If only one group is activated, there is no need to guarantee the same
share of the throughput of queues in the same group.
If CONFIG_BFQ_GROUP_IOSCHED is enabled, there is no need to check
'varied_queue_weights' and 'multiple_classes_busy':
1) num_groups_with_pending_reqs = 0, idle is not needed
2) num_groups_with_pending_reqs = 1
- if root group have any pending requests, idle is needed
- if root group is idle, idle is not needed
3) num_groups_with_pending_reqs > 1, idle is needed
Test procedure:
run "fio -numjobs=1 -ioengine=psync -bs=4k -direct=1 -rw=randread..."
multiple times in the same cgroup(not root).
Test result: total bandwidth(Mib/s)
| total jobs | before this patch | after this patch |
| ---------- | ----------------- | --------------------- |
| 1 | 33.8 | 33.8 |
| 2 | 33.8 | 65.4 (32.7 each job) |
| 4 | 33.8 | 106.8 (26.7 each job) |
| 8 | 33.8 | 126.4 (15.8 each job) |
By the way, if I test with "fio -numjobs=1/2/4/8 ...", test result is
the same with or without this patch.
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/bfq-iosched.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7c6b412f9a9c..a780205a1be4 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -709,7 +709,9 @@ bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
* much easier to maintain the needed state:
* 1) all active queues have the same weight,
* 2) all active queues belong to the same I/O-priority class,
- * 3) there are no active groups.
+ * 3) there are one active group at most(incluing root_group).
+ * If the last condition is false, there is no need to guarantee the,
+ * same share of the throughput of queues in the same group.
* In particular, the last condition is always true if hierarchical
* support or the cgroups interface are not enabled, thus no state
* needs to be maintained in this case.
@@ -717,7 +719,26 @@ bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
struct bfq_queue *bfqq)
{
- bool smallest_weight = bfqq &&
+ bool smallest_weight;
+ bool varied_queue_weights;
+ bool multiple_classes_busy;
+
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+ if (bfqd->num_groups_with_pending_reqs > 1)
+ return true;
+
+ if (bfqd->num_groups_with_pending_reqs &&
+ bfqd->num_queues_with_pending_reqs_in_root)
+ return true;
+
+ /*
+ * Reach here means only one group(incluing root group) has pending
+ * requests, thus it's safe to return.
+ */
+ return false;
+#endif
+
+ smallest_weight = bfqq &&
bfqq->weight_counter &&
bfqq->weight_counter ==
container_of(
@@ -729,21 +750,17 @@ static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
* For queue weights to differ, queue_weights_tree must contain
* at least two nodes.
*/
- bool varied_queue_weights = !smallest_weight &&
+ varied_queue_weights = !smallest_weight &&
!RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
(bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
- bool multiple_classes_busy =
+ multiple_classes_busy =
(bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
(bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
(bfqd->busy_queues[1] && bfqd->busy_queues[2]);
- return varied_queue_weights || multiple_classes_busy
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
- || bfqd->num_groups_with_pending_reqs > 0
-#endif
- ;
+ return varied_queue_weights || multiple_classes_busy;
}
/*
--
2.31.1
