diff mbox series

[V9,2/8] block, bfq: forbid stable merging of queues associated with different actuators

Message ID 20221208104351.35038-3-paolo.valente@linaro.org (mailing list archive)
State New, archived
Headers show
Series block, bfq: extend bfq to support multi-actuator drives | expand

Commit Message

Paolo Valente Dec. 8, 2022, 10:43 a.m. UTC 
If queues associated with different actuators are merged, then control
is lost on each actuator. Therefore some actuator may be
underutilized, and throughput may decrease. This problem cannot occur
with basic queue merging, because the latter is triggered by spatial
locality, and sectors for different actuators are not close to each
other. Yet it may happen with stable merging. To address this issue,
this commit prevents stable merging from occurring among queues
associated with different actuators.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
 block/bfq-iosched.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 16dbf52ce74b..456b5f5c24fd 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5708,9 +5708,13 @@  static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
 	 * it has been set already, but too long ago, then move it
 	 * forward to bfqq. Finally, move also if bfqq belongs to a
 	 * different group than last_bfqq_created, or if bfqq has a
-	 * different ioprio or ioprio_class. If none of these
-	 * conditions holds true, then try an early stable merge or
-	 * schedule a delayed stable merge.
+	 * different ioprio, ioprio_class or actuator_idx. If none of
+	 * these conditions holds true, then try an early stable merge
+	 * or schedule a delayed stable merge. As for the condition on
+	 * actuator_idx, the reason is that, if queues associated with
+	 * different actuators are merged, then control is lost on
+	 * each actuator. Therefore some actuator may be
+	 * underutilized, and throughput may decrease.
 	 *
 	 * A delayed merge is scheduled (instead of performing an
 	 * early merge), in case bfqq might soon prove to be more
@@ -5728,7 +5732,8 @@  static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
 			bfqq->creation_time) ||
 		bfqq->entity.parent != last_bfqq_created->entity.parent ||
 		bfqq->ioprio != last_bfqq_created->ioprio ||
-		bfqq->ioprio_class != last_bfqq_created->ioprio_class)
+		bfqq->ioprio_class != last_bfqq_created->ioprio_class ||
+		bfqq->actuator_idx != last_bfqq_created->actuator_idx)
 		*source_bfqq = bfqq;
 	else if (time_after_eq(last_bfqq_created->creation_time +
 				 bfqd->bfq_burst_interval,