dm: optimize dm_request_fn()

DM multipath is the only request-based DM target -- which only supports
tables with a single target that is immutable.  Leverage this fact in
dm_request_fn().

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 35ca9d065760e5cde3147518975abe16bfca5985..621450282d08933bdeba55087cda89939bc053fc 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2071,12 +2071,18 @@ static bool dm_request_peeked_before_merge_deadline(struct mapped_device *md)
 static void dm_request_fn(struct request_queue *q)
 {
        struct mapped_device *md = q->queuedata;
-       int srcu_idx;
-       struct dm_table *map = dm_get_live_table(md, &srcu_idx);
-       struct dm_target *ti;
+       struct dm_target *ti = md->immutable_target;
        struct request *rq;
        struct dm_rq_target_io *tio;
-       sector_t pos;
+       sector_t pos = 0;
+
+       if (unlikely(!ti)) {
+               int srcu_idx;
+               struct dm_table *map = dm_get_live_table(md, &srcu_idx);
+
+               ti = dm_table_find_target(map, pos);
+               dm_put_live_table(md, srcu_idx);
+       }
 
        /*
         * For suspend, check blk_queue_stopped() and increment
@@ -2087,33 +2093,21 @@ static void dm_request_fn(struct request_queue *q)
        while (!blk_queue_stopped(q)) {
                rq = blk_peek_request(q);
                if (!rq)
-                       goto out;
+                       return;
 
                /* always use block 0 to find the target for flushes for now */
                pos = 0;
                if (!(rq->cmd_flags & REQ_FLUSH))
                        pos = blk_rq_pos(rq);
 
-               ti = dm_table_find_target(map, pos);
-               if (!dm_target_is_valid(ti)) {
-                       /*
-                        * Must perform setup, that rq_completed() requires,
-                        * before calling dm_kill_unmapped_request
-                        */
-                       DMERR_LIMIT("request attempted access beyond the end of device");
-                       dm_start_request(md, rq);
-                       dm_kill_unmapped_request(rq, -EIO);
-                       continue;
+               if ((dm_request_peeked_before_merge_deadline(md) &&
+                    md_in_flight(md) && rq->bio && rq->bio->bi_vcnt == 1 &&
+                    md->last_rq_pos == pos && md->last_rq_rw == rq_data_dir(rq)) ||
+                   (ti->type->busy && ti->type->busy(ti))) {
+                       blk_delay_queue(q, HZ / 100);
+                       return;
                }
 
-               if (dm_request_peeked_before_merge_deadline(md) &&
-                   md_in_flight(md) && rq->bio && rq->bio->bi_vcnt == 1 &&
-                   md->last_rq_pos == pos && md->last_rq_rw == rq_data_dir(rq))
-                       goto delay_and_out;
-
-               if (ti->type->busy && ti->type->busy(ti))
-                       goto delay_and_out;
-
                dm_start_request(md, rq);
 
                tio = tio_from_request(rq);
@@ -2122,13 +2116,6 @@ static void dm_request_fn(struct request_queue *q)
                queue_kthread_work(&md->kworker, &tio->work);
                BUG_ON(!irqs_disabled());
        }
-
-       goto out;
-
-delay_and_out:
-       blk_delay_queue(q, HZ / 100);
-out:
-       dm_put_live_table(md, srcu_idx);
 }
 
 static int dm_any_congested(void *congested_data, int bdi_bits)