dm: optimize dm_mq_queue_rq()
DM multipath is the only dm-mq target. But that aside, request-based DM
only supports tables with a single target that is immutable. Leverage
this fact in dm_mq_queue_rq() by using the 'immutable_target' stored in
the mapped_device when the table was made active. This saves the need
to even take the read-side of the SRCU via dm_{get,put}_live_table.
If the active DM table does not have an immutable target (e.g. "error"
target was swapped in) then fallback to the slow-path where the target
is looked up from the live table.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index cfa29f5..3ddaa11 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1684,7 +1684,8 @@
*---------------------------------------------------------------*/
static struct target_type multipath_target = {
.name = "multipath",
- .version = {1, 10, 0},
+ .version = {1, 11, 0},
+ .features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE,
.module = THIS_MODULE,
.ctr = multipath_ctr,
.dtr = multipath_dtr,
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index a49e62b..89180fd 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -920,6 +920,16 @@
return t->immutable_target_type;
}
+struct dm_target *dm_table_get_immutable_target(struct dm_table *t)
+{
+ /* Immutable target is implicitly a singleton */
+ if (t->num_targets > 1 ||
+ !dm_target_is_immutable(t->targets[0].type))
+ return NULL;
+
+ return t->targets;
+}
+
struct dm_target *dm_table_get_wildcard_target(struct dm_table *t)
{
struct dm_target *uninitialized_var(ti);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index d605170..35ca9d0 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -154,6 +154,7 @@
/* Protect queue and type against concurrent access. */
struct mutex type_lock;
+ struct dm_target *immutable_target;
struct target_type *immutable_target_type;
struct gendisk *disk;
@@ -2492,8 +2493,15 @@
* This must be done before setting the queue restrictions,
* because request-based dm may be run just after the setting.
*/
- if (dm_table_request_based(t))
+ if (dm_table_request_based(t)) {
stop_queue(q);
+ /*
+ * Leverage the fact that request-based DM targets are
+ * immutable singletons and establish md->immutable_target
+ * - used to optimize both dm_request_fn and dm_mq_queue_rq
+ */
+ md->immutable_target = dm_table_get_immutable_target(t);
+ }
__bind_mempools(md, t);
@@ -2564,7 +2572,6 @@
unsigned dm_get_md_type(struct mapped_device *md)
{
- BUG_ON(!mutex_is_locked(&md->type_lock));
return md->type;
}
@@ -2641,28 +2648,15 @@
struct request *rq = bd->rq;
struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);
struct mapped_device *md = tio->md;
- int srcu_idx;
- struct dm_table *map = dm_get_live_table(md, &srcu_idx);
- struct dm_target *ti;
- sector_t pos;
+ struct dm_target *ti = md->immutable_target;
- /* 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);
+ if (unlikely(!ti)) {
+ int srcu_idx;
+ struct dm_table *map = dm_get_live_table(md, &srcu_idx);
- ti = dm_table_find_target(map, pos);
- if (!dm_target_is_valid(ti)) {
+ ti = dm_table_find_target(map, 0);
dm_put_live_table(md, srcu_idx);
- DMERR_LIMIT("request attempted access beyond the end of device");
- /*
- * Must perform setup, that rq_completed() requires,
- * before returning BLK_MQ_RQ_QUEUE_ERROR
- */
- dm_start_request(md, rq);
- return BLK_MQ_RQ_QUEUE_ERROR;
}
- dm_put_live_table(md, srcu_idx);
if (ti->type->busy && ti->type->busy(ti))
return BLK_MQ_RQ_QUEUE_BUSY;
@@ -2678,8 +2672,10 @@
*/
tio->ti = ti;
- /* Clone the request if underlying devices aren't blk-mq */
- if (dm_table_get_type(map) == DM_TYPE_REQUEST_BASED) {
+ /*
+ * Both the table and md type cannot change after initial table load
+ */
+ if (dm_get_md_type(md) == DM_TYPE_REQUEST_BASED) {
/* clone request is allocated at the end of the pdu */
tio->clone = (void *)blk_mq_rq_to_pdu(rq) + sizeof(struct dm_rq_target_io);
(void) clone_rq(rq, md, tio, GFP_ATOMIC);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 53df258..4305a51 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -73,6 +73,7 @@
int dm_table_any_congested(struct dm_table *t, int bdi_bits);
unsigned dm_table_get_type(struct dm_table *t);
struct target_type *dm_table_get_immutable_target_type(struct dm_table *t);
+struct dm_target *dm_table_get_immutable_target(struct dm_table *t);
struct dm_target *dm_table_get_wildcard_target(struct dm_table *t);
bool dm_table_request_based(struct dm_table *t);
bool dm_table_mq_request_based(struct dm_table *t);