FLAG_prio_changed,     /* task priority has changed */
        CFQ_CFQQ_FLAG_slice_new,        /* no requests dispatched in slice */
        CFQ_CFQQ_FLAG_sync,             /* synchronous queue */
        CFQ_CFQQ_FLAG_coop,             /* cfqq is shared */
};

#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_dispatch);
CFQ_CFQQ_FNS(must_alloc_slice);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(slice_new);
CFQ_CFQQ_FNS(sync);
CFQ_CFQQ_FNS(coop);
#undef CFQ_CFQQ_FNS

#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
        blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
#define cfq_log(cfqd, fmt, args...)     \
        blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)

static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
{
        if (cfq_class_idle(cfqq))
                return IDLE_WORKLOAD;
        if (cfq_class_rt(cfqq))
                return RT_WORKLOAD;
        return BE_WORKLOAD;
}

static inline int cfq_busy_queues_wl(enum wl_prio_t wl, struct cfq_data *cfqd)
{
        if (wl == IDLE_WORKLOAD)
                return cfqd->service_tree_idle.count;

        return cfqd->service_trees[wl].count;
}

static void cfq_dispatch_insert(struct request_queue *, struct request *);
static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
                                       struct io_context *, gfp_t);
static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
                                                struct io_context *);

static inline int rq_in_driver(struct cfq_data *cfqd)
{
        return cfqd->rq_in_driver[0] + cfqd->rq_in_driver[1];
}

static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
                                            bool is_sync)
{
        return cic->cfqq[is_sync];
}

static inline void cic_set_cfqq(struct cfq_io_context *cic,
                                struct cfq_queue *cfqq, bool is_sync)
{
        cic->cfqq[is_sync] = cfqq;
}

/*
 * We regard a request as SYNC, if it's either a read or has the SYNC bit
 * set (in which case it could also be direct WRITE).
 */
static inline bool cfq_bio_sync(struct bio *bio)
{
        return bio_data_dir(bio) == READ || bio_rw_flagged(bio, BIO_RW_SYNCIO);
}

/*
 * 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->busy_queues) {
                cfq_log(cfqd, "schedule dispatch");
                kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
        }
}

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

        return !cfqd->busy_queues;
}

/*
 * Scale schedule slice based on io priority. Use the sync time slice only
 * if a queue is marked sync and has sync io queued. A sync queue with async
 * io only, should not get full sync slice length.
 */
static inline int cfq_prio_slice(struct cfq_data *cfqd, bool sync,
                                 unsigned short prio)
{
        const int base_slice = cfqd->cfq_slice[sync];

        WARN_ON(prio >= IOPRIO_BE_NR);

        return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
}

static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
}

/*
 * get averaged number of queues of RT/BE priority.
 * average is updated, with a formula that gives more weight to higher numbers,
 * to quickly follows sudden increases and decrease slowly
 */

static inline unsigned
cfq_get_avg_queues(struct cfq_data *cfqd, bool rt) {
        unsigned min_q, max_q;
        unsigned mult  = cfq_hist_divisor - 1;
        unsigned round = cfq_hist_divisor / 2;
        unsigned busy = cfq_busy_queues_wl(rt, cfqd);

        min_q = min(cfqd->busy_queues_avg[rt], busy);
        max_q = max(cfqd->busy_queues_avg[rt], busy);
        cfqd->busy_queues_avg[rt] = (mult * max_q + min_q + round) /
                cfq_hist_divisor;
        return cfqd->busy_queues_avg[rt];
}

static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
        if (cfqd->cfq_latency) {
                /* interested queues (we consider only the ones with the same
                 * priority class) */
                unsigned iq = cfq_get_avg_queues(cfqd, cfq_class_rt(cfqq));
                unsigned sync_slice = cfqd->cfq_slice[1];
                unsigned expect_latency = sync_slice * iq;
                if (expect_latency > cfq_target_latency) {
                        unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
                        /* scale low_slice according to IO priority
                         * and sync vs async */
                        unsigned low_slice =
                                min(slice, base_low_slice * slice / sync_slice);
                        /* the adapted slice value is scaled to fit all iqs
                         * into the target latency */
                        slice = max(slice * cfq_target_latency / expect_latency,
                                    low_slice);
                }
        }
        cfqq->slice_end = jiffies + slice;
        cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
}

/*
 * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
 * isn't valid until the first request from the dispatch is activated
 * and the slice time set.
 */
static inline bool cfq_slice_used(struct cfq_queue *cfqq)
{
        if (cfq_cfqq_slice_new(cfqq))
                return 0;
        if (time_before(jiffies, cfqq->slice_end))
                return 0;

        return 1;
}

/*
 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head is penalized and only allowed to a certain extent.
 */
static struct request *
cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)
{
        sector_t last, s1, s2, d1 = 0, d2 = 0;
        unsigned long back_max;
#define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
#define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
        unsigned wrap = 0; /* bit mask: requests behind the disk head? */

        if (rq1 == NULL || rq1 == rq2)
                return rq2;
        if (rq2 == NULL)
                return rq1;

        if (rq_is_sync(rq1) && !rq_is_sync(rq2))
                return rq1;
        else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
                return rq2;
        if (rq_is_meta(rq1) && !rq_is_meta(rq2))
                return rq1;
        else if (rq_is_meta(rq2) && !rq_is_meta(rq1))
                return rq2;

        s1 = blk_rq_pos(rq1);
        s2 = blk_rq_pos(rq2);

        last = cfqd->last_position;

        /*
         * 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
                wrap |= CFQ_RQ1_WRAP;

        if (s2 >= last)
                d2 = s2 - last;
        else if (s2 + back_max >= last)
                d2 = (last - s2) * cfqd->cfq_back_penalty;
        else
                wrap |= CFQ_RQ2_WRAP;

        /* Found required data */

        /*
         * By doing switch() on the bit mask "wrap" we avoid having to
         * check two variables for all permutations: --> faster!
         */
        switch (wrap) {
        case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
                if (d1 < d2)
                        return rq1;
                else if (d2 < d1)
                        return rq2;
                else {
                        if (s1 >= s2)
                                return rq1;
                        else
                                return rq2;
                }

        case CFQ_RQ2_WRAP:
                return rq1;
        case CFQ_RQ1_WRAP:
                return rq2;
        case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
        default:
                /*
                 * Since both rqs are wrapped,
                 * start with the one that's further behind head
                 * (--> only *one* back seek required),
                 * since back seek takes more time than forward.
                 */
                if (s1 <= s2)
                        return rq1;
                else
                        return rq2;
        }
}

/*
 * The below is leftmost cache rbtree addon
 */
static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
{
        if (!root->left)
                root->left = rb_first(&root->rb);

        if (root->left)
                return rb_entry(root->left, struct cfq_queue, rb_node);

        return NULL;
}

static void rb_erase_init(struct rb_node *n, struct rb_root *root)
{
        rb_erase(n, root);
        RB_CLEAR_NODE(n);
}

static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
{
        if (root->left == n)
                root->left = NULL;
        rb_erase_init(n, &root->rb);
        --root->count;
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct request *
cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                  struct request *last)
{
        struct rb_node *rbnext = rb_next(&last->rb_node);
        struct rb_node *rbprev = rb_prev(&last->rb_node);
        struct request *next = NULL, *prev = NULL;

        BUG_ON(RB_EMPTY_NODE(&last->rb_node));

        if (rbprev)
                prev = rb_entry_rq(rbprev);

        if (rbnext)
                next = rb_entry_rq(rbnext);
        else {
                rbnext = rb_first(&cfqq->sort_list);
                if (rbnext && rbnext != &last->rb_node)
                        next = rb_entry_rq(rbnext);
        }

        return cfq_choose_req(cfqd, next, prev);
}

static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
                                      struct cfq_queue *cfqq)
{
        /*
         * just an approximation, should be ok.
         */
        return (cfqd->busy_queues - 1) * (cfq_prio_slice(cfqd, 1, 0) -
                       cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
}

/*
 * The cfqd->service_trees holds all pending cfq_queue's that have
 * requests waiting to be processed. It is sorted in the order that
 * we will service the queues.
 */
static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                                 bool add_front)
{
        struct rb_node **p, *parent;
        struct cfq_queue *__cfqq;
        unsigned long rb_key;
        struct cfq_rb_root *service_tree;
        int left;

        service_tree = service_tree_for(cfqq_prio(cfqq), cfqd);
        if (cfq_class_idle(cfqq)) {
                rb_key = CFQ_IDLE_DELAY;
                parent = rb_last(&service_tree->rb);
                if (parent && parent != &cfqq->rb_node) {
                        __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
                        rb_key += __cfqq->rb_key;
                } else
                        rb_key += jiffies;
        } else if (!add_front) {
                /*
                 * Get our rb key offset. Subtract any residual slice
                 * value carried from last service. A negative resid
                 * count indicates slice overrun, and this should position
                 * the next service time further away in the tree.
                 */
                rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
                rb_key -= cfqq->slice_resid;
                cfqq->slice_resid = 0;
        } else {
                rb_key = -HZ;
                __cfqq = cfq_rb_first(service_tree);
                rb_key += __cfqq ? __cfqq->rb_key : jiffies;
        }

        if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
                /*
                 * same position, nothing more to do
                 */
                if (rb_key == cfqq->rb_key &&
                    cfqq->service_tree == service_tree)
                        return;

                cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
                cfqq->service_tree = NULL;
        }

        left = 1;
        parent = NULL;
        cfqq->service_tree = service_tree;
        p = &service_tree->rb.rb_node;
        while (*p) {
                struct rb_node **n;

                parent = *p;
                __cfqq = rb_entry(parent, struct cfq_queue, rb_node);

                /*
                 * sort by key, that represents service time.
                 */
                if (time_before(rb_key, __cfqq->rb_key))
                        n = &(*p)->rb_left;
                else {
                        n = &(*p)->rb_right;
                        left = 0;
                }

                p = n;
        }

        if (left)
                service_tree->left = &cfqq->rb_node;

        cfqq->rb_key = rb_key;
        rb_link_node(&cfqq->rb_node, parent, p);
        rb_insert_color(&cfqq->rb_node, &service_tree->rb);
        service_tree->count++;
}

static struct cfq_queue *
cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
                     sector_t sector, struct rb_node **ret_parent,
                     struct rb_node ***rb_link)
{
        struct rb_node **p, *parent;
        struct cfq_queue *cfqq = NULL;

        parent = NULL;
        p = &root->rb_node;
        while (*p) {
                struct rb_node **n;

                parent = *p;
                cfqq = rb_entry(parent, struct cfq_queue, p_node);

                /*
                 * Sort strictly based on sector.  Smallest to the left,
                 * largest to the right.
                 */
                if (sector > blk_rq_pos(cfqq->next_rq))
                        n = &(*p)->rb_right;
                else if (sector < blk_rq_pos(cfqq->next_rq))
                        n = &(*p)->rb_left;
                else
                        break;
                p = n;
                cfqq = NULL;
        }

        *ret_parent = parent;
        if (rb_link)
                *rb_link = p;
        return cfqq;
}

static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        struct rb_node **p, *parent;
        struct cfq_queue *__cfqq;

        if (cfqq->p_root) {
                rb_erase(&cfqq->p_node, cfqq->p_root);
                cfqq->p_root = NULL;
        }

        if (cfq_class_idle(cfqq))
                return;
        if (!cfqq->next_rq)
                return;

        cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
        __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
                                      blk_rq_pos(cfqq->next_rq), &parent, &p);
        if (!__cfqq) {
                rb_link_node(&cfqq->p_node, parent, p);
                rb_insert_color(&cfqq->p_node, cfqq->p_root);
        } else
                cfqq->p_root = NULL;
}

/*
 * Update cfqq's position in the service tree.
 */
static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        /*
         * Resorting requires the cfqq to be on the RR list already.
         */
        if (cfq_cfqq_on_rr(cfqq)) {
                cfq_service_tree_add(cfqd, cfqq, 0);
                cfq_prio_tree_add(cfqd, cfqq);
        }
}

/*
 * add to busy list of queues for service, trying to be fair in ordering
 * the pending list according to last request service
 */
static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        cfq_log_cfqq(cfqd, cfqq, "add_to_rr");
        BUG_ON(cfq_cfqq_on_rr(cfqq));
        cfq_mark_cfqq_on_rr(cfqq);
        cfqd->busy_queues++;

        cfq_resort_rr_list(cfqd, cfqq);
}

/*
 * Called when the cfqq no longer has requests pending, remove it from
 * the service tree.
 */
static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
        BUG_ON(!cfq_cfqq_on_rr(cfqq));
        cfq_clear_cfqq_on_rr(cfqq);

        if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
                cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
                cfqq->service_tree = NULL;
        }
        if (cfqq->p_root) {
                rb_erase(&cfqq->p_node, cfqq->p_root);
                cfqq->p_root = NULL;
        }

        BUG_ON(!cfqd->busy_queues);
        cfqd->busy_queues--;
}

/*
 * rb tree support functions
 */
static void cfq_del_rq_rb(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);
        struct cfq_data *cfqd = cfqq->cfqd;
        const int sync = rq_is_sync(rq);

        BUG_ON(!cfqq->queued[sync]);
        cfqq->queued[sync]--;

        elv_rb_del(&cfqq->sort_list, rq);

        if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
                cfq_del_cfqq_rr(cfqd, cfqq);
}

static void cfq_add_rq_rb(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);
        struct cfq_data *cfqd = cfqq->cfqd;
        struct request *__alias, *prev;

        cfqq->queued[rq_is_sync(rq)]++;

        /*
         * looks a little odd, but the first insert might return an alias.
         * if that happens, put the alias on the dispatch list
         */
        while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)
                cfq_dispatch_insert(cfqd->queue, __alias);

        if (!cfq_cfqq_on_rr(cfqq))
                cfq_add_cfqq_rr(cfqd, cfqq);

        /*
         * check if this request is a better next-serve candidate
         */
        prev = cfqq->next_rq;
        cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);

        /*
         * adjust priority tree position, if ->next_rq changes
         */
        if (prev != cfqq->next_rq)
                cfq_prio_tree_add(cfqd, cfqq);

        BUG_ON(!cfqq->next_rq);
}

static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
{
        elv_rb_del(&cfqq->sort_list, rq);
        cfqq->queued[rq_is_sync(rq)]--;
        cfq_add_rq_rb(rq);
}

static struct request *
cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
{
        struct task_struct *tsk = current;
        struct cfq_io_context *cic;
        struct cfq_queue *cfqq;

        cic = cfq_cic_lookup(cfqd, tsk->io_context);
        if (!cic)
                return NULL;

        cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
        if (cfqq) {
                sector_t sector = bio->bi_sector + bio_sectors(bio);

                return elv_rb_find(&cfqq->sort_list, sector);
        }

        return NULL;
}

static void cfq_activate_request(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        cfqd->rq_in_driver[rq_is_sync(rq)]++;
        cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
                                                rq_in_driver(cfqd));

        cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
}

static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        const int sync = rq_is_sync(rq);

        WARN_ON(!cfqd->rq_in_driver[sync]);
        cfqd->rq_in_driver[sync]--;
        cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
                                                rq_in_driver(cfqd));
}

static void cfq_remove_request(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);

        if (cfqq->next_rq == rq)
                cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);

        list_del_init(&rq->queuelist);
        cfq_del_rq_rb(rq);

        cfqq->cfqd->rq_queued--;
        if (rq_is_meta(rq)) {
                WARN_ON(!cfqq->meta_pending);
                cfqq->meta_pending--;
        }
}

static int cfq_merge(struct request_queue *q, struct request **req,
                     struct bio *bio)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct request *__rq;

        __rq = cfq_find_rq_fmerge(cfqd, bio);
        if (__rq && elv_rq_merge_ok(__rq, bio)) {
                *req = __rq;
                return ELEVATOR_FRONT_MERGE;
        }

        return ELEVATOR_NO_MERGE;
}

static void cfq_merged_request(struct request_queue *q, struct request *req,
                               int type)
{
        if (type == ELEVATOR_FRONT_MERGE) {
                struct cfq_queue *cfqq = RQ_CFQQ(req);

                cfq_reposition_rq_rb(cfqq, req);
        }
}

static void
cfq_merged_requests(struct request_queue *q, struct request *rq,
                    struct request *next)
{
        /*
         * reposition in fifo if next is older than rq
         */
        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
            time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
                list_move(&rq->queuelist, &next->queuelist);
                rq_set_fifo_time(rq, rq_fifo_time(next));
        }

        cfq_remove_request(next);
}

static int cfq_allow_merge(struct request_queue *q, struct request *rq,
                           struct bio *bio)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_io_context *cic;
        struct cfq_queue *cfqq;

        /*
         * Disallow merge of a sync bio into an async request.
         */
        if (cfq_bio_sync(bio) && !rq_is_sync(rq))
                return false;

        /*
         * Lookup the cfqq that this bio will be queued with. Allow
         * merge only if rq is queued there.
         */
        cic = cfq_cic_lookup(cfqd, current->io_context);
        if (!cic)
                return false;

        cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
        return cfqq == RQ_CFQQ(rq);
}

static void __cfq_set_active_queue(struct cfq_data *cfqd,
                                   struct cfq_queue *cfqq)
{
        if (cfqq) {
                cfq_log_cfqq(cfqd, cfqq, "set_active");
                cfqq->slice_end = 0;
                cfqq->slice_dispatch = 0;

                cfq_clear_cfqq_wait_request(cfqq);
                cfq_clear_cfqq_must_dispatch(cfqq);
                cfq_clear_cfqq_must_alloc_slice(cfqq);
                cfq_clear_cfqq_fifo_expire(cfqq);
                cfq_mark_cfqq_slice_new(cfqq);

                del_timer(&cfqd->idle_slice_timer);
        }

        cfqd->active_queue = cfqq;
}

/*
 * current cfqq expired its slice (or was too idle), select new one
 */
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                    bool timed_out)
{
        cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);

        if (cfq_cfqq_wait_request(cfqq))
                del_timer(&cfqd->idle_slice_timer);

        cfq_clear_cfqq_wait_request(cfqq);

        /*
         * store what was left of this slice, if the queue idled/timed out
         */
        if (timed_out && !cfq_cfqq_slice_new(cfqq)) {
                cfqq->slice_resid = cfqq->slice_end - jiffies;
                cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
        }

        cfq_resort_rr_list(cfqd, cfqq);

        if (cfqq == cfqd->active_queue)
                cfqd->active_queue = NULL;

        if (cfqd->active_cic) {
                put_io_context(cfqd->active_cic->ioc);
                cfqd->active_cic = NULL;
        }
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
{
        struct cfq_queue *cfqq = cfqd->active_queue;

        if (cfqq)
                __cfq_slice_expired(cfqd, cfqq, timed_out);
}

/*
 * Get next queue for service. Unless we have a queue preemption,
 * we'll simply select the first cfqq in the service tree.
 */
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
{
        struct cfq_rb_root *service_tree =
                service_tree_for(cfqd->serving_prio, cfqd);

        if (RB_EMPTY_ROOT(&service_tree->rb))
                return NULL;
        return cfq_rb_first(service_tree);
}

/*
 * Get and set a new active queue for service.
 */
static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
                                              struct cfq_queue *cfqq)
{
        if (!cfqq)
                cfqq = cfq_get_next_queue(cfqd);

        __cfq_set_active_queue(cfqd, cfqq);
        return cfqq;
}

static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
                                          struct request *rq)
{
        if (blk_rq_pos(rq) >= cfqd->last_position)
                return blk_rq_pos(rq) - cfqd->last_position;
        else
                return cfqd->last_position - blk_rq_pos(rq);
}

#define CFQQ_SEEK_THR           8 * 1024
#define CFQQ_SEEKY(cfqq)        ((cfqq)->seek_mean > CFQQ_SEEK_THR)

static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                               struct request *rq)
{
        sector_t sdist = cfqq->seek_mean;

        if (!sample_valid(cfqq->seek_samples))
                sdist = CFQQ_SEEK_THR;

        return cfq_dist_from_last(cfqd, rq) <= sdist;
}

static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
                                    struct cfq_queue *cur_cfqq)
{
        struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];
        struct rb_node *parent, *node;
        struct cfq_queue *__cfqq;
        sector_t sector = cfqd->last_position;

        if (RB_EMPTY_ROOT(root))
                return NULL;

        /*
         * First, if we find a request starting at the end of the last
         * request, choose it.
         */
        __cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);
        if (__cfqq)
                return __cfqq;

        /*
         * If the exact sector wasn't found, the parent of the NULL leaf
         * will contain the closest sector.
         */
        __cfqq = rb_entry(parent, struct cfq_queue, p_node);
        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
                return __cfqq;

        if (blk_rq_pos(__cfqq->next_rq) < sector)
                node = rb_next(&__cfqq->p_node);
        else
                node = rb_prev(&__cfqq->p_node);
        if (!node)
                return NULL;

        __cfqq = rb_entry(node, struct cfq_queue, p_node);
        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
                return __cfqq;

        return NULL;
}

/*
 * cfqd - obvious
 * cur_cfqq - passed in so that we don't decide that the current queue is
 *            closely cooperating with itself.
 *
 * So, basically we're assuming that that cur_cfqq has dispatched at least
 * one request, and that cfqd->last_position reflects a position on the disk
 * associated with the I/O issued by cur_cfqq.  I'm not sure this is a valid
 * assumption.
 */
static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
                                              struct cfq_queue *cur_cfqq)
{
        struct cfq_queue *cfqq;

        if (!cfq_cfqq_sync(cur_cfqq))
                return NULL;
        if (CFQQ_SEEKY(cur_cfqq))
                return NULL;

        /*
         * We should notice if some of the queues are cooperating, eg
         * working closely on the same area of the disk. In that case,
         * we can group them together and don't waste time idling.
         */
        cfqq = cfqq_close(cfqd, cur_cfqq);
        if (!cfqq)
                return NULL;

        /*
         * It only makes sense to merge sync queues.
         */
        if (!cfq_cfqq_sync(cfqq))
                return NULL;
        if (CFQQ_SEEKY(cfqq))
                return NULL;

        /*
         * Do not merge queues of different priority classes
         */
        if (cfq_class_rt(cfqq) != cfq_class_rt(cur_cfqq))
                return NULL;

        return cfqq;
}

/*
 * Determine whether we should enforce idle window for this queue.
 */

static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        enum wl_prio_t prio = cfqq_prio(cfqq);
        struct cfq_rb_root *service_tree;

        /* We never do for idle class queues. */
        if (prio == IDLE_WORKLOAD)
                return false;

        /* We do for queues that were marked with idle window flag. */
        if (cfq_cfqq_idle_window(cfqq))
                return true;

        /*
         * Otherwise, we do only if they are the last ones
         * in their service tree.
         */
        service_tree = service_tree_for(prio, cfqd);
        if (service_tree->count == 0)
                return true;

        return (service_tree->count == 1 && cfq_rb_first(service_tree) == cfqq);
}

static void cfq_arm_slice_timer(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq = cfqd->active_queue;
        struct cfq_io_context *cic;
        unsigned long sl;

        /*
         * SSD device without seek penalty, disable idling. But only do so
         * for devices that support queuing, otherwise we still have a problem
         * with sync vs async workloads.
         */
        if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)
                return;

        WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
        WARN_ON(cfq_cfqq_slice_new(cfqq));

        /*
         * idle is disabled, either manually or by past process history
         */
        if (!cfqd->cfq_slice_idle || !cfq_should_idle(cfqd, cfqq))
                return;

        /*
         * still requests with the driver, don't idle
         */
        if (rq_in_driver(cfqd))
                return;

        /*
         * task has exited, don't wait
         */
        cic = cfqd->active_cic;
        if (!cic || !atomic_read(&cic->ioc->nr_tasks))
                return;

        /*
         * If our average think time is larger than the remaining time
         * slice, then don't idle. This avoids overrunning the allotted
         * time slice.
         */
        if (sample_valid(cic->ttime_samples) &&
            (cfqq->slice_end - jiffies < cic->ttime_mean))
                return;

        cfq_mark_cfqq_wait_request(cfqq);

        /*
         * we don't want to idle for seeks, but we do want to allow
         * fair distribution of slice time for a process doing back-to-back
         * seeks. so allow a little bit of time for him to submit a new rq
         */
        sl = cfqd->cfq_slice_idle;
        if (sample_valid(cfqq->seek_samples) && CFQQ_SEEKY(cfqq))
                sl = min(sl, msecs_to_jiffies(CFQ_MIN_TT));

        mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
        cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu", sl);
}

/*
 * Move request from internal lists to the request queue dispatch list.
 */
static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq = RQ_CFQQ(rq);

        cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");

        cfqq->next_rq = cfq_find_next_rq(cfqd, cfqq, rq);
        cfq_remove_request(rq);
        cfqq->dispatched++;
        elv_dispatch_sort(q, rq);

        if (cfq_cfqq_sync(cfqq))
                cfqd->sync_flight++;
}

/*
 * return expired entry, or NULL to just start from scratch in rbtree
 */
static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
{
        struct request *rq = NULL;

        if (cfq_cfqq_fifo_expire(cfqq))
                return NULL;

        cfq_mark_cfqq_fifo_expire(cfqq);

        if (list_empty(&cfqq->fifo))
                return NULL;

        rq = rq_entry_fifo(cfqq->fifo.next);
        if (time_before(jiffies, rq_fifo_time(rq)))
                rq = NULL;

        cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
        return rq;
}

static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        const int base_rq = cfqd->cfq_slice_async_rq;

        WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

        return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));
}

/*
 * Must be called with the queue_lock held.
 */
static int cfqq_process_refs(struct cfq_queue *cfqq)
{
        int process_refs, io_refs;

        io_refs = cfqq->allocated[READ] + cfqq->allocated[WRITE];
        process_refs = atomic_read(&cfqq->ref) - io_refs;
        BUG_ON(process_refs < 0);
        return process_refs;
}

static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
{
        int process_refs, new_process_refs;
        struct cfq_queue *__cfqq;

        /* Avoid a circular list and skip interim queue merges */
        while ((__cfqq = new_cfqq->new_cfqq)) {
                if (__cfqq == cfqq)
                        return;
                new_cfqq = __cfqq;
        }

        process_refs = cfqq_process_refs(cfqq);
        /*
         * If the process for the cfqq has gone away, there is no
         * sense in merging the queues.
         */
        if (process_refs == 0)
                return;

        /*
         * Merge in the direction of the lesser amount of work.
         */
        new_process_refs = cfqq_process_refs(new_cfqq);
        if (new_process_refs >= process_refs) {
                cfqq->new_cfqq = new_cfqq;
                atomic_add(process_refs, &new_cfqq->ref);
        } else {
                new_cfqq->new_cfqq = cfqq;
                atomic_add(new_process_refs, &cfqq->ref);
        }
}

/*
 * Select a queue for service. If we have a current active queue,
 * check whether to continue servicing it, or retrieve and set a new one.
 */
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq, *new_cfqq = NULL;

        cfqq = cfqd->active_queue;
        if (!cfqq)
                goto new_queue;

        /*
         * The active queue has run out of time, expire it and select new.
         */
        if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq))
                goto expire;

        /*
         * The active queue has requests and isn't expired, allow it to
         * dispatch.
         */
        if (!RB_EMPTY_ROOT(&cfqq->sort_list))
                goto keep_queue;

        /*
         * If another queue has a request waiting within our mean seek
         * distance, let it run.  The expire code will check for close
         * cooperators and put the close queue at the front of the service
         * tree.  If possible, merge the expiring queue with the new cfqq.
         */
        new_cfqq = cfq_close_cooperator(cfqd, cfqq);
        if (new_cfqq) {
                if (!cfqq->new_cfqq)
                        cfq_setup_merge(cfqq, new_cfqq);
                goto expire;
        }

        /*
         * No requests pending. If the active queue still has requests in
         * flight or is idling for a new request, allow either of these
         * conditions to happen (or time out) before selecting a new queue.
         */
        if (timer_pending(&cfqd->idle_slice_timer) ||
            (cfqq->dispatched && cfq_should_idle(cfqd, cfqq))) {
                cfqq = NULL;
                goto keep_queue;
        }

expire:
        cfq_slice_expired(cfqd, 0);
new_queue:
        if (!new_cfqq) {
                if (cfq_busy_queues_wl(RT_WORKLOAD, cfqd))
                        cfqd->serving_prio = RT_WORKLOAD;
                else if (cfq_busy_queues_wl(BE_WORKLOAD, cfqd))
                        cfqd->serving_prio = BE_WORKLOAD;
                else
                        cfqd->serving_prio = IDLE_WORKLOAD;
        }
        cfqq = cfq_set_active_queue(cfqd, new_cfqq);
keep_queue:
        return cfqq;
}

static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
{
        int dispatched = 0;

        while (cfqq->next_rq) {
                cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
                dispatched++;
        }

        BUG_ON(!list_empty(&cfqq->fifo));
        return dispatched;
}

/*
 * Drain our current requests. Used for barriers and when switching
 * io schedulers on-the-fly.
 */
static int cfq_forced_dispatch(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq;
        int dispatched = 0;
        int i;
        for (i = 0; i < 2; ++i)
                while ((cfqq = cfq_rb_first(&cfqd->service_trees[i])) != NULL)
                        dispatched += __cfq_forced_dispatch_cfqq(cfqq);

        while ((cfqq = cfq_rb_first(&cfqd->service_tree_idle)) != NULL)
                dispatched += __cfq_forced_dispatch_cfqq(cfqq);

        cfq_slice_expired(cfqd, 0);

        BUG_ON(cfqd->busy_queues);

        cfq_log(cfqd, "forced_dispatch=%d", dispatched);
        return dispatched;
}

static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        unsigned int max_dispatch;

        /*
         * Drain async requests before we start sync IO
         */
        if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC])
                return false;

        /*
         * If this is an async queue and we have sync IO in flight, let it wait
         */
        if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
                return false;

        max_dispatch = cfqd->cfq_quantum;
        if (cfq_class_idle(cfqq))
                max_dispatch = 1;

        /*
         * Does this cfqq already have too much IO in flight?
         */
        if (cfqq->dispatched >= max_dispatch) {
                /*
                 * idle queue must always only have a single IO in flight
                 */
                if (cfq_class_idle(cfqq))
                        return false;

                /*
                 * We have other queues, don't allow more IO from this one
                 */
                if (cfqd->busy_queues > 1)
                        return false;

                /*
                 * Sole queue user, allow bigger slice
                 */
                max_dispatch *= 4;
        }

        /*
         * Async queues must wait a bit before being allowed dispatch.
         * We also ramp up the dispatch depth gradually for async IO,
         * based on the last sync IO we serviced
         */
        if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
                unsigned long last_sync = jiffies - cfqd->last_end_sync_rq;
                unsigned int depth;

                depth = last_sync / cfqd->cfq_slice[1];
                if (!depth && !cfqq->dispatched)
                        depth = 1;
                if (depth < max_dispatch)
                        max_dispatch = depth;
        }

        /*
         * If we're below the current max, allow a dispatch
         */
        return cfqq->dispatched < max_dispatch;
}

/*
 * Dispatch a request from cfqq, moving them to the request queue
 * dispatch list.
 */
static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        struct request *rq;

        BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));

        if (!cfq_may_dispatch(cfqd, cfqq))
                return false;

        /*
         * follow expired path, else get first next available
         */
        rq = cfq_check_fifo(cfqq);
        if (!rq)
                rq = cfqq->next_rq;

        /*
         * insert request into driver dispatch list
         */
        cfq_dispatch_insert(cfqd->queue, rq);

        if (!cfqd->active_cic) {
                struct cfq_io_context *cic = RQ_CIC(rq);

                atomic_long_inc(&cic->ioc->refcount);
                cfqd->active_cic = cic;
        }

        return true;
}

/*
 * Find the cfqq that we need to service and move a request from that to the
 * dispatch list
 */
static int cfq_dispatch_requests(struct request_queue *q, int force)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq;

        if (!cfqd->busy_queues)
                return 0;

        if (unlikely(force))
                return cfq_forced_dispatch(cfqd);

        cfqq = cfq_select_queue(cfqd);
        if (!cfqq)
                return 0;

        /*
         * Dispatch a request from this cfqq, if it is allowed
         */
        if (!cfq_dispatch_request(cfqd, cfqq))
                return 0;

        cfqq->slice_dispatch++;
        cfq_clear_cfqq_must_dispatch(cfqq);

        /*
         * expire an async queue immediately if it has used up its slice. idle
         * queue always expire after 1 dispatch round.
         */
        if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
            cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
            cfq_class_idle(cfqq))) {
                cfqq->slice_end = jiffies + 1;
                cfq_slice_expired(cfqd, 0);
        }

        cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
        return 1;
}

/*
 * task holds one reference to the queue, dropped when task exits. each rq
 * in-flight on this queue also holds a reference, dropped when rq is freed.
 *
 * queue lock must be held here.
 */
static void cfq_put_queue(struct cfq_queue *cfqq)
{
        struct cfq_data *cfqd = cfqq->cfqd;

        BUG_ON(atomic_read(&cfqq->ref) <= 0);

        if (!atomic_dec_and_test(&cfqq->ref))
                return;

        cfq_log_cfqq(cfqd, cfqq, "put_queue");
        BUG_ON(rb_first(&cfqq->sort_list));
        BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
        BUG_ON(cfq_cfqq_on_rr(cfqq));

        if (unlikely(cfqd->active_queue == cfqq)) {
                __cfq_slice_expired(cfqd, cfqq, 0);
                cfq_schedule_dispatch(cfqd);
        }

        kmem_cache_free(cfq_pool, cfqq);
}

/*
 * Must always be called with the rcu_read_lock() held
 */
static void
__call_for_each_cic(struct io_context *ioc,
                    void (*func)(struct io_context *, struct cfq_io_context *))
{
        struct cfq_io_context *cic;
        struct hlist_node *n;

        hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
                func(ioc, cic);
}

/*
 * Call func for each cic attached to this ioc.
 */
static void
call_for_each_cic(struct io_context *ioc,
                  void (*func)(struct io_context *, struct cfq_io_context *))
{
        rcu_read_lock();
        __call_for_each_cic(ioc, func);
        rcu_read_unlock();
}

static void cfq_cic_free_rcu(struct rcu_head *head)
{
        struct cfq_io_context *cic;

        cic = container_of(head, struct cfq_io_context, rcu_head);

        kmem_cache_free(cfq_ioc_pool, cic);
        elv_ioc_count_dec(cfq_ioc_count);

        if (ioc_gone) {
                /*
                 * CFQ scheduler is exiting, grab exit lock and check
                 * the pending io context count. If it hits zero,
                 * complete ioc_gone and set it back to NULL
                 */
                spin_lock(&ioc_gone_lock);
                if (ioc_gone && !elv_ioc_count_read(cfq_ioc_count)) {
                        complete(ioc_gone);
                        ioc_gone = NULL;
                }
                spin_unlock(&ioc_gone_lock);
        }
}

static void cfq_cic_free(struct cfq_io_context *cic)
{
        call_rcu(&cic->rcu_head, cfq_cic_free_rcu);
}

static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
{
        unsigned long flags;

        BUG_ON(!cic->dead_key);

        spin_lock_irqsave(&ioc->lock, flags);
        radix_tree_delete(&ioc->radix_root, cic->dead_key);
        hlist_del_rcu(&cic->cic_list);
        spin_unlock_irqrestore(&ioc->lock, flags);

        cfq_cic_free(cic);
}

/*
 * Must be called with rcu_read_lock() held or preemption otherwise disabled.
 * Only two callers of this - ->dtor() which is called with the rcu_read_lock(),
 * and ->trim() which is called with the task lock held
 */
static void cfq_free_io_context(struct io_context *ioc)
{
        /*
         * ioc->refcount is zero here, or we are called from elv_unregister(),
         * so no more cic's are allowed to be linked into this ioc.  So it
         * should be ok to iterate over the known list, we will see all cic's
         * since no new ones are added.
         */
        __call_for_each_cic(ioc, cic_free_func);
}

static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        struct cfq_queue *__cfqq, *next;

        if (unlikely(cfqq == cfqd->active_queue)) {
                __cfq_slice_expired(cfqd, cfqq, 0);
                cfq_schedule_dispatch(cfqd);
        }

        /*
         * If this queue was scheduled to merge with another queue, be
         * sure to drop the reference taken on that queue (and others in
         * the merge chain).  See cfq_setup_merge and cfq_merge_cfqqs.
         */
        __cfqq = cfqq->new_cfqq;
        while (__cfqq) {
                if (__cfqq == cfqq) {
                        WARN(1, "cfqq->new_cfqq loop detected\n");
                        break;
                }
                next = __cfqq->new_cfqq;
                cfq_put_queue(__cfqq);
                __cfqq = next;
        }

        cfq_put_queue(cfqq);
}

static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
                                         struct cfq_io_context *cic)
{
        struct io_context *ioc = cic->ioc;

        list_del_init(&cic->queue_list);

        /*
         * Make sure key == NULL is seen for dead queues
         */
        smp_wmb();
        cic->dead_key = (unsigned long) cic->key;
        cic->key = NULL;

        if (ioc->ioc_data == cic)
                rcu_assign_pointer(ioc->ioc_data, NULL);

        if (cic->cfqq[BLK_RW_ASYNC]) {
                cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
                cic->cfqq[BLK_RW_ASYNC] = NULL;
        }

        if (cic->cfqq[BLK_RW_SYNC]) {
                cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_SYNC]);
                cic->cfqq[BLK_RW_SYNC] = NULL;
        }
}

static void cfq_exit_single_io_context(struct io_context *ioc,
                                       struct cfq_io_context *cic)
{
        struct cfq_data *cfqd = cic->key;

        if (cfqd) {
                struct request_queue *q = cfqd->queue;
                unsigned long flags;

                spin_lock_irqsave(q->queue_lock, flags);

                /*
                 * Ensure we get a fresh copy of the ->key to prevent
                 * race between exiting task and queue
                 */
                smp_read_barrier_depends();
                if (cic->key)
                        __cfq_exit_single_io_context(cfqd, cic);

                spin_unlock_irqrestore(q->queue_lock, flags);
        }
}

/*
 * The process that ioc belongs to has exited, we need to clean up
 * and put the internal structures we have that belongs to that process.
 */
static void cfq_exit_io_context(struct io_context *ioc)
{
        call_for_each_cic(ioc, cfq_exit_single_io_context);
}

static struct cfq_io_context *
cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
        struct cfq_io_context *cic;

        cic = kmem_cache_alloc_node(cfq_ioc_pool, gfp_mask | __GFP_ZERO,
                                                        cfqd->queue->node);
        if (cic) {
                cic->last_end_request = jiffies;
                INIT_LIST_HEAD(&cic->queue_list);
                INIT_HLIST_NODE(&cic->cic_list);
                cic->dtor = cfq_free_io_context;
                cic->exit = cfq_exit_io_context;
                elv_ioc_count_inc(cfq_ioc_count);
        }

        return cic;
}

static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
{
        struct task_struct *tsk = current;
        int ioprio_class;

        if (!cfq_cfqq_prio_changed(cfqq))
                return;

        ioprio_class = IOPRIO_PRIO_CLASS(ioc->ioprio);
        switch (ioprio_class) {
        default:
                printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
        case IOPRIO_CLASS_NONE:
                /*
                 * no prio set, inherit CPU scheduling settings
                 */
                cfqq->ioprio = task_nice_ioprio(tsk);
                cfqq->ioprio_class = task_nice_ioclass(tsk);
                break;
        case IOPRIO_CLASS_RT:
                cfqq->ioprio = task_ioprio(ioc);
                cfqq->ioprio_class = IOPRIO_CLASS_RT;
                break;
        case IOPRIO_CLASS_BE:
                cfqq->ioprio = task_ioprio(ioc);
                cfqq->ioprio_class = IOPRIO_CLASS_BE;
                break;
        case IOPRIO_CLASS_IDLE:
                cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
                cfqq->ioprio = 7;
                cfq_clear_cfqq_idle_window(cfqq);
                break;
        }

        /*
         * keep track of original prio settings in case we have to temporarily
         * elevate the priority of this queue
         */
        cfqq->org_ioprio = cfqq->ioprio;
        cfqq->org_ioprio_class = cfqq->ioprio_class;
        cfq_clear_cfqq_prio_changed(cfqq);
}

static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
{
        struct cfq_data *cfqd = cic->key;
        struct cfq_queue *cfqq;
        unsigned long flags;

        if (unlikely(!cfqd))
                return;

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);

        cfqq = cic->cfqq[BLK_RW_ASYNC];
        if (cfqq) {
                struct cfq_queue *new_cfqq;
                new_cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic->ioc,
                                                GFP_ATOMIC);
                if (new_cfqq) {
                        cic->cfqq[BLK_RW_ASYNC] = new_cfqq;
                        cfq_put_queue(cfqq);
                }
        }

        cfqq = cic->cfqq[BLK_RW_SYNC];
        if (cfqq)
                cfq_mark_cfqq_prio_changed(cfqq);

        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_ioc_set_ioprio(struct io_context *ioc)
{
        call_for_each_cic(ioc, changed_ioprio);
        ioc->ioprio_changed = 0;
}

static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                          pid_t pid, bool is_sync)
{
        RB_CLEAR_NODE(&cfqq->rb_node);
        RB_CLEAR_NODE(&cfqq->p_node);
        INIT_LIST_HEAD(&cfqq->fifo);

        atomic_set(&cfqq->ref, 0);
        cfqq->cfqd = cfqd;

        cfq_mark_cfqq_prio_changed(cfqq);

        if (is_sync) {
                if (!cfq_class_idle(cfqq))
                        cfq_mark_cfqq_idle_window(cfqq);
                cfq_mark_cfqq_sync(cfqq);
        }
        cfqq->pid = pid;
}

static struct cfq_queue *
cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync,
                     struct io_context *ioc, gfp_t gfp_mask)
{
        struct cfq_queue *cfqq, *new_cfqq = NULL;
        struct cfq_io_context *cic;

retry:
        cic = cfq_cic_lookup(cfqd, ioc);
        /* cic always exists here */
        cfqq = cic_to_cfqq(cic, is_sync);

        /*
         * Always try a new alloc if we fell back to the OOM cfqq
         * originally, since it should just be a temporary situation.
         */
        if (!cfqq || cfqq == &cfqd->oom_cfqq) {
                cfqq = NULL;
                if (new_cfqq) {
                        cfqq = new_cfqq;
                        new_cfqq = NULL;
                } else if (gfp_mask & __GFP_WAIT) {
                        spin_unlock_irq(cfqd->queue->queue_lock);
                        new_cfqq = kmem_cache_alloc_node(cfq_pool,
                                        gfp_mask | __GFP_ZERO,
                                        cfqd->queue->node);
                        spin_lock_irq(cfqd->queue->queue_lock);
                        if (new_cfqq)
                                goto retry;
                } else {
                        cfqq = kmem_cache_alloc_node(cfq_pool,
                                        gfp_mask | __GFP_ZERO,
                                        cfqd->queue->node);
                }

                if (cfqq) {
                        cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
                        cfq_init_prio_data(cfqq, ioc);
                        cfq_log_cfqq(cfqd, cfqq, "alloced");
                } else
                        cfqq = &cfqd->oom_cfqq;
        }

        if (new_cfqq)
                kmem_cache_free(cfq_pool, new_cfqq);

        return cfqq;
}

static struct cfq_queue **
cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
{
        switch (ioprio_class) {
        case IOPRIO_CLASS_RT:
                return &cfqd->async_cfqq[0][ioprio];
        case IOPRIO_CLASS_BE:
                return &cfqd->async_cfqq[1][ioprio];
        case IOPRIO_CLASS_IDLE:
                return &cfqd->async_idle_cfqq;
        default:
                BUG();
        }
}

static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct io_context *ioc,
              gfp_t gfp_mask)
{
        const int ioprio = task_ioprio(ioc);
        const int ioprio_class = task_ioprio_class(ioc);
        struct cfq_queue **async_cfqq = NULL;
        struct cfq_queue *cfqq = NULL;

        if (!is_sync) {
                async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
                cfqq = *async_cfqq;
        }

        if (!cfqq)
                cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);

        /*
         * pin the queue now that it's allocated, scheduler exit will prune it
         */
        if (!is_sync && !(*async_cfqq)) {
                atomic_inc(&cfqq->ref);
                *async_cfqq = cfqq;
        }

        atomic_inc(&cfqq->ref);
        return cfqq;
}

/*
 * We drop cfq io contexts lazily, so we may find a dead one.
 */
static void
cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
                  struct cfq_io_context *cic)
{
        unsigned long flags;

        WARN_ON(!list_empty(&cic->queue_list));

        spin_lock_irqsave(&ioc->lock, flags);

        BUG_ON(ioc->ioc_data == cic);

        radix_tree_delete(&ioc->radix_root, (unsigned long) cfqd);
        hlist_del_rcu(&cic->cic_list);
        spin_unlock_irqrestore(&ioc->lock, flags);

        cfq_cic_free(cic);
}

static struct cfq_io_context *
cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
{
        struct cfq_io_context *cic;
        unsigned long flags;
        void *k;

        if (unlikely(!ioc))
                return NULL;

        rcu_read_lock();

        /*
         * we maintain a last-hit cache, to avoid browsing over the tree
         */
        cic = rcu_dereference(ioc->ioc_data);
        if (cic && cic->key == cfqd) {
                rcu_read_unlock();
                return cic;
        }

        do {
                cic = radix_tree_lookup(&ioc->radix_root, (unsigned long) cfqd);
                rcu_read_unlock();
                if (!cic)
                        break;
                /* ->key must be copied to avoid race with cfq_exit_queue() */
                k = cic->key;
                if (unlikely(!k)) {
                        cfq_drop_dead_cic(cfqd, ioc, cic);
                        rcu_read_lock();
                        continue;
                }

                spin_lock_irqsave(&ioc->lock, flags);
                rcu_assign_pointer(ioc->ioc_data, cic);
                spin_unlock_irqrestore(&ioc->lock, flags);
                break;
        } while (1);

        return cic;
}

/*
 * Add cic into ioc, using cfqd as the search key. This enables us to lookup
 * the process specific cfq io context when entered from the block layer.
 * Also adds the cic to a per-cfqd list, used when this queue is removed.
 */
static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
                        struct cfq_io_context *cic, gfp_t gfp_mask)
{
        unsigned long flags;
        int ret;

        ret = radix_tree_preload(gfp_mask);
        if (!ret) {
                cic->ioc = ioc;
                cic->key = cfqd;

                spin_lock_irqsave(&ioc->lock, flags);
                ret = radix_tree_insert(&ioc->radix_root,
                                                (unsigned long) cfqd, cic);
                if (!ret)
                        hlist_add_head_rcu(&cic->cic_list, &ioc->cic_list);
                spin_unlock_irqrestore(&ioc->lock, flags);

                radix_tree_preload_end();

                if (!ret) {
                        spin_lock_irqsave(cfqd->queue->queue_lock, flags);
                        list_add(&cic->queue_list, &cfqd->cic_list);
                        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
                }
        }

        if (ret)
                printk(KERN_ERR "cfq: cic link failed!\n");

        return ret;
}

/*
 * Setup general io context and cfq io context. There can be several cfq
 * io contexts per general io context, if this process is doing io to more
 * than one device managed by cfq.
 */
static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
        struct io_context *ioc = NULL;
        struct cfq_io_context *cic;

        might_sleep_if(gfp_mask & __GFP_WAIT);

        ioc = get_io_context(gfp_mask, cfqd->queue->node);
        if (!ioc)
                return NULL;

        cic = cfq_cic_lookup(cfqd, ioc);
        if (cic)
                goto out;

        cic = cfq_alloc_io_context(cfqd, gfp_mask);
        if (cic == NULL)
                goto err;

        if (cfq_cic_link(cfqd, ioc, cic, gfp_mask))
                goto err_free;

out:
        smp_read_barrier_depends();
        if (unlikely(ioc->ioprio_changed))
                cfq_ioc_set_ioprio(ioc);

        return cic;
err_free:
        cfq_cic_free(cic);
err:
        put_io_context(ioc);
        return NULL;
}

static void
cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
{
        unsigned long elapsed = jiffies - cic->last_end_request;
        unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);

        cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
        cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
        cic->ttime_mean = (cic->ttime_total + 128) / cic->ttime_samples;
}

static void
cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                       struct request *rq)
{
        sector_t sdist;
        u64 total;

        if (!cfqq->last_request_pos)
                sdist = 0;
        else if (cfqq->last_request_pos < blk_rq_pos(rq))
                sdist = blk_rq_pos(rq) - cfqq->last_request_pos;
        else
                sdist = cfqq->last_request_pos - blk_rq_pos(rq);

        /*
         * Don't allow the seek distance to get too large from the
         * odd fragment, pagein, etc
         */
        if (cfqq->seek_samples <= 60) /* second&third seek */
                sdist = min(sdist, (cfqq->seek_mean * 4) + 2*1024*1024);
        else
                sdist = min(sdist, (cfqq->seek_mean * 4) + 2*1024*64);

        cfqq->seek_samples = (7*cfqq->seek_samples + 256) / 8;
        cfqq->seek_total = (7*cfqq->seek_total + (u64)256*sdist) / 8;
        total = cfqq->seek_total + (cfqq->seek_samples/2);
        do_div(total, cfqq->seek_samples);
        cfqq->seek_mean = (sector_t)total;

        /*
         * If this cfqq is shared between multiple processes, check to
         * make sure that those processes are still issuing I/Os within
         * the mean seek distance.  If not, it may be time to break the
         * queues apart again.
         */
        if (cfq_cfqq_coop(cfqq)) {
                if (CFQQ_SEEKY(cfqq) && !cfqq->seeky_start)
                        cfqq->seeky_start = jiffies;
                else if (!CFQQ_SEEKY(cfqq))
                        cfqq->seeky_start = 0;
        }
}

/*
 * Disable idle window if the process thinks too long or seeks so much that
 * it doesn't matter
 */
static void
cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                       struct cfq_io_context *cic)
{
        int old_idle, enable_idle;

        /*
         * Don't idle for async or idle io prio class
         */
        if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq))
                return;

        enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);

        if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
            (!cfqd->cfq_latency && cfqd->hw_tag && CFQQ_SEEKY(cfqq)))
                enable_idle = 0;
        else if (sample_valid(cic->ttime_samples)) {
                unsigned int slice_idle = cfqd->cfq_slice_idle;
                if (sample_valid(cfqq->seek_samples) && CFQQ_SEEKY(cfqq))
                        slice_idle = msecs_to_jiffies(CFQ_MIN_TT);
                if (cic->ttime_mean > slice_idle)
                        enable_idle = 0;
                else
                        enable_idle = 1;
        }

        if (old_idle != enable_idle) {
                cfq_log_cfqq(cfqd, cfqq, "idle=%d", enable_idle);
                if (enable_idle)
                        cfq_mark_cfqq_idle_window(cfqq);
                else
                        cfq_clear_cfqq_idle_window(cfqq);
        }
}

/*
 * Check if new_cfqq should preempt the currently active queue. Return 0 for
 * no or if we aren't sure, a 1 will cause a preempt.
 */
static bool
cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
                   struct request *rq)
{
        struct cfq_queue *cfqq;

        cfqq = cfqd->active_queue;
        if (!cfqq)
                return false;

        if (cfq_slice_used(cfqq))
                return true;

        if (cfq_class_idle(new_cfqq))
                return false;

        if (cfq_class_idle(cfqq))
                return true;

        /*
         * if the new request is sync, but the currently running queue is
         * not, let the sync request have priority.
         */
        if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
                return true;

        /*
         * So both queues are sync. Let the new request get disk time if
         * it's a metadata request and the current queue is doing regular IO.
         */
        if (rq_is_meta(rq) && !cfqq->meta_pending)
                return false;

        /*
         * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
         */
        if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
                return true;

        if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
                return false;

        /*
         * if this request is as-good as one we would expect from the
         * current cfqq, let it preempt
         */
        if (cfq_rq_close(cfqd, cfqq, rq))
                return true;

        return false;
}

/*
 * cfqq preempts the active queue. if we allowed preempt with no slice left,
 * let it have half of its nominal slice.
 */
static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        cfq_log_cfqq(cfqd, cfqq, "preempt");
        cfq_slice_expired(cfqd, 1);

        /*
         * Put the new queue at the front of the of the current list,
         * so we know that it will be selected next.
         */
        BUG_ON(!cfq_cfqq_on_rr(cfqq));

        cfq_service_tree_add(cfqd, cfqq, 1);

        cfqq->slice_end = 0;
        cfq_mark_cfqq_slice_new(cfqq);
}

/*
 * Called when a new fs request (rq) is added (to cfqq). Check if there's
 * something we should do about it
 */
static void
cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                struct request *rq)
{
        struct cfq_io_context *cic = RQ_CIC(rq);

        cfqd->rq_queued++;
        if (rq_is_meta(rq))
                cfqq->meta_pending++;

        cfq_update_io_thinktime(cfqd, cic);
        cfq_update_io_seektime(cfqd, cfqq, rq);
        cfq_update_idle_window(cfqd, cfqq, cic);

        cfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);

        if (cfqq == cfqd->active_queue) {
                /*
                 * Remember that we saw a request from this process, but
                 * don't start queuing just yet. Otherwise we risk seeing lots
                 * of tiny requests, because we disrupt the normal plugging
                 * and merging. If the request is already larger than a single
                 * page, let it rip immediately. For that case we assume that
                 * merging is already done. Ditto for a busy system that
                 * has other work pending, don't risk delaying until the
                 * idle timer unplug to continue working.
                 */
                if (cfq_cfqq_wait_request(cfqq)) {
                        if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
                            cfqd->busy_queues > 1) {
                                del_timer(&cfqd->idle_slice_timer);
                        __blk_run_queue(cfqd->queue);
                        }
                        cfq_mark_cfqq_must_dispatch(cfqq);
                }
        } else if (cfq_should_preempt(cfqd, cfqq, rq)) {
                /*
                 * not the active queue - expire current slice if it is
                 * idle and has expired it's mean thinktime or this new queue
                 * has some old slice time left and is of higher priority or
                 * this new queue is RT and the current one is BE
                 */
                cfq_preempt_queue(cfqd, cfqq);
                __blk_run_queue(cfqd->queue);
        }
}

static void cfq_insert_request(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq = RQ_CFQQ(rq);

        cfq_log_cfqq(cfqd, cfqq, "insert_request");
        cfq_init_prio_data(cfqq, RQ_CIC(rq)->ioc);

        rq_set_fifo_time(rq, jiffies + cfqd->cfq_fifo_expire[rq_is_sync(rq)]);
        list_add_tail(&rq->queuelist, &cfqq->fifo);
        cfq_add_rq_rb(rq);

        cfq_rq_enqueued(cfqd, cfqq, rq);
}

/*
 * Update hw_tag based on peak queue depth over 50 samples under
 * sufficient load.
 */
static void cfq_update_hw_tag(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq = cfqd->active_queue;

        if (rq_in_driver(cfqd) > cfqd->rq_in_driver_peak)
                cfqd->rq_in_driver_peak = rq_in_driver(cfqd);

        if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
            rq_in_driver(cfqd) <= CFQ_HW_QUEUE_MIN)
                return;

        /*
         * If active queue hasn't enough requests and can idle, cfq might not
         * dispatch sufficient requests to hardware. Don't zero hw_tag in this
         * case
         */
        if (cfqq && cfq_cfqq_idle_window(cfqq) &&
            cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
            CFQ_HW_QUEUE_MIN && rq_in_driver(cfqd) < CFQ_HW_QUEUE_MIN)
                return;

        if (cfqd->hw_tag_samples++ < 50)
                return;

        if (cfqd->rq_in_driver_peak >= CFQ_HW_QUEUE_MIN)
                cfqd->hw_tag = 1;
        else
                cfqd->hw_tag = 0;

        cfqd->hw_tag_samples = 0;
        cfqd->rq_in_driver_peak = 0;
}

static void cfq_completed_request(struct request_queue *q, struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);
        struct cfq_data *cfqd = cfqq->cfqd;
        const int sync = rq_is_sync(rq);
        unsigned long now;

        now = jiffies;
        cfq_log_cfqq(cfqd, cfqq, "complete");

        cfq_update_hw_tag(cfqd);

        WARN_ON(!cfqd->rq_in_driver[sync]);
        WARN_ON(!cfqq->dispatched);
        cfqd->rq_in_driver[sync]--;
        cfqq->dispatched--;

        if (cfq_cfqq_sync(cfqq))
                cfqd->sync_flight--;

        if (sync) {
                RQ_CIC(rq)->last_end_request = now;
                cfqd->last_end_sync_rq = now;
        }

        /*
         * If this is the active queue, check if it needs to be expired,
         * or if we want to idle in case it has no pending requests.
         */
        if (cfqd->active_queue == cfqq) {
                const bool cfqq_empty = RB_EMPTY_ROOT(&cfqq->sort_list);

                if (cfq_cfqq_slice_new(cfqq)) {
                        cfq_set_prio_slice(cfqd, cfqq);
                        cfq_clear_cfqq_slice_new(cfqq);
                }
                /*
                 * If there are no requests waiting in this queue, and
                 * there are other queues ready to issue requests, AND
                 * those other queues are issuing requests within our
                 * mean seek distance, give them a chance to run instead
                 * of idling.
                 */
                if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
                        cfq_slice_expired(cfqd, 1);
                else if (cfqq_empty && !cfq_close_cooperator(cfqd, cfqq) &&
                         sync && !rq_noidle(rq))
                        cfq_arm_slice_timer(cfqd);
        }

        if (!rq_in_driver(cfqd))
                cfq_schedule_dispatch(cfqd);
}

/*
 * we temporarily boost lower priority queues if they are holding fs exclusive
 * resources. they are boosted to normal prio (CLASS_BE/4)
 */
static void cfq_prio_boost(struct cfq_queue *cfqq)
{
        if (has_fs_excl()) {
                /*
                 * boost idle prio on transactions that would lock out other
                 * users of the filesystem
                 */
                if (cfq_class_idle(cfqq))
                        cfqq->ioprio_class = IOPRIO_CLASS_BE;
                if (cfqq->ioprio > IOPRIO_NORM)
                        cfqq->ioprio = IOPRIO_NORM;
        } else {
                /*
                 * check if we need to unboost the queue
                 */
                if (cfqq->ioprio_class != cfqq->org_ioprio_class)
                        cfqq->ioprio_class = cfqq->org_ioprio_class;
                if (cfqq->ioprio != cfqq->org_ioprio)
                        cfqq->ioprio = cfqq->org_ioprio;
        }
}

static inline int __cfq_may_queue(struct cfq_queue *cfqq)
{
        if (cfq_cfqq_wait_request(cfqq) && !cfq_cfqq_must_alloc_slice(cfqq)) {
                cfq_mark_cfqq_must_alloc_slice(cfqq);
                return ELV_MQUEUE_MUST;
        }

        return ELV_MQUEUE_MAY;
}

static int cfq_may_queue(struct request_queue *q, int rw)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct task_struct *tsk = current;
        struct cfq_io_context *cic;
        struct cfq_queue *cfqq;

        /*
         * don't force setup of a queue from here, as a call to may_queue
         * does not necessarily imply that a request actually will be queued.
         * so just lookup a possibly existing queue, or return 'may queue'
         * if that fails
         */
        cic = cfq_cic_lookup(cfqd, tsk->io_context);
        if (!cic)
                return ELV_MQUEUE_MAY;

        cfqq = cic_to_cfqq(cic, rw_is_sync(rw));
        if (cfqq) {
                cfq_init_prio_data(cfqq, cic->ioc);
                cfq_prio_boost(cfqq);

                return __cfq_may_queue(cfqq);
        }

        return ELV_MQUEUE_MAY;
}

/*
 * queue lock held here
 */
static void cfq_put_request(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);

        if (cfqq) {
                const int rw = rq_data_dir(rq);

                BUG_ON(!cfqq->allocated[rw]);
                cfqq->allocated[rw]--;

                put_io_context(RQ_CIC(rq)->ioc);

                rq->elevator_private = NULL;
                rq->elevator_private2 = NULL;

                cfq_put_queue(cfqq);
        }
}

static struct cfq_queue *
cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_context *cic,
                struct cfq_queue *cfqq)
{
        cfq_log_cfqq(cfqd, cfqq, "merging with queue %p", cfqq->new_cfqq);
        cic_set_cfqq(cic, cfqq->new_cfqq, 1);
        cfq_mark_cfqq_coop(cfqq->new_cfqq);
        cfq_put_queue(cfqq);
        return cic_to_cfqq(cic, 1);
}

static int should_split_cfqq(struct cfq_queue *cfqq)
{
        if (cfqq->seeky_start &&
            time_after(jiffies, cfqq->seeky_start + CFQQ_COOP_TOUT))
                return 1;
        return 0;
}

/*
 * Returns NULL if a new cfqq should be allocated, or the old cfqq if this
 * was the last process referring to said cfqq.
 */
static struct cfq_queue *
split_cfqq(struct cfq_io_context *cic, struct cfq_queue *cfqq)
{
        if (cfqq_process_refs(cfqq) == 1) {
                cfqq->seeky_start = 0;
                cfqq->pid = current->pid;
                cfq_clear_cfqq_coop(cfqq);
                return cfqq;
        }

        cic_set_cfqq(cic, NULL, 1);
        cfq_put_queue(cfqq);
        return NULL;
}
/*
 * Allocate cfq data structures associated with this request.
 */
static int
cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_io_context *cic;
        const int rw = rq_data_dir(rq);
        const bool is_sync = rq_is_sync(rq);
        struct cfq_queue *cfqq;
        unsigned long flags;

        might_sleep_if(gfp_mask & __GFP_WAIT);

        cic = cfq_get_io_context(cfqd, gfp_mask);

        spin_lock_irqsave(q->queue_lock, flags);

        if (!cic)
                goto queue_fail;

new_queue:
        cfqq = cic_to_cfqq(cic, is_sync);
        if (!cfqq || cfqq == &cfqd->oom_cfqq) {
                cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);
                cic_set_cfqq(cic, cfqq, is_sync);
        } else {
                /*
                 * If the queue was seeky for too long, break it apart.
                 */
                if (cfq_cfqq_coop(cfqq) && should_split_cfqq(cfqq)) {
                        cfq_log_cfqq(cfqd, cfqq, "breaking apart cfqq");
                        cfqq = split_cfqq(cic, cfqq);
                        if (!cfqq)
                                goto new_queue;
                }

                /*
                 * Check to see if this queue is scheduled to merge with
                 * another, closely cooperating queue.  The merging of
                 * queues happens here as it must be done in process context.
                 * The reference on new_cfqq was taken in merge_cfqqs.
                 */
                if (cfqq->new_cfqq)
                        cfqq = cfq_merge_cfqqs(cfqd, cic, cfqq);
        }

        cfqq->allocated[rw]++;
        atomic_inc(&cfqq->ref);

        spin_unlock_irqrestore(q->queue_lock, flags);

        rq->elevator_private = cic;
        rq->elevator_private2 = cfqq;
        return 0;

queue_fail:
        if (cic)
                put_io_context(cic->ioc);

        cfq_schedule_dispatch(cfqd);
        spin_unlock_irqrestore(q->queue_lock, flags);
        cfq_log(cfqd, "set_request fail");
        return 1;
}

static void cfq_kick_queue(struct work_struct *work)
{
        struct cfq_data *cfqd =
                container_of(work, struct cfq_data, unplug_work);
        struct request_queue *q = cfqd->queue;

        spin_lock_irq(q->queue_lock);
        __blk_run_queue(cfqd->queue);
        spin_unlock_irq(q->queue_lock);
}

/*
 * Timer running if the active_queue is currently idling inside its time slice
 */
static void cfq_idle_slice_timer(unsigned long data)
{
        struct cfq_data *cfqd = (struct cfq_data *) data;
        struct cfq_queue *cfqq;
        unsigned long flags;
        int timed_out = 1;

        cfq_log(cfqd, "idle timer fired");

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);

        cfqq = cfqd->active_queue;
        if (cfqq) {
                timed_out = 0;

                /*
                 * We saw a request before the queue expired, let it through
                 */
                if (cfq_cfqq_must_dispatch(cfqq))
                        goto out_kick;

                /*
                 * expired
                 */
                if (cfq_slice_used(cfqq))
                        goto expire;

                /*
                 * only expire and reinvoke request handler, if there are
                 * other queues with pending requests
                 */
                if (!cfqd->busy_queues)
                        goto out_cont;

                /*
                 * not expired and it has a request pending, let it dispatch
                 */
                if (!RB_EMPTY_ROOT(&cfqq->sort_list))
                        goto out_kick;
        }
expire:
        cfq_slice_expired(cfqd, timed_out);
out_kick:
        cfq_schedule_dispatch(cfqd);
out_cont:
        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
{
        del_timer_sync(&cfqd->idle_slice_timer);
        cancel_work_sync(&cfqd->unplug_work);
}

static void cfq_put_async_queues(struct cfq_data *cfqd)
{
        int i;

        for (i = 0; i < IOPRIO_BE_NR; i++) {
                if (cfqd->async_cfqq[0][i])
                        cfq_put_queue(cfqd->async_cfqq[0][i]);
                if (cfqd->async_cfqq[1][i])
                        cfq_put_queue(cfqd->async_cfqq[1][i]);
        }

        if (cfqd->async_idle_cfqq)
                cfq_put_queue(cfqd->async_idle_cfqq);
}

static void cfq_exit_queue(struct elevator_queue *e)
{
        struct cfq_data *cfqd = e->elevator_data;
        struct request_queue *q = cfqd->queue;

        cfq_shutdown_timer_wq(cfqd);

        spin_lock_irq(q->queue_lock);

        if (cfqd->active_queue)
                __cfq_slice_expired(cfqd, cfqd->active_queue, 0);

        while (!list_empty(&cfqd->cic_list)) {
                struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
                                                        struct cfq_io_context,
                                                        queue_list);

                __cfq_exit_single_io_context(cfqd, cic);
        }

        cfq_put_async_queues(cfqd);

        spin_unlock_irq(q->queue_lock);

        cfq_shutdown_timer_wq(cfqd);

        kfree(cfqd);
}

static void *cfq_init_queue(struct request_queue *q)
{
        struct cfq_data *cfqd;
        int i;

        cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
        if (!cfqd)
                return NULL;

        for (i = 0; i < 2; ++i)
                cfqd->service_trees[i] = CFQ_RB_ROOT;
        cfqd->service_tree_idle = CFQ_RB_ROOT;

        /*
         * Not strictly needed (since RB_ROOT just clears the node and we
         * zeroed cfqd on alloc), but better be safe in case someone decides
         * to add magic to the rb code
         */
        for (i = 0; i < CFQ_PRIO_LISTS; i++)
                cfqd->prio_trees[i] = RB_ROOT;

        /*
         * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
         * Grab a permanent reference to it, so that the normal code flow
         * will not attempt to free it.
         */
        cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
        atomic_inc(&cfqd->oom_cfqq.ref);

        INIT_LIST_HEAD(&cfqd->cic_list);

        cfqd->queue = q;

        init_timer(&cfqd->idle_slice_timer);
        cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
        cfqd->idle_slice_timer.data = (unsigned long) cfqd;

        INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);

        cfqd->cfq_quantum = cfq_quantum;
        cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
        cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
        cfqd->cfq_back_max = cfq_back_max;
        cfqd->cfq_back_penalty = cfq_back_penalty;
        cfqd->cfq_slice[0] = cfq_slice_async;
        cfqd->cfq_slice[1] = cfq_slice_sync;
        cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
        cfqd->cfq_slice_idle = cfq_slice_idle;
        cfqd->cfq_latency = 1;
        cfqd->hw_tag = 1;
        cfqd->last_end_sync_rq = jiffies;
        return cfqd;
}

static void cfq_slab_kill(void)
{
        /*
         * Caller already ensured that pending RCU callbacks are completed,
         * so we should have no busy allocations at this point.
         */
        if (cfq_pool)
                kmem_cache_destroy(cfq_pool);
        if (cfq_ioc_pool)
                kmem_cache_destroy(cfq_ioc_pool);
}

static int __init cfq_slab_setup(void)
{
        cfq_pool = KMEM_CACHE(cfq_queue, 0);
        if (!cfq_pool)
                goto fail;

        cfq_ioc_pool = KMEM_CACHE(cfq_io_context, 0);
        if (!cfq_ioc_pool)
                goto fail;

        return 0;
fail:
        cfq_slab_kill();
        return -ENOMEM;
}

/*
 * sysfs parts below -->
 */
static ssize_t
cfq_var_show(unsigned int var, char *page)
{
        return sprintf(page, "%d\n", var);
}

static ssize_t
cfq_var_store(unsigned int *var, const char *page, size_t count)
{
        char *p = (char *) page;

        *var = simple_strtoul(p, &p, 10);
        return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
{                                                                       \
        struct cfq_data *cfqd = e->elevator_data;                       \
        unsigned int __data = __VAR;                                    \
        if (__CONV)                                                     \
                __data = jiffies_to_msecs(__data);                      \
        return cfq_var_show(__data, (page));                            \
}
SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
SHOW_FUNCTION(cfq_back_seek_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_seek_penalty_show, cfqd->cfq_back_penalty, 0);
SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
SHOW_FUNCTION(cfq_low_latency_show, cfqd->cfq_latency, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
{                                                                       \
        struct cfq_data *cfqd = e->elevator_data;                       \
        unsigned int __data;                                            \
        int ret = cfq_var_store(&__data, (page), count);                \
        if (__data < (MIN))                                             \
                __data = (MIN);                                         \
        else if (__data > (MAX))                                        \
                __data = (MAX);                                         \
        if (__CONV)                                                     \
                *(__PTR) = msecs_to_jiffies(__data);                    \
        else                                                            \
                *(__PTR) = __data;                                      \
        return ret;                                                     \
}
STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1,
                UINT_MAX, 1);
STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1,
                UINT_MAX, 1);
STORE_FUNCTION(cfq_back_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
STORE_FUNCTION(cfq_back_seek_penalty_store, &cfqd->cfq_back_penalty, 1,
                UINT_MAX, 0);
STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
                UINT_MAX, 0);
STORE_FUNCTION(cfq_low_latency_store, &cfqd->cfq_latency, 0, 1, 0);
#undef STORE_FUNCTION

#define CFQ_ATTR(name) \
        __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)

static struct elv_fs_entry cfq_attrs[] = {
        CFQ_ATTR(quantum),
        CFQ_ATTR(fifo_expire_sync),
        CFQ_ATTR(fifo_expire_async),
        CFQ_ATTR(back_seek_max),
        CFQ_ATTR(back_seek_penalty),
        CFQ_ATTR(slice_sync),
        CFQ_ATTR(slice_async),
        CFQ_ATTR(slice_async_rq),
        CFQ_ATTR(slice_idle),
        CFQ_ATTR(low_latency),
        __ATTR_NULL
};

static struct elevator_type iosched_cfq = {
        .ops = {
                .elevator_merge_fn =            cfq_merge,
                .elevator_merged_fn =           cfq_merged_request,
                .elevator_merge_req_fn =        cfq_merged_requests,
                .elevator_allow_merge_fn =      cfq_allow_merge,
                .elevator_dispatch_fn =         cfq_dispatch_requests,
                .elevator_add_req_fn =          cfq_insert_request,
                .elevator_activate_req_fn =     cfq_activate_request,
                .elevator_deactivate_req_fn =   cfq_deactivate_request,
                .elevator_queue_empty_fn =      cfq_queue_empty,
                .elevator_completed_req_fn =    cfq_completed_request,
                .elevator_former_req_fn =       elv_rb_former_request,
                .elevator_latter_req_fn =       elv_rb_latter_request,
                .elevator_set_req_fn =          cfq_set_request,
                .elevator_put_req_fn =          cfq_put_request,
                .elevator_may_queue_fn =        cfq_may_queue,
                .elevator_init_fn =             cfq_init_queue,
                .elevator_exit_fn =             cfq_exit_queue,
                .trim =                         cfq_free_io_context,
        },
        .elevator_attrs =       cfq_attrs,
        .elevator_name =        "cfq",
        .elevator_owner =       THIS_MODULE,
};

static int __init cfq_init(void)
{
        /*
         * could be 0 on HZ < 1000 setups
         */
        if (!cfq_slice_async)
                cfq_slice_async = 1;
        if (!cfq_slice_idle)
                cfq_slice_idle = 1;

        if (cfq_slab_setup())
                return -ENOMEM;

        elv_register(&iosched_cfq);

        return 0;
}

static void __exit cfq_exit(void)
{
        DECLARE_COMPLETION_ONSTACK(all_gone);
        elv_unregister(&iosched_cfq);
        ioc_gone = &all_gone;
        /* ioc_gone's update must be visible before reading ioc_count */
        smp_wmb();

        /*
         * this also protects us from entering cfq_slab_kill() with
         * pending RCU callbacks
         */
        if (elv_ioc_count_read(cfq_ioc_count))
                wait_for_completion(&all_gone);
        cfq_slab_kill();
}

module_init(cfq_init);
module_exit(cfq_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");