Patch from Nick Piggin <piggin@cyberone.com.au>
Now 1 AFAIKS forward decl which really can't go. Better arrangement. More
comments. The last BUG_ON fix is included in this, but other than that there
should be no functional changes.
drivers/block/as-iosched.c | 1083 ++++++++++++++++++++++-----------------------
1 files changed, 546 insertions(+), 537 deletions(-)
diff -puN drivers/block/as-iosched.c~as-cleanup-2 drivers/block/as-iosched.c
--- 25/drivers/block/as-iosched.c~as-cleanup-2 2003-03-16 19:49:24.000000000 -0800
+++ 25-akpm/drivers/block/as-iosched.c 2003-03-16 19:49:24.000000000 -0800
@@ -81,15 +81,6 @@ static unsigned long write_batch_expire
*/
static unsigned long antic_expire = HZ / 100;
-enum anticipation_states {
- 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 */
-};
-
/*
* This is the per-process anticipatory I/O scheduler state. It is refcounted
* and kmalloc'ed.
@@ -158,12 +149,15 @@ struct as_data {
unsigned long antic_expire;
};
-enum arq_states {
- 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 */
+#define list_entry_fifo(ptr) list_entry((ptr), struct as_rq, fifo)
+
+enum anticipation_states {
+ 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 */
};
/*
@@ -192,7 +186,15 @@ struct as_rq {
struct list_head fifo;
unsigned long expires;
- unsigned long state;
+ unsigned long state; /* debug only */
+};
+
+enum arq_states {
+ 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 */
};
#define RQ_DATA(rq) ((struct as_rq *) (rq)->elevator_private)
@@ -389,40 +391,6 @@ static struct as_rq *as_find_first_arq(s
}
}
-static struct as_rq *
-as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2);
-
-/*
- * as_find_next_arq finds the next request after @prev in elevator order.
- */
-static struct as_rq *as_find_next_arq(struct as_data *ad, struct as_rq *last)
-{
- const int data_dir = rq_data_dir(last->request);
- 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;
-}
-
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;
@@ -446,7 +414,6 @@ static struct as_rq *__as_add_arq_rb(str
}
static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq);
-
/*
* Aad 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
@@ -460,6 +427,7 @@ static void as_add_arq_rb(struct as_data
arq->rb_key = rq_rb_key(rq);
+ /* This can be caused by direct IO */
while ((alias = __as_add_arq_rb(ad, arq)))
as_move_to_dispatch(ad, alias);
@@ -494,395 +462,173 @@ as_find_arq_rb(struct as_data *ad, secto
return NULL;
}
-static void as_antic_waitnext(struct as_data *ad);
+/*
+ * IO Scheduler proper
+ */
+
+#define MAXBACK (512 * 1024) /* Maximum distance a process can seek backward
+ from a previous request it has made. No
+ seeking backward between processes allowed */
/*
- * as_update_iohist keeps a decaying histogram of IO thinktimes, and
- * updates @aic->mean_thinktime based on that. It is called when a new
- * request is queued.
+ * 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 void as_update_iohist(struct as_io_context *aic)
+static struct as_rq *
+as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2)
{
- unsigned i;
- unsigned long thinktime;
- unsigned long total = 0;
- unsigned long num = 0;
+ 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 (aic == NULL)
- return;
+ if (arq1 == NULL || arq1 == arq2)
+ return arq2;
+ if (arq2 == NULL)
+ return arq1;
- if (test_bit(AS_TASK_IORUNNING, &aic->state)) {
- thinktime = jiffies - aic->last_end_request;
- thinktime = min(thinktime, MAX_THINKTIME-1);
- aic->thinktime[thinktime] += 256; /* fixed point: 1.0 == 1<<8 */
+ data_dir = rq_data_dir(arq1->request);
- for (i = 0; i < MAX_THINKTIME; i++) {
- unsigned long tt = aic->thinktime[i];
- total += i*tt;
- num += tt;
+ last = ad->last_sector[data_dir];
+ s1 = arq1->request->sector;
+ s2 = arq2->request->sector;
- aic->thinktime[i] = (tt>>1) + (tt>>2); /* 75% decay */
- }
- /* fixed point factor is cancelled here */
- if (num)
- aic->mean_thinktime = total / num;
+ BUG_ON(data_dir != rq_data_dir(arq2->request));
+
+ /*
+ * 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. Only for reads and only between reads
+ * from the same process!
+ */
+ if (s1 >= last)
+ d1 = s1 - last;
+ else if (data_dir == READ
+ && ad->as_io_context == arq1->as_io_context
+ && s1+maxback >= last)
+ d1 = (last - s1)*2;
+ else {
+ r1_wrap = 1;
+ d1 = 0; /* shut up, gcc */
+ }
+
+ if (s2 >= last)
+ d2 = s2 - last;
+ else if (data_dir == READ
+ && ad->as_io_context == arq2->as_io_context
+ && s2+maxback >= last)
+ d2 = (last - s2)*2;
+ 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;
}
}
/*
- * Look Ma, no comment!
+ * as_find_next_arq finds the next request after @prev in elevator order.
+ * this with as_choose_arq form the basis for how the scheduler chooses
+ * what request to process next. Anticipation works on top of this.
*/
-
-static void as_complete_arq(struct as_data *ad, struct as_rq *arq)
+static struct as_rq *as_find_next_arq(struct as_data *ad, struct as_rq *last)
{
- if (!arq->as_io_context)
- return;
+ const int data_dir = rq_data_dir(last->request);
+ 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;
- if (rq_data_dir(arq->request) == READ) {
- set_bit(AS_TASK_IORUNNING, &arq->as_io_context->state);
- arq->as_io_context->last_end_request = jiffies;
- }
+ BUG_ON(!ON_RB(&last->rb_node));
- if (ad->as_io_context == arq->as_io_context) {
- ad->antic_start = jiffies;
- ad->aic_finished = 1;
- if (ad->antic_status == ANTIC_WAIT_REQ) {
- /*
- * We were waiting on this request, now anticipate
- * the next one
- */
- as_antic_waitnext(ad);
- }
+ 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;
}
- put_as_io_context(&arq->as_io_context);
-}
-static void as_update_arq(struct as_data *ad, struct as_rq *arq);
+ ret = as_choose_req(ad, arq_next, arq_prev);
+
+ return ret;
+}
/*
- * add arq to rbtree and fifo
+ * anticipatory scheduling functions follow
*/
-static void as_add_request(struct as_data *ad, struct as_rq *arq)
-{
- const int data_dir = rq_data_dir(arq->request);
-
- arq->as_io_context = get_as_io_context();
- if (arq->as_io_context) {
- atomic_inc(&arq->as_io_context->nr_queued);
- if (data_dir == READ)
- as_update_iohist(arq->as_io_context);
- }
+/*
+ * 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;
- as_add_arq_rb(ad, arq);
+ delta_jif = jiffies - ad->antic_start;
+ if (unlikely(delta_jif < 0))
+ delta_jif = -delta_jif;
+ if (delta_jif < ad->antic_expire)
+ return 0;
- /*
- * set expire time (only used for reads) and add to fifo list
- */
- arq->expires = jiffies + ad->fifo_expire[data_dir];
- list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]);
- arq->state = AS_RQ_QUEUED;
- as_update_arq(ad, arq); /* keep state machine up to date */
+ return 1;
}
/*
- * 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)
+ * as_antic_waitnext starts anticipating that a nice request will soon be
+ * submitted. See also as_antic_waitreq
*/
-static void as_remove_queued_request(request_queue_t *q, struct request *rq)
+static void as_antic_waitnext(struct as_data *ad)
{
- struct as_rq *arq = RQ_DATA(rq);
-
- if (!arq)
- BUG();
- else {
- const int data_dir = rq_data_dir(arq->request);
- struct as_data *ad = q->elevator.elevator_data;
+ unsigned long timeout;
- BUG_ON(arq->state != AS_RQ_QUEUED);
+ BUG_ON(ad->antic_status != ANTIC_OFF
+ && ad->antic_status != ANTIC_WAIT_REQ);
- if (arq->as_io_context) {
- BUG_ON(!atomic_read(&arq->as_io_context->nr_queued));
- atomic_dec(&arq->as_io_context->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);
-
- if (q->last_merge == &rq->queuelist)
- q->last_merge = NULL;
-
- list_del_init(&rq->queuelist);
- }
-
-}
-
-/*
- * as_remove_dispatched_request is called when a driver has completed the
- * request (or it has caused an error), and is finished with it. It assumes
- * the request is on the dispatch queue.
- */
-static void as_remove_request(request_queue_t *q, struct request *rq)
-{
- struct as_rq *arq = RQ_DATA(rq);
- struct as_data *ad = q->elevator.elevator_data;
-
- if (q->last_merge == &rq->queuelist)
- q->last_merge = NULL;
-
- list_del_init(&rq->queuelist);
-
- if (arq) {
- list_del_init(&arq->fifo);
- as_del_arq_hash(arq);
- as_del_arq_rb(ad, arq);
- if (arq->as_io_context) {
- WARN_ON(!atomic_read(&arq->as_io_context->nr_dispatched));
- atomic_dec(&arq->as_io_context->nr_dispatched);
- }
- as_complete_arq(ad, arq);
- }
-}
-
-static int
-as_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
-{
- struct as_data *ad = q->elevator.elevator_data;
- struct request *__rq;
- int ret;
-
- /*
- * try last_merge to avoid going to hash
- */
- ret = elv_try_last_merge(q, bio);
- if (ret != ELEVATOR_NO_MERGE) {
- __rq = list_entry_rq(q->last_merge);
- goto out_insert;
- }
-
- /*
- * see if the merge hash can satisfy a back merge
- */
- __rq = as_find_arq_hash(ad, bio->bi_sector);
- if (__rq) {
- BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
-
- if (elv_rq_merge_ok(__rq, bio)) {
- ret = ELEVATOR_BACK_MERGE;
- goto out;
- }
- }
-
- /*
- * check for front merge
- */
- if (ad->front_merges) {
- sector_t rb_key = bio->bi_sector + bio_sectors(bio);
-
- __rq = as_find_arq_rb(ad, rb_key, bio_data_dir(bio));
- if (__rq) {
- BUG_ON(rb_key != rq_rb_key(__rq));
-
- if (elv_rq_merge_ok(__rq, bio)) {
- ret = ELEVATOR_FRONT_MERGE;
- goto out;
- }
- }
- }
-
- return ELEVATOR_NO_MERGE;
-out:
- q->last_merge = &__rq->queuelist;
-out_insert:
- *insert = &__rq->queuelist;
- return ret;
-}
-
-static void as_merged_request(request_queue_t *q, struct request *req)
-{
- struct as_data *ad = q->elevator.elevator_data;
- struct as_rq *arq = RQ_DATA(req);
-
- /*
- * hash always needs to be repositioned, key is end sector
- */
- as_del_arq_hash(arq);
- as_add_arq_hash(ad, arq);
-
- /*
- * if the merge was a front merge, we need to reposition request
- */
- if (rq_rb_key(req) != arq->rb_key) {
- as_del_arq_rb(ad, arq);
- as_add_arq_rb(ad, arq);
- /*
- * Note! At this stage of this and the next function, our next
- * request may not be optimal - eg the request may have "grown"
- * behind the disk head. We currently don't bother adjusting.
- */
- }
-
- q->last_merge = &req->queuelist;
-}
-
-static void
-as_merged_requests(request_queue_t *q, struct request *req,
- struct request *next)
-{
- struct as_data *ad = q->elevator.elevator_data;
- struct as_rq *arq = RQ_DATA(req);
- struct as_rq *anext = RQ_DATA(next);
-
- BUG_ON(!arq);
- BUG_ON(!anext);
-
- /*
- * reposition arq (this is the merged request) in hash, and in rbtree
- * in case of a front merge
- */
- as_del_arq_hash(arq);
- as_add_arq_hash(ad, arq);
-
- if (rq_rb_key(req) != arq->rb_key) {
- as_del_arq_rb(ad, arq);
- as_add_arq_rb(ad, arq);
- }
-
- /*
- * if anext expires before arq, assign its expire time to arq
- * and move into anext position (anext will be deleted) in fifo
- */
- if (!list_empty(&arq->fifo) && !list_empty(&anext->fifo)) {
- if (time_before(anext->expires, arq->expires)) {
- list_move(&arq->fifo, &anext->fifo);
- arq->expires = anext->expires;
- /*
- * Don't copy here but swap, because when anext is
- * removed below, it must contain the unused context
- */
- swap_as_io_context(&arq->as_io_context,
- &anext->as_io_context);
- }
- }
-
- /*
- * kill knowledge of next, this one is a goner
- */
- as_remove_queued_request(q, next);
- put_as_io_context(&anext->as_io_context);
-}
-
-static void as_antic_stop(struct as_data *ad);
-
-/*
- * move an entry to dispatch queue
- */
-static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq)
-{
- const int data_dir = rq_data_dir(arq->request);
-
- 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] = arq->request->sector
- + arq->request->nr_sectors;
-
- if (data_dir == READ) {
- /* In case we have to anticipate after this */
- copy_as_io_context(&ad->as_io_context, &arq->as_io_context);
- ad->aic_finished = 0;
- } else
- put_as_io_context(&ad->as_io_context);
-
- ad->next_arq[data_dir] = as_find_next_arq(ad, arq);
-
- /*
- * take it off the sort and fifo list, add to dispatch queue
- */
- as_remove_queued_request(ad->q, arq->request);
- list_add_tail(&arq->request->queuelist, ad->dispatch);
- if (arq->as_io_context)
- atomic_inc(&arq->as_io_context->nr_dispatched);
-
- BUG_ON(arq->state != AS_RQ_QUEUED);
- arq->state = AS_RQ_DISPATCHED;
-}
-
-#define list_entry_fifo(ptr) list_entry((ptr), struct as_rq, fifo)
-
-/*
- * 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.
- *
- * 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_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);
-}
-
-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_batch_expired returns true if the current batch has expired.
- */
-static inline int as_batch_expired(struct as_data *ad)
-{
- return time_after(jiffies, ad->current_batch_expires);
+ timeout = ad->antic_start + ad->antic_expire;
+#if 0 /* TODO unif me. This should be fixed. */
+ timeout = min(timeout, ad->current_batch_expires);
+#endif
+ mod_timer(&ad->antic_timer, timeout);
+
+ ad->antic_status = ANTIC_WAIT_NEXT;
}
/*
- * anticipatory scheduling functions follow
+ * 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 int as_queue_notready(request_queue_t *q);
-
static void as_antic_waitreq(struct as_data *ad)
{
BUG_ON(ad->antic_status == ANTIC_FINISHED);
@@ -896,46 +642,6 @@ static void as_antic_waitreq(struct as_d
}
}
-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;
-#if 0
- /* FIX THIS!!! */
- timeout = min(timeout, ad->current_batch_expires);
-#endif
- mod_timer(&ad->antic_timer, timeout);
-
- ad->antic_status = ANTIC_WAIT_NEXT;
-}
-
-/*
- * This is executed in a "deferred" process context, by kblockd. It calls the
- * driver's request_fn so the driver can submit that request.
- *
- * IMPORTANT! Thisguy will reenter the elevator, so set up all queue global
- * state before calling, and don't rely on any state over calls.
- *
- * FIXME! dispatch queue is not a queue at all!
- * Andrew! as_queue_notready does not _try_ to move a request to dispatch
- * list, in fact it tries not to! Unfortunately it sometimes must in order
- * to guarantee elv_next_request will return !NULL after a ready indication.
- */
-static void as_work_handler(void *data)
-{
- struct request_queue *q = data;
- unsigned long flags;
-
- spin_lock_irqsave(q->queue_lock, flags);
- if (!as_queue_notready(q))
- q->request_fn(q);
- spin_unlock_irqrestore(q->queue_lock, flags);
-}
-
/*
* 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.
@@ -948,6 +654,7 @@ static void as_antic_stop(struct as_data
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);
}
}
@@ -1005,7 +712,7 @@ static int as_close_req(struct as_data *
*
* If the task which has submitted the request has exitted, break anticipation.
*
- * If this task has queued some other reads, do not enter enticipation.
+ * 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)
{
@@ -1051,6 +758,75 @@ static int as_can_break_anticipation(str
}
/*
+ * 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->as_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 (arq && 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;
+}
+
+/*
+ * as_update_iohist keeps a decaying histogram of IO thinktimes, and
+ * updates @aic->mean_thinktime based on that. It is called when a new
+ * request is queued.
+ */
+static void as_update_iohist(struct as_io_context *aic)
+{
+ unsigned i;
+ unsigned long thinktime;
+ unsigned long total = 0;
+ unsigned long num = 0;
+
+ if (aic == NULL)
+ return;
+
+ if (test_bit(AS_TASK_IORUNNING, &aic->state)) {
+ thinktime = jiffies - aic->last_end_request;
+ thinktime = min(thinktime, MAX_THINKTIME-1);
+ aic->thinktime[thinktime] += 256; /* fixed point: 1.0 == 1<<8 */
+
+ for (i = 0; i < MAX_THINKTIME; i++) {
+ unsigned long tt = aic->thinktime[i];
+ total += i*tt;
+ num += tt;
+
+ aic->thinktime[i] = (tt>>1) + (tt>>2); /* 75% decay */
+ }
+ /* fixed point factor is cancelled here */
+ if (num)
+ aic->mean_thinktime = total / num;
+ }
+}
+
+/*
* 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"
@@ -1110,120 +886,178 @@ static void as_update_arq(struct as_data
}
/*
- * as_can_anticipate indicates weather we should either run arq
- * or keep anticipating a better request.
+ * as_complete_arq is to be called when a request has completed and returned
+ * something to the requesting process, be it an error or data.
*/
-static int as_can_anticipate(struct as_data *ad, struct as_rq *arq)
+static void as_complete_arq(struct as_data *ad, struct as_rq *arq)
{
- BUG_ON(ad->antic_status == ANTIC_WAIT_REQ ||
- ad->antic_status == ANTIC_WAIT_NEXT);
+ if (!arq->as_io_context)
+ return;
- if (!ad->as_io_context)
- /*
- * Last request submitted was a write
- */
- return 0;
+ if (rq_data_dir(arq->request) == READ) {
+ set_bit(AS_TASK_IORUNNING, &arq->as_io_context->state);
+ arq->as_io_context->last_end_request = jiffies;
+ }
- if (ad->antic_status == ANTIC_FINISHED)
- /*
- * Don't restart if we have just finished. Run the next request
- */
- return 0;
+ if (ad->as_io_context == arq->as_io_context) {
+ ad->antic_start = jiffies;
+ ad->aic_finished = 1;
+ if (ad->antic_status == ANTIC_WAIT_REQ) {
+ /*
+ * We were waiting on this request, now anticipate
+ * the next one
+ */
+ as_antic_waitnext(ad);
+ }
+ }
+ put_as_io_context(&arq->as_io_context);
+}
+
+/*
+ * 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);
+
+ if (!arq)
+ BUG();
+ else {
+ const int data_dir = rq_data_dir(arq->request);
+ struct as_data *ad = q->elevator.elevator_data;
+
+ BUG_ON(arq->state != AS_RQ_QUEUED);
+
+ if (arq->as_io_context) {
+ BUG_ON(!atomic_read(&arq->as_io_context->nr_queued));
+ atomic_dec(&arq->as_io_context->nr_queued);
+ }
- if (arq && as_can_break_anticipation(ad, arq))
/*
- * This request is a good candidate. Don't keep anticipating,
- * run it.
+ * 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);
+
+ if (q->last_merge == &rq->queuelist)
+ q->last_merge = NULL;
+
+ list_del_init(&rq->queuelist);
+ }
+
+}
+
+/*
+ * as_remove_request is called when a driver has completed the request
+ * (or it has caused an error), and is finished with it. It assumes
+ * the request is on the dispatch queue.
+ */
+static void as_remove_request(request_queue_t *q, struct request *rq)
+{
+ struct as_rq *arq = RQ_DATA(rq);
+ struct as_data *ad = q->elevator.elevator_data;
+
+ if (q->last_merge == &rq->queuelist)
+ q->last_merge = NULL;
+
+ list_del_init(&rq->queuelist);
+
+ if (arq) {
+ list_del_init(&arq->fifo);
+ as_del_arq_hash(arq);
+ as_del_arq_rb(ad, arq);
+ if (arq->as_io_context) {
+ WARN_ON(!atomic_read(&arq->as_io_context->nr_dispatched));
+ atomic_dec(&arq->as_io_context->nr_dispatched);
+ }
+ as_complete_arq(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;
- /*
- * OK from here, we haven't finished, and don't have a decent request!
- * Status is ANTIC_OFF so start waiting.
- */
+ ad->last_check_fifo[adir] = jiffies;
- return 1;
+ if (list_empty(&ad->fifo_list[adir]))
+ return 0;
+
+ arq = list_entry_fifo(ad->fifo_list[adir].next);
+
+ return time_after(jiffies, arq->expires);
}
-#define MAXBACK (512 * 1024)
+/*
+ * 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)
+{
+ return time_after(jiffies, ad->current_batch_expires);
+}
/*
- * 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
+ * move an entry to dispatch queue
*/
-static struct as_rq *
-as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2)
+static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq)
{
- 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;
+ const int data_dir = rq_data_dir(arq->request);
+
+ BUG_ON(!ON_RB(&arq->rb_node));
- if (arq1 == NULL || arq1 == arq2)
- return arq2;
- if (arq2 == NULL)
- return arq1;
+ as_antic_stop(ad);
+ ad->antic_status = ANTIC_OFF;
- data_dir = rq_data_dir(arq1->request);
+ /*
+ * This has to be set in order to be correctly updated by
+ * as_find_next_arq
+ */
+ ad->last_sector[data_dir] = arq->request->sector
+ + arq->request->nr_sectors;
- last = ad->last_sector[data_dir];
- s1 = arq1->request->sector;
- s2 = arq2->request->sector;
+ if (data_dir == READ) {
+ /* In case we have to anticipate after this */
+ copy_as_io_context(&ad->as_io_context, &arq->as_io_context);
+ ad->aic_finished = 0;
+ } else
+ put_as_io_context(&ad->as_io_context);
- BUG_ON(data_dir != rq_data_dir(arq2->request));
+ ad->next_arq[data_dir] = as_find_next_arq(ad, arq);
/*
- * 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. Only for reads and only between reads
- * from the same process!
+ * take it off the sort and fifo list, add to dispatch queue
*/
- if (s1 >= last)
- d1 = s1 - last;
- else if (data_dir == READ
- && ad->as_io_context == arq1->as_io_context
- && s1+maxback >= last)
- d1 = (last - s1)*2;
- else {
- r1_wrap = 1;
- d1 = 0; /* shut up, gcc */
- }
-
- if (s2 >= last)
- d2 = s2 - last;
- else if (data_dir == READ
- && ad->as_io_context == arq2->as_io_context
- && s2+maxback >= last)
- d2 = (last - s2)*2;
- else {
- r2_wrap = 1;
- d2 = 0;
- }
+ as_remove_queued_request(ad->q, arq->request);
+ list_add_tail(&arq->request->queuelist, ad->dispatch);
+ if (arq->as_io_context)
+ atomic_inc(&arq->as_io_context->nr_dispatched);
- /* 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;
- }
+ BUG_ON(arq->state != AS_RQ_QUEUED);
+ arq->state = AS_RQ_DISPATCHED;
}
/*
@@ -1312,7 +1146,6 @@ dispatch_writes:
return 0;
dispatch_request:
-
/*
* If a request has expired, service it.
*/
@@ -1349,6 +1182,32 @@ static struct request *as_next_request(r
return rq;
}
+/*
+ * add arq to rbtree and fifo
+ */
+static void as_add_request(struct as_data *ad, struct as_rq *arq)
+{
+ const int data_dir = rq_data_dir(arq->request);
+
+ arq->as_io_context = get_as_io_context();
+ if (arq->as_io_context) {
+ atomic_inc(&arq->as_io_context->nr_queued);
+
+ if (data_dir == READ)
+ as_update_iohist(arq->as_io_context);
+ }
+
+ as_add_arq_rb(ad, arq);
+
+ /*
+ * set expire time (only used for reads) and add to fifo list
+ */
+ arq->expires = jiffies + ad->fifo_expire[data_dir];
+ list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]);
+ arq->state = AS_RQ_QUEUED;
+ as_update_arq(ad, arq); /* keep state machine up to date */
+}
+
static void
as_insert_request(request_queue_t *q, struct request *rq,
struct list_head *insert_here)
@@ -1444,6 +1303,154 @@ as_latter_request(request_queue_t *q, st
return ret;
}
+static int
+as_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
+{
+ struct as_data *ad = q->elevator.elevator_data;
+ struct request *__rq;
+ int ret;
+
+ /*
+ * try last_merge to avoid going to hash
+ */
+ ret = elv_try_last_merge(q, bio);
+ if (ret != ELEVATOR_NO_MERGE) {
+ __rq = list_entry_rq(q->last_merge);
+ goto out_insert;
+ }
+
+ /*
+ * see if the merge hash can satisfy a back merge
+ */
+ __rq = as_find_arq_hash(ad, bio->bi_sector);
+ if (__rq) {
+ BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
+
+ if (elv_rq_merge_ok(__rq, bio)) {
+ ret = ELEVATOR_BACK_MERGE;
+ goto out;
+ }
+ }
+
+ /*
+ * check for front merge
+ */
+ if (ad->front_merges) {
+ sector_t rb_key = bio->bi_sector + bio_sectors(bio);
+
+ __rq = as_find_arq_rb(ad, rb_key, bio_data_dir(bio));
+ if (__rq) {
+ BUG_ON(rb_key != rq_rb_key(__rq));
+
+ if (elv_rq_merge_ok(__rq, bio)) {
+ ret = ELEVATOR_FRONT_MERGE;
+ goto out;
+ }
+ }
+ }
+
+ return ELEVATOR_NO_MERGE;
+out:
+ q->last_merge = &__rq->queuelist;
+out_insert:
+ *insert = &__rq->queuelist;
+ return ret;
+}
+
+static void as_merged_request(request_queue_t *q, struct request *req)
+{
+ struct as_data *ad = q->elevator.elevator_data;
+ struct as_rq *arq = RQ_DATA(req);
+
+ /*
+ * hash always needs to be repositioned, key is end sector
+ */
+ as_del_arq_hash(arq);
+ as_add_arq_hash(ad, arq);
+
+ /*
+ * if the merge was a front merge, we need to reposition request
+ */
+ if (rq_rb_key(req) != arq->rb_key) {
+ as_del_arq_rb(ad, arq);
+ as_add_arq_rb(ad, arq);
+ /*
+ * Note! At this stage of this and the next function, our next
+ * request may not be optimal - eg the request may have "grown"
+ * behind the disk head. We currently don't bother adjusting.
+ */
+ }
+
+ q->last_merge = &req->queuelist;
+}
+
+static void
+as_merged_requests(request_queue_t *q, struct request *req,
+ struct request *next)
+{
+ struct as_data *ad = q->elevator.elevator_data;
+ struct as_rq *arq = RQ_DATA(req);
+ struct as_rq *anext = RQ_DATA(next);
+
+ BUG_ON(!arq);
+ BUG_ON(!anext);
+
+ /*
+ * reposition arq (this is the merged request) in hash, and in rbtree
+ * in case of a front merge
+ */
+ as_del_arq_hash(arq);
+ as_add_arq_hash(ad, arq);
+
+ if (rq_rb_key(req) != arq->rb_key) {
+ as_del_arq_rb(ad, arq);
+ as_add_arq_rb(ad, arq);
+ }
+
+ /*
+ * if anext expires before arq, assign its expire time to arq
+ * and move into anext position (anext will be deleted) in fifo
+ */
+ if (!list_empty(&arq->fifo) && !list_empty(&anext->fifo)) {
+ if (time_before(anext->expires, arq->expires)) {
+ list_move(&arq->fifo, &anext->fifo);
+ arq->expires = anext->expires;
+ /*
+ * Don't copy here but swap, because when anext is
+ * removed below, it must contain the unused context
+ */
+ swap_as_io_context(&arq->as_io_context,
+ &anext->as_io_context);
+ }
+ }
+
+ /*
+ * kill knowledge of next, this one is a goner
+ */
+ as_remove_queued_request(q, next);
+ put_as_io_context(&anext->as_io_context);
+}
+
+/*
+ * This is executed in a "deferred" process context, by kblockd. It calls the
+ * driver's request_fn so the driver can submit that request.
+ *
+ * IMPORTANT! This guy will reenter the elevator, so set up all queue global
+ * state before calling, and don't rely on any state over calls.
+ *
+ * FIXME! dispatch queue is not a queue at all!
+ */
+static void as_work_handler(void *data)
+{
+ struct request_queue *q = data;
+ unsigned long flags;
+
+ spin_lock_irqsave(q->queue_lock, flags);
+ if (!as_queue_notready(q))
+ q->request_fn(q);
+ spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
static void as_exit(request_queue_t *q, elevator_t *e)
{
struct as_data *ad = e->elevator_data;
@@ -1527,6 +1534,8 @@ static int as_init(request_queue_t *q, e
ad->batch_expire[WRITE] = write_batch_expire;
e->elevator_data = ad;
+ ad->current_batch_expires = jiffies + ad->batch_expire[READ];
+
for (i = READ; i <= WRITE; i++) {
struct request_list *rl = &q->rq[i];
struct list_head *entry;
_