[PATCH] 01/05 Implement generic dispatch queue

Implements generic dispatch queue which can replace all
dispatch queues implemented by each iosched.  This reduces
code duplication, eases enforcing semantics over dispatch
queue, and simplifies specific ioscheds.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 170 insertions, 72 deletions

diff --git a/drivers/block/elevator.c b/drivers/block/elevator.c
index 4144f30d82a9..a27555908d35 100644
--- a/drivers/block/elevator.c
+++ b/drivers/block/elevator.c
@@ -40,6 +40,11 @@
 static DEFINE_SPINLOCK(elv_list_lock);
 static LIST_HEAD(elv_list);
 
+static inline sector_t rq_last_sector(struct request *rq)
+{
+        return rq->sector + rq->nr_sectors;
+}
+
 /*
  * can we safely merge with this request?
  */
@@ -143,6 +148,9 @@ static int elevator_attach(request_queue_t *q, struct elevator_type *e,
         INIT_LIST_HEAD(&q->queue_head);
         q->last_merge = NULL;
         q->elevator = eq;
+        q->last_sector = 0;
+        q->boundary_rq = NULL;
+        q->max_back_kb = 0;
 
         if (eq->ops->elevator_init_fn)
                 ret = eq->ops->elevator_init_fn(q, eq);
@@ -225,6 +233,48 @@ void elevator_exit(elevator_t *e)
         kfree(e);
 }
 
+/*
+ * Insert rq into dispatch queue of q.  Queue lock must be held on
+ * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
+ * appended to the dispatch queue.  To be used by specific elevators.
+ */
+void elv_dispatch_insert(request_queue_t *q, struct request *rq, int sort)
+{
+        sector_t boundary;
+        unsigned max_back;
+        struct list_head *entry;
+
+        if (!sort) {
+                /* Specific elevator is performing sort.  Step away. */
+                q->last_sector = rq_last_sector(rq);
+                q->boundary_rq = rq;
+                list_add_tail(&rq->queuelist, &q->queue_head);
+                return;
+        }
+
+        boundary = q->last_sector;
+        max_back = q->max_back_kb * 2;
+        boundary = boundary > max_back ? boundary - max_back : 0;
+
+        list_for_each_prev(entry, &q->queue_head) {
+                struct request *pos = list_entry_rq(entry);
+
+                if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
+                        break;
+                if (rq->sector >= boundary) {
+                        if (pos->sector < boundary)
+                                continue;
+                } else {
+                        if (pos->sector >= boundary)
+                                break;
+                }
+                if (rq->sector >= pos->sector)
+                        break;
+        }
+
+        list_add(&rq->queuelist, entry);
+}
+
 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
         elevator_t *e = q->elevator;
@@ -255,13 +305,7 @@ void elv_merge_requests(request_queue_t *q, struct request *rq,
                 e->ops->elevator_merge_req_fn(q, rq, next);
 }
 
-/*
- * For careful internal use by the block layer. Essentially the same as
- * a requeue in that it tells the io scheduler that this request is not
- * active in the driver or hardware anymore, but we don't want the request
- * added back to the scheduler. Function is not exported.
- */
-void elv_deactivate_request(request_queue_t *q, struct request *rq)
+void elv_requeue_request(request_queue_t *q, struct request *rq)
 {
         elevator_t *e = q->elevator;
 
@@ -269,19 +313,14 @@ void elv_deactivate_request(request_queue_t *q, struct request *rq)
          * it already went through dequeue, we need to decrement the
          * in_flight count again
          */
-        if (blk_account_rq(rq))
+        if (blk_account_rq(rq)) {
                 q->in_flight--;
+                if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
+                        e->ops->elevator_deactivate_req_fn(q, rq);
+        }
 
         rq->flags &= ~REQ_STARTED;
 
-        if (e->ops->elevator_deactivate_req_fn)
-                e->ops->elevator_deactivate_req_fn(q, rq);
-}
-
-void elv_requeue_request(request_queue_t *q, struct request *rq)
-{
-        elv_deactivate_request(q, rq);
-
         /*
          * if this is the flush, requeue the original instead and drop the flush
          */
@@ -290,55 +329,89 @@ void elv_requeue_request(request_queue_t *q, struct request *rq)
                 rq = rq->end_io_data;
         }
 
-        /*
-         * the request is prepped and may have some resources allocated.
-         * allowing unprepped requests to pass this one may cause resource
-         * deadlock.  turn on softbarrier.
-         */
-        rq->flags |= REQ_SOFTBARRIER;
-
-        /*
-         * if iosched has an explicit requeue hook, then use that. otherwise
-         * just put the request at the front of the queue
-         */
-        if (q->elevator->ops->elevator_requeue_req_fn)
-                q->elevator->ops->elevator_requeue_req_fn(q, rq);
-        else
-                __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
+        __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 }
 
 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
                        int plug)
 {
-        /*
-         * barriers implicitly indicate back insertion
-         */
-        if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&
-            where == ELEVATOR_INSERT_SORT)
-                where = ELEVATOR_INSERT_BACK;
+        if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
+                /*
+                 * barriers implicitly indicate back insertion
+                 */
+                if (where == ELEVATOR_INSERT_SORT)
+                        where = ELEVATOR_INSERT_BACK;
+
+                /*
+                 * this request is scheduling boundary, update last_sector
+                 */
+                if (blk_fs_request(rq)) {
+                        q->last_sector = rq_last_sector(rq);
+                        q->boundary_rq = rq;
+                }
+        }
 
         if (plug)
                 blk_plug_device(q);
 
         rq->q = q;
 
-        if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {
-                q->elevator->ops->elevator_add_req_fn(q, rq, where);
-
-                if (blk_queue_plugged(q)) {
-                        int nrq = q->rq.count[READ] + q->rq.count[WRITE]
-                                  - q->in_flight;
-
-                        if (nrq >= q->unplug_thresh)
-                                __generic_unplug_device(q);
-                }
-        } else
+        if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
                 /*
                  * if drain is set, store the request "locally". when the drain
                  * is finished, the requests will be handed ordered to the io
                  * scheduler
                  */
                 list_add_tail(&rq->queuelist, &q->drain_list);
+                return;
+        }
+
+        switch (where) {
+        case ELEVATOR_INSERT_FRONT:
+                rq->flags |= REQ_SOFTBARRIER;
+
+                list_add(&rq->queuelist, &q->queue_head);
+                break;
+
+        case ELEVATOR_INSERT_BACK:
+                rq->flags |= REQ_SOFTBARRIER;
+
+                while (q->elevator->ops->elevator_dispatch_fn(q, 1))
+                        ;
+                list_add_tail(&rq->queuelist, &q->queue_head);
+                /*
+                 * We kick the queue here for the following reasons.
+                 * - The elevator might have returned NULL previously
+                 *   to delay requests and returned them now.  As the
+                 *   queue wasn't empty before this request, ll_rw_blk
+                 *   won't run the queue on return, resulting in hang.
+                 * - Usually, back inserted requests won't be merged
+                 *   with anything.  There's no point in delaying queue
+                 *   processing.
+                 */
+                blk_remove_plug(q);
+                q->request_fn(q);
+                break;
+
+        case ELEVATOR_INSERT_SORT:
+                BUG_ON(!blk_fs_request(rq));
+                rq->flags |= REQ_SORTED;
+                q->elevator->ops->elevator_add_req_fn(q, rq);
+                break;
+
+        default:
+                printk(KERN_ERR "%s: bad insertion point %d\n",
+                       __FUNCTION__, where);
+                BUG();
+        }
+
+        if (blk_queue_plugged(q)) {
+                int nrq = q->rq.count[READ] + q->rq.count[WRITE]
+                        - q->in_flight;
+
+                if (nrq >= q->unplug_thresh)
+                        __generic_unplug_device(q);
+        }
 }
 
 void elv_add_request(request_queue_t *q, struct request *rq, int where,
@@ -353,13 +426,19 @@ void elv_add_request(request_queue_t *q, struct request *rq, int where,
 
 static inline struct request *__elv_next_request(request_queue_t *q)
 {
-        struct request *rq = q->elevator->ops->elevator_next_req_fn(q);
+        struct request *rq;
+
+        if (unlikely(list_empty(&q->queue_head) &&
+                     !q->elevator->ops->elevator_dispatch_fn(q, 0)))
+                return NULL;
+
+        rq = list_entry_rq(q->queue_head.next);
 
         /*
          * if this is a barrier write and the device has to issue a
          * flush sequence to support it, check how far we are
          */
-        if (rq && blk_fs_request(rq) && blk_barrier_rq(rq)) {
+        if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
                 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
 
                 if (q->ordered == QUEUE_ORDERED_FLUSH &&
@@ -376,16 +455,34 @@ struct request *elv_next_request(request_queue_t *q)
         int ret;
 
         while ((rq = __elv_next_request(q)) != NULL) {
-                /*
-                 * just mark as started even if we don't start it, a request
-                 * that has been delayed should not be passed by new incoming
-                 * requests
-                 */
-                rq->flags |= REQ_STARTED;
+                if (!(rq->flags & REQ_STARTED)) {
+                        elevator_t *e = q->elevator;
+
+                        /*
+                         * This is the first time the device driver
+                         * sees this request (possibly after
+                         * requeueing).  Notify IO scheduler.
+                         */
+                        if (blk_sorted_rq(rq) &&
+                            e->ops->elevator_activate_req_fn)
+                                e->ops->elevator_activate_req_fn(q, rq);
+
+                        /*
+                         * just mark as started even if we don't start
+                         * it, a request that has been delayed should
+                         * not be passed by new incoming requests
+                         */
+                        rq->flags |= REQ_STARTED;
+                }
 
                 if (rq == q->last_merge)
                         q->last_merge = NULL;
 
+                if (!q->boundary_rq || q->boundary_rq == rq) {
+                        q->last_sector = rq_last_sector(rq);
+                        q->boundary_rq = NULL;
+                }
+
                 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
                         break;
 
@@ -396,9 +493,9 @@ struct request *elv_next_request(request_queue_t *q)
                         /*
                          * the request may have been (partially) prepped.
                          * we need to keep this request in the front to
-                         * avoid resource deadlock.  turn on softbarrier.
+                         * avoid resource deadlock.  REQ_STARTED will
+                         * prevent other fs requests from passing this one.
                          */
-                        rq->flags |= REQ_SOFTBARRIER;
                         rq = NULL;
                         break;
                 } else if (ret == BLKPREP_KILL) {
@@ -421,16 +518,16 @@ struct request *elv_next_request(request_queue_t *q)
         return rq;
 }
 
-void elv_remove_request(request_queue_t *q, struct request *rq)
+void elv_dequeue_request(request_queue_t *q, struct request *rq)
 {
-        elevator_t *e = q->elevator;
+        BUG_ON(list_empty(&rq->queuelist));
+
+        list_del_init(&rq->queuelist);
 
         /*
          * the time frame between a request being removed from the lists
          * and to it is freed is accounted as io that is in progress at
-         * the driver side. note that we only account requests that the
-         * driver has seen (REQ_STARTED set), to avoid false accounting
-         * for request-request merges
+         * the driver side.
          */
         if (blk_account_rq(rq))
                 q->in_flight++;
@@ -444,19 +541,19 @@ void elv_remove_request(request_queue_t *q, struct request *rq)
          */
         if (rq == q->last_merge)
                 q->last_merge = NULL;
-
-        if (e->ops->elevator_remove_req_fn)
-                e->ops->elevator_remove_req_fn(q, rq);
 }
 
 int elv_queue_empty(request_queue_t *q)
 {
         elevator_t *e = q->elevator;
 
+        if (!list_empty(&q->queue_head))
+                return 0;
+
         if (e->ops->elevator_queue_empty_fn)
                 return e->ops->elevator_queue_empty_fn(q);
 
-        return list_empty(&q->queue_head);
+        return 1;
 }
 
 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
@@ -528,11 +625,11 @@ void elv_completed_request(request_queue_t *q, struct request *rq)
         /*
          * request is released from the driver, io must be done
          */
-        if (blk_account_rq(rq))
+        if (blk_account_rq(rq)) {
                 q->in_flight--;
-
-        if (e->ops->elevator_completed_req_fn)
-                e->ops->elevator_completed_req_fn(q, rq);
+                if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
+                        e->ops->elevator_completed_req_fn(q, rq);
+        }
 }
 
 int elv_register_queue(struct request_queue *q)
@@ -705,11 +802,12 @@ ssize_t elv_iosched_show(request_queue_t *q, char *name)
         return len;
 }
 
+EXPORT_SYMBOL(elv_dispatch_insert);
 EXPORT_SYMBOL(elv_add_request);
 EXPORT_SYMBOL(__elv_add_request);
 EXPORT_SYMBOL(elv_requeue_request);
 EXPORT_SYMBOL(elv_next_request);
-EXPORT_SYMBOL(elv_remove_request);
+EXPORT_SYMBOL(elv_dequeue_request);
 EXPORT_SYMBOL(elv_queue_empty);
 EXPORT_SYMBOL(elv_completed_request);
 EXPORT_SYMBOL(elevator_exit);