[PATCH] deadline ioscheduler cleanups

Some various small cleanups, optimizations, and fixes.

o Make fifo_batch=32 as default, from testing this appears a good
  default value. We still get good throughput, and latency is good.

o Reintroduce the merge_cleanup logic. We need it for deadline for
  rehashing requests when they have been merged.

o Cleanup last_merge logic. Move it to the new elv_merged_request(),
  this is where it really belongs. Doing it inside the io scheduler core
  can causes false positives, when the queue merge functions reject an
  otherwise good merge

o Have deadline_move_requests() account from last entry on the dispatch
  queue, if it is non-empty. It doesn't really matter what the last
  extracted sector was, if we are not right behind it.

o Clean/optimize deadline_move_requests()

o Account size of a request just a little bit. Streaming transfer isn't
  for free, it's just a lot cheaper than a seek.

o Make deadline_check_fifo() more readable.

drivers/block/deadline-iosched.c

@@ -25,7 +25,7 @@
  * front fifo request expires.
  */
 static int read_expire = HZ / 2;	/* 500ms start timeout */
-static int fifo_batch = 64;		/* 4 seeks, or 64 contig */
+static int fifo_batch = 32;		/* 4 seeks, or 64 contig */
 static int seek_cost = 16;		/* seek is 16 times more expensive */
 
 /*
@@ -162,9 +162,8 @@ deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
 
 		if (elv_rq_merge_ok(__rq, bio)) {
 			*req = __rq;
-			q->last_merge = &__rq->queuelist;
 			ret = ELEVATOR_BACK_MERGE;
-			goto out_ret;
+			goto out;
 		}
 	}
 
@@ -191,23 +190,26 @@ deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
 			ret = elv_try_merge(__rq, bio);
 			if (ret != ELEVATOR_NO_MERGE) {
 				*req = __rq;
-				q->last_merge = &__rq->queuelist;
 				break;
 			}
 		}
 	}
 
 out:
-	if (ret != ELEVATOR_NO_MERGE) {
-		struct deadline_rq *drq = RQ_DATA(*req);
-
-		deadline_del_rq_hash(drq);
-		deadline_add_rq_hash(dd, drq);
-	}
-out_ret:
 	return ret;
 }
 
+static void deadline_merged_request(request_queue_t *q, struct request *req)
+{
+	struct deadline_data *dd = q->elevator.elevator_data;
+	struct deadline_rq *drq = RQ_DATA(req);
+
+	deadline_del_rq_hash(drq);
+	deadline_add_rq_hash(dd, drq);
+
+	q->last_merge = &req->queuelist;
+}
+
 static void
 deadline_merge_request(request_queue_t *q, struct request *req, struct request *next)
 {
@@ -255,8 +257,18 @@ static void deadline_move_requests(struct deadline_data *dd, struct request *rq)
 	sector_t last_sec = dd->last_sector;
 	int batch_count = dd->fifo_batch;
 
+	/*
+	 * if dispatch is non-empty, disregard last_sector and check last one
+	 */
+	if (!list_empty(dd->dispatch)) {
+		struct request *__rq = list_entry_rq(dd->dispatch->prev);
+
+		last_sec = __rq->sector + __rq->nr_sectors;
+	}
+
 	do {
 		struct list_head *nxt = rq->queuelist.next;
+		int this_rq_cost;
 
 		/*
 		 * take it off the sort and fifo list, move
@@ -264,17 +276,23 @@ static void deadline_move_requests(struct deadline_data *dd, struct request *rq)
 		 */
 		deadline_move_to_dispatch(dd, rq);
 
+		/*
+		 * if this is the last entry, don't bother doing accounting
+		 */
+		if (nxt == sort_head)
+			break;
+
+		this_rq_cost = dd->seek_cost;
 		if (rq->sector == last_sec)
-			batch_count--;
-		else
-			batch_count -= dd->seek_cost;
+			this_rq_cost = (rq->nr_sectors + 255) >> 8;
 
-		if (nxt == sort_head)
+		batch_count -= this_rq_cost;
+		if (batch_count <= 0)
 			break;
 
 		last_sec = rq->sector + rq->nr_sectors;
 		rq = list_entry_rq(nxt);
-	} while (batch_count > 0);
+	} while (1);
 }
 
 /*
@@ -283,16 +301,17 @@ static void deadline_move_requests(struct deadline_data *dd, struct request *rq)
 #define list_entry_fifo(ptr)	list_entry((ptr), struct deadline_rq, fifo)
 static inline int deadline_check_fifo(struct deadline_data *dd)
 {
-	struct deadline_rq *drq;
+	if (!list_empty(&dd->read_fifo)) {
+		struct deadline_rq *drq = list_entry_fifo(dd->read_fifo.next);
 
-	if (list_empty(&dd->read_fifo))
-		return 0;
-
-	drq = list_entry_fifo(dd->read_fifo.next);
-	if (time_before(jiffies, drq->expires))
-		return 0;
+		/*
+		 * drq is expired!
+		 */
+		if (time_after(jiffies, drq->expires))
+			return 1;
+	}
 
-	return 1;
+	return 0;
 }
 
 static struct request *deadline_next_request(request_queue_t *q)
@@ -411,8 +430,9 @@ static int deadline_queue_empty(request_queue_t *q)
 {
 	struct deadline_data *dd = q->elevator.elevator_data;
 
-	if (!list_empty(&q->queue_head) || !list_empty(&dd->sort_list[READ])
-	    || !list_empty(&dd->sort_list[WRITE]))
+	if (!list_empty(&dd->sort_list[WRITE]) ||
+	    !list_empty(&dd->sort_list[READ]) ||
+	    !list_empty(&q->queue_head))
 		return 0;
 
 	BUG_ON(!list_empty(&dd->read_fifo));
@@ -544,6 +564,7 @@ module_init(deadline_slab_setup);
 
 elevator_t iosched_deadline = {
 	.elevator_merge_fn = 		deadline_merge,
+	.elevator_merged_fn =		deadline_merged_request,
 	.elevator_merge_req_fn =	deadline_merge_request,
 	.elevator_next_req_fn =		deadline_next_request,
 	.elevator_add_req_fn =		deadline_add_request,

drivers/block/elevator.c

@@ -250,6 +250,14 @@ int elv_merge(request_queue_t *q, struct request **rq, struct bio *bio)
 	return ELEVATOR_NO_MERGE;
 }
 
+void elv_merged_request(request_queue_t *q, struct request *rq)
+{
+	elevator_t *e = &q->elevator;
+
+	if (e->elevator_merged_fn)
+		e->elevator_merged_fn(q, rq);
+}
+
 void elv_merge_requests(request_queue_t *q, struct request *rq,
 			     struct request *next)
 {

drivers/block/ll_rw_blk.c

@@ -1606,6 +1606,7 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 			req->biotail = bio;
 			req->nr_sectors = req->hard_nr_sectors += nr_sectors;
 			drive_stat_acct(req, nr_sectors, 0);
+			elv_merged_request(q, req);
 			attempt_back_merge(q, req);
 			goto out;
 
@@ -1629,6 +1630,7 @@ static int __make_request(request_queue_t *q, struct bio *bio)
 			req->sector = req->hard_sector = sector;
 			req->nr_sectors = req->hard_nr_sectors += nr_sectors;
 			drive_stat_acct(req, nr_sectors, 0);
+			elv_merged_request(q, req);
 			attempt_front_merge(q, req);
 			goto out;
 

include/linux/elevator.h

@@ -6,6 +6,8 @@ typedef int (elevator_merge_fn) (request_queue_t *, struct request **,
 
 typedef void (elevator_merge_req_fn) (request_queue_t *, struct request *, struct request *);
 
+typedef void (elevator_merged_fn) (request_queue_t *, struct request *);
+
 typedef struct request *(elevator_next_req_fn) (request_queue_t *);
 
 typedef void (elevator_add_req_fn) (request_queue_t *, struct request *, struct list_head *);
@@ -19,6 +21,7 @@ typedef void (elevator_exit_fn) (request_queue_t *, elevator_t *);
 struct elevator_s
 {
 	elevator_merge_fn *elevator_merge_fn;
+	elevator_merged_fn *elevator_merged_fn;
 	elevator_merge_req_fn *elevator_merge_req_fn;
 
 	elevator_next_req_fn *elevator_next_req_fn;
@@ -42,6 +45,7 @@ extern void __elv_add_request(request_queue_t *, struct request *,
 extern int elv_merge(request_queue_t *, struct request **, struct bio *);
 extern void elv_merge_requests(request_queue_t *, struct request *,
 			       struct request *);
+extern void elv_merged_request(request_queue_t *, struct request *);
 extern void elv_remove_request(request_queue_t *, struct request *);
 extern int elv_queue_empty(request_queue_t *);
 extern inline struct list_head *elv_get_sort_head(request_queue_t *, struct request *);