[BLOCK] as-iosched: update alias handling

Unlike other ioscheds, as-iosched handles alias by chaing them using
rq->queuelist.  As aliased requests are very rare in the first place,
this complicates merge/dispatch handling without meaningful
performance improvement.  This patch updates as-iosched to dump
aliased requests into dispatch queue as other ioscheds do.

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

1 files changed, 25 insertions, 119 deletions

diff --git a/block/as-iosched.c b/block/as-iosched.c
index 43fa20495688..8da3cf66894c 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -182,6 +182,9 @@ struct as_rq {
 
 static kmem_cache_t *arq_pool;
 
+static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq);
+static void as_antic_stop(struct as_data *ad);
+
 /*
  * IO Context helper functions
  */
@@ -370,7 +373,7 @@ static struct as_rq *as_find_first_arq(struct as_data *ad, int data_dir)
  * 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)
+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;
@@ -397,6 +400,16 @@ static struct as_rq *as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
         return NULL;
 }
 
+static void as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
+{
+        struct as_rq *alias;
+
+        while ((unlikely(alias = __as_add_arq_rb(ad, arq)))) {
+                as_move_to_dispatch(ad, alias);
+                as_antic_stop(ad);
+        }
+}
+
 static inline void as_del_arq_rb(struct as_data *ad, struct as_rq *arq)
 {
         if (!ON_RB(&arq->rb_node)) {
@@ -1133,23 +1146,6 @@ static void as_move_to_dispatch(struct as_data *ad, struct as_rq *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);
 
@@ -1326,49 +1322,12 @@ fifo_expired:
 }
 
 /*
- * Add arq to a list behind alias
- */
-static inline void
-as_add_aliased_request(struct as_data *ad, struct as_rq *arq,
-                                struct as_rq *alias)
-{
-        struct request  *req = arq->request;
-        struct list_head *insert = alias->request->queuelist.prev;
-
-        /*
-         * Transfer list of aliases
-         */
-        while (!list_empty(&req->queuelist)) {
-                struct request *__rq = list_entry_rq(req->queuelist.next);
-                struct as_rq *__arq = RQ_DATA(__rq);
-
-                list_move_tail(&__rq->queuelist, &alias->request->queuelist);
-
-                WARN_ON(__arq->state != AS_RQ_QUEUED);
-        }
-
-        /*
-         * Another request with the same start sector on the rbtree.
-         * Link this request to that sector. They are untangled in
-         * as_move_to_dispatch
-         */
-        list_add(&arq->request->queuelist, insert);
-
-        /*
-         * Don't want to have to handle merges.
-         */
-        as_del_arq_hash(arq);
-        arq->request->flags |= REQ_NOMERGE;
-}
-
-/*
  * add arq to rbtree and fifo
  */
 static void as_add_request(request_queue_t *q, struct request *rq)
 {
         struct as_data *ad = q->elevator->elevator_data;
         struct as_rq *arq = RQ_DATA(rq);
-        struct as_rq *alias;
         int data_dir;
 
         arq->state = AS_RQ_NEW;
@@ -1387,33 +1346,17 @@ static void as_add_request(request_queue_t *q, struct request *rq)
                 atomic_inc(&arq->io_context->aic->nr_queued);
         }
 
-        alias = as_add_arq_rb(ad, arq);
-        if (!alias) {
-                /*
-                 * 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]);
+        as_add_arq_rb(ad, arq);
+        if (rq_mergeable(arq->request))
+                as_add_arq_hash(ad, arq);
 
-                if (rq_mergeable(arq->request))
-                        as_add_arq_hash(ad, arq);
-                as_update_arq(ad, arq); /* keep state machine up to date */
-
-        } else {
-                as_add_aliased_request(ad, arq, alias);
-
-                /*
-                 * 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);
-                }
-        }
+        /*
+         * 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]);
 
+        as_update_arq(ad, arq); /* keep state machine up to date */
         arq->state = AS_RQ_QUEUED;
 }
 
@@ -1536,23 +1479,8 @@ static void as_merged_request(request_queue_t *q, struct request *req)
          * if the merge was a front merge, we need to reposition request
          */
         if (rq_rb_key(req) != arq->rb_key) {
-                struct as_rq *alias, *next_arq = NULL;
-
-                if (ad->next_arq[arq->is_sync] == arq)
-                        next_arq = as_find_next_arq(ad, arq);
-
-                /*
-                 * Note! We should really be moving any old aliased requests
-                 * off this request and try to insert them into the rbtree. We
-                 * currently don't bother. Ditto the next function.
-                 */
                 as_del_arq_rb(ad, arq);
-                if ((alias = as_add_arq_rb(ad, arq))) {
-                        list_del_init(&arq->fifo);
-                        as_add_aliased_request(ad, arq, alias);
-                        if (next_arq)
-                                ad->next_arq[arq->is_sync] = next_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"
@@ -1579,18 +1507,8 @@ static void as_merged_requests(request_queue_t *q, struct request *req,
         as_add_arq_hash(ad, arq);
 
         if (rq_rb_key(req) != arq->rb_key) {
-                struct as_rq *alias, *next_arq = NULL;
-
-                if (ad->next_arq[arq->is_sync] == arq)
-                        next_arq = as_find_next_arq(ad, arq);
-
                 as_del_arq_rb(ad, arq);
-                if ((alias = as_add_arq_rb(ad, arq))) {
-                        list_del_init(&arq->fifo);
-                        as_add_aliased_request(ad, arq, alias);
-                        if (next_arq)
-                                ad->next_arq[arq->is_sync] = next_arq;
-                }
+                as_add_arq_rb(ad, arq);
         }
 
         /*
@@ -1610,18 +1528,6 @@ static void as_merged_requests(request_queue_t *q, struct request *req,
         }
 
         /*
-         * Transfer list of aliases
-         */
-        while (!list_empty(&next->queuelist)) {
-                struct request *__rq = list_entry_rq(next->queuelist.next);
-                struct as_rq *__arq = RQ_DATA(__rq);
-
-                list_move_tail(&__rq->queuelist, &req->queuelist);
-
-                WARN_ON(__arq->state != AS_RQ_QUEUED);
-        }
-
-        /*
          * kill knowledge of next, this one is a goner
          */
         as_remove_queued_request(q, next);