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Diffstat (limited to 'block/as-iosched.c')
| -rw-r--r-- | block/as-iosched.c | 1985 |
1 files changed, 1985 insertions, 0 deletions
diff --git a/block/as-iosched.c b/block/as-iosched.c new file mode 100644 index 00000000000..c6744ff3829 --- /dev/null +++ b/block/as-iosched.c @@ -0,0 +1,1985 @@ +/* + * linux/drivers/block/as-iosched.c + * + * Anticipatory & deadline i/o scheduler. + * + * Copyright (C) 2002 Jens Axboe <axboe@suse.de> + * Nick Piggin <piggin@cyberone.com.au> + * + */ +#include <linux/kernel.h> +#include <linux/fs.h> +#include <linux/blkdev.h> +#include <linux/elevator.h> +#include <linux/bio.h> +#include <linux/config.h> +#include <linux/module.h> +#include <linux/slab.h> +#include <linux/init.h> +#include <linux/compiler.h> +#include <linux/hash.h> +#include <linux/rbtree.h> +#include <linux/interrupt.h> + +#define REQ_SYNC 1 +#define REQ_ASYNC 0 + +/* + * See Documentation/block/as-iosched.txt + */ + +/* + * max time before a read is submitted. + */ +#define default_read_expire (HZ / 8) + +/* + * ditto for writes, these limits are not hard, even + * if the disk is capable of satisfying them. + */ +#define default_write_expire (HZ / 4) + +/* + * read_batch_expire describes how long we will allow a stream of reads to + * persist before looking to see whether it is time to switch over to writes. + */ +#define default_read_batch_expire (HZ / 2) + +/* + * write_batch_expire describes how long we want a stream of writes to run for. + * This is not a hard limit, but a target we set for the auto-tuning thingy. + * See, the problem is: we can send a lot of writes to disk cache / TCQ in + * a short amount of time... + */ +#define default_write_batch_expire (HZ / 8) + +/* + * max time we may wait to anticipate a read (default around 6ms) + */ +#define default_antic_expire ((HZ / 150) ? HZ / 150 : 1) + +/* + * Keep track of up to 20ms thinktimes. We can go as big as we like here, + * however huge values tend to interfere and not decay fast enough. A program + * might be in a non-io phase of operation. Waiting on user input for example, + * or doing a lengthy computation. A small penalty can be justified there, and + * will still catch out those processes that constantly have large thinktimes. + */ +#define MAX_THINKTIME (HZ/50UL) + +/* Bits in as_io_context.state */ +enum as_io_states { + AS_TASK_RUNNING=0, /* Process has not exitted */ + AS_TASK_IOSTARTED, /* Process has started some IO */ + AS_TASK_IORUNNING, /* Process has completed some IO */ +}; + +enum anticipation_status { + ANTIC_OFF=0, /* Not anticipating (normal operation) */ + ANTIC_WAIT_REQ, /* The last read has not yet completed */ + ANTIC_WAIT_NEXT, /* Currently anticipating a request vs + last read (which has completed) */ + ANTIC_FINISHED, /* Anticipating but have found a candidate + * or timed out */ +}; + +struct as_data { + /* + * run time data + */ + + struct request_queue *q; /* the "owner" queue */ + + /* + * requests (as_rq s) are present on both sort_list and fifo_list + */ + struct rb_root sort_list[2]; + struct list_head fifo_list[2]; + + struct as_rq *next_arq[2]; /* next in sort order */ + sector_t last_sector[2]; /* last REQ_SYNC & REQ_ASYNC sectors */ + struct list_head *hash; /* request hash */ + + unsigned long exit_prob; /* probability a task will exit while + being waited on */ + unsigned long new_ttime_total; /* mean thinktime on new proc */ + unsigned long new_ttime_mean; + u64 new_seek_total; /* mean seek on new proc */ + sector_t new_seek_mean; + + unsigned long current_batch_expires; + unsigned long last_check_fifo[2]; + int changed_batch; /* 1: waiting for old batch to end */ + int new_batch; /* 1: waiting on first read complete */ + int batch_data_dir; /* current batch REQ_SYNC / REQ_ASYNC */ + int write_batch_count; /* max # of reqs in a write batch */ + int current_write_count; /* how many requests left this batch */ + int write_batch_idled; /* has the write batch gone idle? */ + mempool_t *arq_pool; + + enum anticipation_status antic_status; + unsigned long antic_start; /* jiffies: when it started */ + struct timer_list antic_timer; /* anticipatory scheduling timer */ + struct work_struct antic_work; /* Deferred unplugging */ + struct io_context *io_context; /* Identify the expected process */ + int ioc_finished; /* IO associated with io_context is finished */ + int nr_dispatched; + + /* + * settings that change how the i/o scheduler behaves + */ + unsigned long fifo_expire[2]; + unsigned long batch_expire[2]; + unsigned long antic_expire; +}; + +#define list_entry_fifo(ptr) list_entry((ptr), struct as_rq, fifo) + +/* + * per-request data. + */ +enum arq_state { + AS_RQ_NEW=0, /* New - not referenced and not on any lists */ + AS_RQ_QUEUED, /* In the request queue. It belongs to the + scheduler */ + AS_RQ_DISPATCHED, /* On the dispatch list. It belongs to the + driver now */ + AS_RQ_PRESCHED, /* Debug poisoning for requests being used */ + AS_RQ_REMOVED, + AS_RQ_MERGED, + AS_RQ_POSTSCHED, /* when they shouldn't be */ +}; + +struct as_rq { + /* + * rbtree index, key is the starting offset + */ + struct rb_node rb_node; + sector_t rb_key; + + struct request *request; + + struct io_context *io_context; /* The submitting task */ + + /* + * request hash, key is the ending offset (for back merge lookup) + */ + struct list_head hash; + unsigned int on_hash; + + /* + * expire fifo + */ + struct list_head fifo; + unsigned long expires; + + unsigned int is_sync; + enum arq_state state; +}; + +#define RQ_DATA(rq) ((struct as_rq *) (rq)->elevator_private) + +static kmem_cache_t *arq_pool; + +/* + * IO Context helper functions + */ + +/* Called to deallocate the as_io_context */ +static void free_as_io_context(struct as_io_context *aic) +{ + kfree(aic); +} + +/* Called when the task exits */ +static void exit_as_io_context(struct as_io_context *aic) +{ + WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state)); + clear_bit(AS_TASK_RUNNING, &aic->state); +} + +static struct as_io_context *alloc_as_io_context(void) +{ + struct as_io_context *ret; + + ret = kmalloc(sizeof(*ret), GFP_ATOMIC); + if (ret) { + ret->dtor = free_as_io_context; + ret->exit = exit_as_io_context; + ret->state = 1 << AS_TASK_RUNNING; + atomic_set(&ret->nr_queued, 0); + atomic_set(&ret->nr_dispatched, 0); + spin_lock_init(&ret->lock); + ret->ttime_total = 0; + ret->ttime_samples = 0; + ret->ttime_mean = 0; + ret->seek_total = 0; + ret->seek_samples = 0; + ret->seek_mean = 0; + } + + return ret; +} + +/* + * If the current task has no AS IO context then create one and initialise it. + * Then take a ref on the task's io context and return it. + */ +static struct io_context *as_get_io_context(void) +{ + struct io_context *ioc = get_io_context(GFP_ATOMIC); + if (ioc && !ioc->aic) { + ioc->aic = alloc_as_io_context(); + if (!ioc->aic) { + put_io_context(ioc); + ioc = NULL; + } + } + return ioc; +} + +static void as_put_io_context(struct as_rq *arq) +{ + struct as_io_context *aic; + + if (unlikely(!arq->io_context)) + return; + + aic = arq->io_context->aic; + + if (arq->is_sync == REQ_SYNC && aic) { + spin_lock(&aic->lock); + set_bit(AS_TASK_IORUNNING, &aic->state); + aic->last_end_request = jiffies; + spin_unlock(&aic->lock); + } + + put_io_context(arq->io_context); +} + +/* + * the back merge hash support functions + */ +static const int as_hash_shift = 6; +#define AS_HASH_BLOCK(sec) ((sec) >> 3) +#define AS_HASH_FN(sec) (hash_long(AS_HASH_BLOCK((sec)), as_hash_shift)) +#define AS_HASH_ENTRIES (1 << as_hash_shift) +#define rq_hash_key(rq) ((rq)->sector + (rq)->nr_sectors) +#define list_entry_hash(ptr) list_entry((ptr), struct as_rq, hash) + +static inline void __as_del_arq_hash(struct as_rq *arq) +{ + arq->on_hash = 0; + list_del_init(&arq->hash); +} + +static inline void as_del_arq_hash(struct as_rq *arq) +{ + if (arq->on_hash) + __as_del_arq_hash(arq); +} + +static void as_add_arq_hash(struct as_data *ad, struct as_rq *arq) +{ + struct request *rq = arq->request; + + BUG_ON(arq->on_hash); + + arq->on_hash = 1; + list_add(&arq->hash, &ad->hash[AS_HASH_FN(rq_hash_key(rq))]); +} + +/* + * move hot entry to front of chain + */ +static inline void as_hot_arq_hash(struct as_data *ad, struct as_rq *arq) +{ + struct request *rq = arq->request; + struct list_head *head = &ad->hash[AS_HASH_FN(rq_hash_key(rq))]; + + if (!arq->on_hash) { + WARN_ON(1); + return; + } + + if (arq->hash.prev != head) { + list_del(&arq->hash); + list_add(&arq->hash, head); + } +} + +static struct request *as_find_arq_hash(struct as_data *ad, sector_t offset) +{ + struct list_head *hash_list = &ad->hash[AS_HASH_FN(offset)]; + struct list_head *entry, *next = hash_list->next; + + while ((entry = next) != hash_list) { + struct as_rq *arq = list_entry_hash(entry); + struct request *__rq = arq->request; + + next = entry->next; + + BUG_ON(!arq->on_hash); + + if (!rq_mergeable(__rq)) { + as_del_arq_hash(arq); + continue; + } + + if (rq_hash_key(__rq) == offset) + return __rq; + } + + return NULL; +} + +/* + * rb tree support functions + */ +#define RB_NONE (2) +#define RB_EMPTY(root) ((root)->rb_node == NULL) +#define ON_RB(node) ((node)->rb_color != RB_NONE) +#define RB_CLEAR(node) ((node)->rb_color = RB_NONE) +#define rb_entry_arq(node) rb_entry((node), struct as_rq, rb_node) +#define ARQ_RB_ROOT(ad, arq) (&(ad)->sort_list[(arq)->is_sync]) +#define rq_rb_key(rq) (rq)->sector + +/* + * as_find_first_arq finds the first (lowest sector numbered) request + * for the specified data_dir. Used to sweep back to the start of the disk + * (1-way elevator) after we process the last (highest sector) request. + */ +static struct as_rq *as_find_first_arq(struct as_data *ad, int data_dir) +{ + struct rb_node *n = ad->sort_list[data_dir].rb_node; + + if (n == NULL) + return NULL; + + for (;;) { + if (n->rb_left == NULL) + return rb_entry_arq(n); + + n = n->rb_left; + } +} + +/* + * Add the request to the rb tree if it is unique. If there is an alias (an + * existing request against the same sector), which can happen when using + * direct IO, then return the alias. + */ +static struct as_rq *as_add_arq_rb(struct as_data *ad, struct as_rq *arq) +{ + struct rb_node **p = &ARQ_RB_ROOT(ad, arq)->rb_node; + struct rb_node *parent = NULL; + struct as_rq *__arq; + struct request *rq = arq->request; + + arq->rb_key = rq_rb_key(rq); + + while (*p) { + parent = *p; + __arq = rb_entry_arq(parent); + + if (arq->rb_key < __arq->rb_key) + p = &(*p)->rb_left; + else if (arq->rb_key > __arq->rb_key) + p = &(*p)->rb_right; + else + return __arq; + } + + rb_link_node(&arq->rb_node, parent, p); + rb_insert_color(&arq->rb_node, ARQ_RB_ROOT(ad, arq)); + + return NULL; +} + +static inline void as_del_arq_rb(struct as_data *ad, struct as_rq *arq) +{ + if (!ON_RB(&arq->rb_node)) { + WARN_ON(1); + return; + } + + rb_erase(&arq->rb_node, ARQ_RB_ROOT(ad, arq)); + RB_CLEAR(&arq->rb_node); +} + +static struct request * +as_find_arq_rb(struct as_data *ad, sector_t sector, int data_dir) +{ + struct rb_node *n = ad->sort_list[data_dir].rb_node; + struct as_rq *arq; + + while (n) { + arq = rb_entry_arq(n); + + if (sector < arq->rb_key) + n = n->rb_left; + else if (sector > arq->rb_key) + n = n->rb_right; + else + return arq->request; + } + + return NULL; +} + +/* + * IO Scheduler proper + */ + +#define MAXBACK (1024 * 1024) /* + * Maximum distance the disk will go backward + * for a request. + */ + +#define BACK_PENALTY 2 + +/* + * as_choose_req selects the preferred one of two requests of the same data_dir + * ignoring time - eg. timeouts, which is the job of as_dispatch_request + */ +static struct as_rq * +as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2) +{ + int data_dir; + sector_t last, s1, s2, d1, d2; + int r1_wrap=0, r2_wrap=0; /* requests are behind the disk head */ + const sector_t maxback = MAXBACK; + + if (arq1 == NULL || arq1 == arq2) + return arq2; + if (arq2 == NULL) + return arq1; + + data_dir = arq1->is_sync; + + last = ad->last_sector[data_dir]; + s1 = arq1->request->sector; + s2 = arq2->request->sector; + + BUG_ON(data_dir != arq2->is_sync); + + /* + * 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+maxback >= last) + d1 = (last - s1)*BACK_PENALTY; + else { + r1_wrap = 1; + d1 = 0; /* shut up, gcc */ + } + + if (s2 >= last) + d2 = s2 - last; + else if (s2+maxback >= last) + d2 = (last - s2)*BACK_PENALTY; + else { + r2_wrap = 1; + d2 = 0; + } + + /* Found required data */ + if (!r1_wrap && r2_wrap) + return arq1; + else if (!r2_wrap && r1_wrap) + return arq2; + else if (r1_wrap && r2_wrap) { + /* both behind the head */ + if (s1 <= s2) + return arq1; + else + return arq2; + } + + /* Both requests in front of the head */ + if (d1 < d2) + return arq1; + else if (d2 < d1) + return arq2; + else { + if (s1 >= s2) + return arq1; + else + return arq2; + } +} + +/* + * as_find_next_arq finds the next request after @prev in elevator order. + * this with as_choose_req form the basis for how the scheduler chooses + * what request to process next. Anticipation works on top of this. + */ +static struct as_rq *as_find_next_arq(struct as_data *ad, struct as_rq *last) +{ + const int data_dir = last->is_sync; + struct as_rq *ret; + struct rb_node *rbnext = rb_next(&last->rb_node); + struct rb_node *rbprev = rb_prev(&last->rb_node); + struct as_rq *arq_next, *arq_prev; + + BUG_ON(!ON_RB(&last->rb_node)); + + if (rbprev) + arq_prev = rb_entry_arq(rbprev); + else + arq_prev = NULL; + + if (rbnext) + arq_next = rb_entry_arq(rbnext); + else { + arq_next = as_find_first_arq(ad, data_dir); + if (arq_next == last) + arq_next = NULL; + } + + ret = as_choose_req(ad, arq_next, arq_prev); + + return ret; +} + +/* + * anticipatory scheduling functions follow + */ + +/* + * as_antic_expired tells us when we have anticipated too long. + * The funny "absolute difference" math on the elapsed time is to handle + * jiffy wraps, and disks which have been idle for 0x80000000 jiffies. + */ +static int as_antic_expired(struct as_data *ad) +{ + long delta_jif; + + delta_jif = jiffies - ad->antic_start; + if (unlikely(delta_jif < 0)) + delta_jif = -delta_jif; + if (delta_jif < ad->antic_expire) + return 0; + + return 1; +} + +/* + * as_antic_waitnext starts anticipating that a nice request will soon be + * submitted. See also as_antic_waitreq + */ +static void as_antic_waitnext(struct as_data *ad) +{ + unsigned long timeout; + + BUG_ON(ad->antic_status != ANTIC_OFF + && ad->antic_status != ANTIC_WAIT_REQ); + + timeout = ad->antic_start + ad->antic_expire; + + mod_timer(&ad->antic_timer, timeout); + + ad->antic_status = ANTIC_WAIT_NEXT; +} + +/* + * as_antic_waitreq starts anticipating. We don't start timing the anticipation + * until the request that we're anticipating on has finished. This means we + * are timing from when the candidate process wakes up hopefully. + */ +static void as_antic_waitreq(struct as_data *ad) +{ + BUG_ON(ad->antic_status == ANTIC_FINISHED); + if (ad->antic_status == ANTIC_OFF) { + if (!ad->io_context || ad->ioc_finished) + as_antic_waitnext(ad); + else + ad->antic_status = ANTIC_WAIT_REQ; + } +} + +/* + * This is called directly by the functions in this file to stop anticipation. + * We kill the timer and schedule a call to the request_fn asap. + */ +static void as_antic_stop(struct as_data *ad) +{ + int status = ad->antic_status; + + if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) { + if (status == ANTIC_WAIT_NEXT) + del_timer(&ad->antic_timer); + ad->antic_status = ANTIC_FINISHED; + /* see as_work_handler */ + kblockd_schedule_work(&ad->antic_work); + } +} + +/* + * as_antic_timeout is the timer function set by as_antic_waitnext. + */ +static void as_antic_timeout(unsigned long data) +{ + struct request_queue *q = (struct request_queue *)data; + struct as_data *ad = q->elevator->elevator_data; + unsigned long flags; + + spin_lock_irqsave(q->queue_lock, flags); + if (ad->antic_status == ANTIC_WAIT_REQ + || ad->antic_status == ANTIC_WAIT_NEXT) { + struct as_io_context *aic = ad->io_context->aic; + + ad->antic_status = ANTIC_FINISHED; + kblockd_schedule_work(&ad->antic_work); + + if (aic->ttime_samples == 0) { + /* process anticipated on has exitted or timed out*/ + ad->exit_prob = (7*ad->exit_prob + 256)/8; + } + } + spin_unlock_irqrestore(q->queue_lock, flags); +} + +/* + * as_close_req decides if one request is considered "close" to the + * previous one issued. + */ +static int as_close_req(struct as_data *ad, struct as_rq *arq) +{ + unsigned long delay; /* milliseconds */ + sector_t last = ad->last_sector[ad->batch_data_dir]; + sector_t next = arq->request->sector; + sector_t delta; /* acceptable close offset (in sectors) */ + + if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished) + delay = 0; + else + delay = ((jiffies - ad->antic_start) * 1000) / HZ; + + if (delay <= 1) + delta = 64; + else if (delay <= 20 && delay <= ad->antic_expire) + delta = 64 << (delay-1); + else + return 1; + + return (last - (delta>>1) <= next) && (next <= last + delta); +} + +/* + * as_can_break_anticipation returns true if we have been anticipating this + * request. + * + * It also returns true if the process against which we are anticipating + * submits a write - that's presumably an fsync, O_SYNC write, etc. We want to + * dispatch it ASAP, because we know that application will not be submitting + * any new reads. + * + * If the task which has submitted the request has exitted, break anticipation. + * + * If this task has queued some other IO, do not enter enticipation. + */ +static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq) +{ + struct io_context *ioc; + struct as_io_context *aic; + sector_t s; + + ioc = ad->io_context; + BUG_ON(!ioc); + + if (arq && ioc == arq->io_context) { + /* request from same process */ + return 1; + } + + if (ad->ioc_finished && as_antic_expired(ad)) { + /* + * In this situation status should really be FINISHED, + * however the timer hasn't had the chance to run yet. + */ + return 1; + } + + aic = ioc->aic; + if (!aic) + return 0; + + if (!test_bit(AS_TASK_RUNNING, &aic->state)) { + /* process anticipated on has exitted */ + if (aic->ttime_samples == 0) + ad->exit_prob = (7*ad->exit_prob + 256)/8; + return 1; + } + + if (atomic_read(&aic->nr_queued) > 0) { + /* process has more requests queued */ + return 1; + } + + if (atomic_read(&aic->nr_dispatched) > 0) { + /* process has more requests dispatched */ + return 1; + } + + if (arq && arq->is_sync == REQ_SYNC && as_close_req(ad, arq)) { + /* + * Found a close request that is not one of ours. + * + * This makes close requests from another process reset + * our thinktime delay. Is generally useful when there are + * two or more cooperating processes working in the same + * area. + */ + spin_lock(&aic->lock); + aic->last_end_request = jiffies; + spin_unlock(&aic->lock); + return 1; + } + + + if (aic->ttime_samples == 0) { + if (ad->new_ttime_mean > ad->antic_expire) + return 1; + if (ad->exit_prob > 128) + return 1; + } else if (aic->ttime_mean > ad->antic_expire) { + /* the process thinks too much between requests */ + return 1; + } + + if (!arq) + return 0; + + if (ad->last_sector[REQ_SYNC] < arq->request->sector) + s = arq->request->sector - ad->last_sector[REQ_SYNC]; + else + s = ad->last_sector[REQ_SYNC] - arq->request->sector; + + if (aic->seek_samples == 0) { + /* + * Process has just started IO. Use past statistics to + * guage success possibility + */ + if (ad->new_seek_mean > s) { + /* this request is better than what we're expecting */ + return 1; + } + + } else { + if (aic->seek_mean > s) { + /* this request is better than what we're expecting */ + return 1; + } + } + + return 0; +} + +/* + * as_can_anticipate indicates weather we should either run arq + * or keep anticipating a better request. + */ +static int as_can_anticipate(struct as_data *ad, struct as_rq *arq) +{ + if (!ad->io_context) + /* + * Last request submitted was a write + */ + return 0; + + if (ad->antic_status == ANTIC_FINISHED) + /* + * Don't restart if we have just finished. Run the next request + */ + return 0; + + if (as_can_break_anticipation(ad, arq)) + /* + * This request is a good candidate. Don't keep anticipating, + * run it. + */ + return 0; + + /* + * OK from here, we haven't finished, and don't have a decent request! + * Status is either ANTIC_OFF so start waiting, + * ANTIC_WAIT_REQ so continue waiting for request to finish + * or ANTIC_WAIT_NEXT so continue waiting for an acceptable request. + * + */ + + return 1; +} + +static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic, unsigned long ttime) +{ + /* fixed point: 1.0 == 1<<8 */ + if (aic->ttime_samples == 0) { + ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8; + ad->new_ttime_mean = ad->new_ttime_total / 256; + + ad->exit_prob = (7*ad->exit_prob)/8; + } + aic->ttime_samples = (7*aic->ttime_samples + 256) / 8; + aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8; + aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples; +} + +static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic, sector_t sdist) +{ + u64 total; + + if (aic->seek_samples == 0) { + ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8; + ad->new_seek_mean = ad->new_seek_total / 256; + } + + /* + * Don't allow the seek distance to get too large from the + * odd fragment, pagein, etc + */ + if (aic->seek_samples <= 60) /* second&third seek */ + sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024); + else + sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64); + + aic->seek_samples = (7*aic->seek_samples + 256) / 8; + aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8; + total = aic->seek_total + (aic->seek_samples/2); + do_div(total, aic->seek_samples); + aic->seek_mean = (sector_t)total; +} + +/* + * as_update_iohist keeps a decaying histogram of IO thinktimes, and + * updates @aic->ttime_mean based on that. It is called when a new + * request is queued. + */ +static void as_update_iohist(struct as_data *ad, struct as_io_context *aic, struct request *rq) +{ + struct as_rq *arq = RQ_DATA(rq); + int data_dir = arq->is_sync; + unsigned long thinktime; + sector_t seek_dist; + + if (aic == NULL) + return; + + if (data_dir == REQ_SYNC) { + unsigned long in_flight = atomic_read(&aic->nr_queued) + + atomic_read(&aic->nr_dispatched); + spin_lock(&aic->lock); + if (test_bit(AS_TASK_IORUNNING, &aic->state) || + test_bit(AS_TASK_IOSTARTED, &aic->state)) { + /* Calculate read -> read thinktime */ + if (test_bit(AS_TASK_IORUNNING, &aic->state) + && in_flight == 0) { + thinktime = jiffies - aic->last_end_request; + thinktime = min(thinktime, MAX_THINKTIME-1); + } else + thinktime = 0; + as_update_thinktime(ad, aic, thinktime); + + /* Calculate read -> read seek distance */ + if (aic->last_request_pos < rq->sector) + seek_dist = rq->sector - aic->last_request_pos; + else + seek_dist = aic->last_request_pos - rq->sector; + as_update_seekdist(ad, aic, seek_dist); + } + aic->last_request_pos = rq->sector + rq->nr_sectors; + set_bit(AS_TASK_IOSTARTED, &aic->state); + spin_unlock(&aic->lock); + } +} + +/* + * as_update_arq must be called whenever a request (arq) is added to + * the sort_list. This function keeps caches up to date, and checks if the + * request might be one we are "anticipating" + */ +static void as_update_arq(struct as_data *ad, struct as_rq *arq) +{ + const int data_dir = arq->is_sync; + + /* keep the next_arq cache up to date */ + ad->next_arq[data_dir] = as_choose_req(ad, arq, ad->next_arq[data_dir]); + + /* + * have we been anticipating this request? + * or does it come from the same process as the one we are anticipating + * for? + */ + if (ad->antic_status == ANTIC_WAIT_REQ + || ad->antic_status == ANTIC_WAIT_NEXT) { + if (as_can_break_anticipation(ad, arq)) + as_antic_stop(ad); + } +} + +/* + * Gathers timings and resizes the write batch automatically + */ +static void update_write_batch(struct as_data *ad) +{ + unsigned long batch = ad->batch_expire[REQ_ASYNC]; + long write_time; + + write_time = (jiffies - ad->current_batch_expires) + batch; + if (write_time < 0) + write_time = 0; + + if (write_time > batch && !ad->write_batch_idled) { + if (write_time > batch * 3) + ad->write_batch_count /= 2; + else + ad->write_batch_count--; + } else if (write_time < batch && ad->current_write_count == 0) { + if (batch > write_time * 3) + ad->write_batch_count *= 2; + else + ad->write_batch_count++; + } + + if (ad->write_batch_count < 1) + ad->write_batch_count = 1; +} + +/* + * as_completed_request is to be called when a request has completed and + * returned something to the requesting process, be it an error or data. + */ +static void as_completed_request(request_queue_t *q, struct request *rq) +{ + struct as_data *ad = q->elevator->elevator_data; + struct as_rq *arq = RQ_DATA(rq); + + WARN_ON(!list_empty(&rq->queuelist)); + + if (arq->state != AS_RQ_REMOVED) { + printk("arq->state %d\n", arq->state); + WARN_ON(1); + goto out; + } + + if (ad->changed_batch && ad->nr_dispatched == 1) { + kblockd_schedule_work(&ad->antic_work); + ad->changed_batch = 0; + + if (ad->batch_data_dir == REQ_SYNC) + ad->new_batch = 1; + } + WARN_ON(ad->nr_dispatched == 0); + ad->nr_dispatched--; + + /* + * Start counting the batch from when a request of that direction is + * actually serviced. This should help devices with big TCQ windows + * and writeback caches + */ + if (ad->new_batch && ad->batch_data_dir == arq->is_sync) { + update_write_batch(ad); + ad->current_batch_expires = jiffies + + ad->batch_expire[REQ_SYNC]; + ad->new_batch = 0; + } + + if (ad->io_context == arq->io_context && ad->io_context) { + ad->antic_start = jiffies; + ad->ioc_finished = 1; + if (ad->antic_status == ANTIC_WAIT_REQ) { + /* + * We were waiting on this request, now anticipate + * the next one + */ + as_antic_waitnext(ad); + } + } + + as_put_io_context(arq); +out: + arq->state = AS_RQ_POSTSCHED; +} + +/* + * as_remove_queued_request removes a request from the pre dispatch queue + * without updating refcounts. It is expected the caller will drop the + * reference unless it replaces the request at somepart of the elevator + * (ie. the dispatch queue) + */ +static void as_remove_queued_request(request_queue_t *q, struct request *rq) +{ + struct as_rq *arq = RQ_DATA(rq); + const int data_dir = arq->is_sync; + struct as_data *ad = q->elevator->elevator_data; + + WARN_ON(arq->state != AS_RQ_QUEUED); + + if (arq->io_context && arq->io_context->aic) { + BUG_ON(!atomic_read(&arq->io_context->aic->nr_queued)); + atomic_dec(&arq->io_context->aic->nr_queued); + } + + /* + * Update the "next_arq" cache if we are about to remove its + * entry + */ + if (ad->next_arq[data_dir] == arq) + ad->next_arq[data_dir] = as_find_next_arq(ad, arq); + + list_del_init(&arq->fifo); + as_del_arq_hash(arq); + as_del_arq_rb(ad, arq); +} + +/* + * as_fifo_expired returns 0 if there are no expired reads on the fifo, + * 1 otherwise. It is ratelimited so that we only perform the check once per + * `fifo_expire' interval. Otherwise a large number of expired requests + * would create a hopeless seekstorm. + * + * See as_antic_expired comment. + */ +static int as_fifo_expired(struct as_data *ad, int adir) +{ + struct as_rq *arq; + long delta_jif; + + delta_jif = jiffies - ad->last_check_fifo[adir]; + if (unlikely(delta_jif < 0)) + delta_jif = -delta_jif; + if (delta_jif < ad->fifo_expire[adir]) + return 0; + + ad->last_check_fifo[adir] = jiffies; + + if (list_empty(&ad->fifo_list[adir])) + return 0; + + arq = list_entry_fifo(ad->fifo_list[adir].next); + + return time_after(jiffies, arq->expires); +} + +/* + * as_batch_expired returns true if the current batch has expired. A batch + * is a set of reads or a set of writes. + */ +static inline int as_batch_expired(struct as_data *ad) +{ + if (ad->changed_batch || ad->new_batch) + return 0; + + if (ad->batch_data_dir == REQ_SYNC) + /* TODO! add a check so a complete fifo gets written? */ + return time_after(jiffies, ad->current_batch_expires); + + return time_after(jiffies, ad->current_batch_expires) + || ad->current_write_count == 0; +} + +/* + * move an entry to dispatch queue + */ +static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq) +{ + struct request *rq = arq->request; + const int data_dir = arq->is_sync; + + BUG_ON(!ON_RB(&arq->rb_node)); + + as_antic_stop(ad); + ad->antic_status = ANTIC_OFF; + + /* + * This has to be set in order to be correctly updated by + * as_find_next_arq + */ + ad->last_sector[data_dir] = rq->sector + rq->nr_sectors; + + if (data_dir == REQ_SYNC) { + /* In case we have to anticipate after this */ + copy_io_context(&ad->io_context, &arq->io_context); + } else { + if (ad->io_context) { + put_io_context(ad->io_context); + ad->io_context = NULL; + } + + if (ad->current_write_count != 0) + ad->current_write_count--; + } + ad->ioc_finished = 0; + + ad->next_arq[data_dir] = as_find_next_arq(ad, arq); + + /* + * take it off the sort and fifo list, add to dispatch queue + */ + while (!list_empty(&rq->queuelist)) { + struct request *__rq = list_entry_rq(rq->queuelist.next); + struct as_rq *__arq = RQ_DATA(__rq); + + list_del(&__rq->queuelist); + + elv_dispatch_add_tail(ad->q, __rq); + + if (__arq->io_context && __arq->io_context->aic) + atomic_inc(&__arq->io_context->aic->nr_dispatched); + + WARN_ON(__arq->state != AS_RQ_QUEUED); + __arq->state = AS_RQ_DISPATCHED; + + ad->nr_dispatched++; + } + + as_remove_queued_request(ad->q, rq); + WARN_ON(arq->state != AS_RQ_QUEUED); + + elv_dispatch_sort(ad->q, rq); + + arq->state = AS_RQ_DISPATCHED; + if (arq->io_context && arq->io_context->aic) + atomic_inc(&arq->io_context->aic->nr_dispatched); + ad->nr_dispatched++; +} + +/* + * as_dispatch_request selects the best request according to + * read/write expire, batch expire, etc, and moves it to the dispatch + * queue. Returns 1 if a request was found, 0 otherwise. + */ +static int as_dispatch_request(request_queue_t *q, int force) +{ + struct as_data *ad = q->elevator->elevator_data; + struct as_rq *arq; + const int reads = !list_empty(&ad->fifo_list[REQ_SYNC]); + const int writes = !list_empty(&ad->fifo_list[REQ_ASYNC]); + + if (unlikely(force)) { + /* + * Forced dispatch, accounting is useless. Reset + * accounting states and dump fifo_lists. Note that + * batch_data_dir is reset to REQ_SYNC to avoid + * screwing write batch accounting as write batch + * accounting occurs on W->R transition. + */ + int dispatched = 0; + + ad->batch_data_dir = REQ_SYNC; + ad->changed_batch = 0; + ad->new_batch = 0; + + while (ad->next_arq[REQ_SYNC]) { + as_move_to_dispatch(ad, ad->next_arq[REQ_SYNC]); + dispatched++; + } + ad->last_check_fifo[REQ_SYNC] = jiffies; + + while (ad->next_arq[REQ_ASYNC]) { + as_move_to_dispatch(ad, ad->next_arq[REQ_ASYNC]); + dispatched++; + } + ad->last_check_fifo[REQ_ASYNC] = jiffies; + + return dispatched; + } + + /* Signal that the write batch was uncontended, so we can't time it */ + if (ad->batch_data_dir == REQ_ASYNC && !reads) { + if (ad->current_write_count == 0 || !writes) + ad->write_batch_idled = 1; + } + + if (!(reads || writes) + || ad->antic_status == ANTIC_WAIT_REQ + || ad->antic_status == ANTIC_WAIT_NEXT + || ad->changed_batch) + return 0; + + if (!(reads && writes && as_batch_expired(ad)) ) { + /* + * batch is still running or no reads or no writes + */ + arq = ad->next_arq[ad->batch_data_dir]; + + if (ad->batch_data_dir == REQ_SYNC && ad->antic_expire) { |