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authorPaolo Valente <paolo.valente@linaro.org>2018-06-25 21:55:34 +0200
committerJens Axboe <axboe@kernel.dk>2018-07-09 09:07:52 -0600
commit0471559c2fbd2c19d183fc0f51ce88aefa0a13c8 (patch)
tree5e8baa878335a2e1e8ac64648912d7b64d88c78c
parent6a5ac9846508ad7d1d23881d9d5add35f2e6ae71 (diff)
block, bfq: add/remove entity weights correctly
To keep I/O throughput high as often as possible, BFQ performs I/O-dispatch plugging (aka device idling) only when beneficial exactly for throughput, or when needed for service guarantees (low latency, fairness). An important case where the latter condition holds is when the scenario is 'asymmetric' in terms of weights: i.e., when some bfq_queue or whole group of queues has a higher weight, and thus has to receive more service, than other queues or groups. Without dispatch plugging, lower-weight queues/groups may unjustly steal bandwidth to higher-weight queues/groups. To detect asymmetric scenarios, BFQ checks some sufficient conditions. One of these conditions is that active groups have different weights. BFQ controls this condition by maintaining a special set of unique weights of active groups (group_weights_tree). To this purpose, in the function bfq_active_insert/bfq_active_extract BFQ adds/removes the weight of a group to/from this set. Unfortunately, the function bfq_active_extract may happen to be invoked also for a group that is still active (to preserve the correct update of the next queue to serve, see comments in function bfq_no_longer_next_in_service() for details). In this case, removing the weight of the group makes the set group_weights_tree inconsistent. Service-guarantee violations follow. This commit addresses this issue by moving group_weights_tree insertions from their previous location (in bfq_active_insert) into the function __bfq_activate_entity, and by moving group_weights_tree extractions from bfq_active_extract to when the entity that represents a group remains throughly idle, i.e., with no request either enqueued or dispatched. Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com> Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/bfq-iosched.c45
-rw-r--r--block/bfq-iosched.h7
-rw-r--r--block/bfq-wf2q.c24
3 files changed, 59 insertions, 17 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 495b9ddb3355..3f32e88c7e9b 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -742,8 +742,9 @@ inc_counter:
* See the comments to the function bfq_weights_tree_add() for considerations
* about overhead.
*/
-void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_entity *entity,
- struct rb_root *root)
+void __bfq_weights_tree_remove(struct bfq_data *bfqd,
+ struct bfq_entity *entity,
+ struct rb_root *root)
{
if (!entity->weight_counter)
return;
@@ -760,6 +761,43 @@ reset_entity_pointer:
}
/*
+ * Invoke __bfq_weights_tree_remove on bfqq and all its inactive
+ * parent entities.
+ */
+void bfq_weights_tree_remove(struct bfq_data *bfqd,
+ struct bfq_queue *bfqq)
+{
+ struct bfq_entity *entity = bfqq->entity.parent;
+
+ __bfq_weights_tree_remove(bfqd, &bfqq->entity,
+ &bfqd->queue_weights_tree);
+
+ for_each_entity(entity) {
+ struct bfq_sched_data *sd = entity->my_sched_data;
+
+ if (sd->next_in_service || sd->in_service_entity) {
+ /*
+ * entity is still active, because either
+ * next_in_service or in_service_entity is not
+ * NULL (see the comments on the definition of
+ * next_in_service for details on why
+ * in_service_entity must be checked too).
+ *
+ * As a consequence, the weight of entity is
+ * not to be removed. In addition, if entity
+ * is active, then its parent entities are
+ * active as well, and thus their weights are
+ * not to be removed either. In the end, this
+ * loop must stop here.
+ */
+ break;
+ }
+ __bfq_weights_tree_remove(bfqd, entity,
+ &bfqd->group_weights_tree);
+ }
+}
+
+/*
* Return expired entry, or NULL to just start from scratch in rbtree.
*/
static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
@@ -4582,8 +4620,7 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
*/
bfqq->budget_timeout = jiffies;
- bfq_weights_tree_remove(bfqd, &bfqq->entity,
- &bfqd->queue_weights_tree);
+ bfq_weights_tree_remove(bfqd, bfqq);
}
now_ns = ktime_get_ns();
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 0f712e03b035..a8a2e5aca4d4 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -827,8 +827,11 @@ struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic);
void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq);
void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_entity *entity,
struct rb_root *root);
-void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_entity *entity,
- struct rb_root *root);
+void __bfq_weights_tree_remove(struct bfq_data *bfqd,
+ struct bfq_entity *entity,
+ struct rb_root *root);
+void bfq_weights_tree_remove(struct bfq_data *bfqd,
+ struct bfq_queue *bfqq);
void bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bool compensate, enum bfqq_expiration reason);
void bfq_put_queue(struct bfq_queue *bfqq);
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 4498c43245e2..58cf38fcee05 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -499,9 +499,6 @@ static void bfq_active_insert(struct bfq_service_tree *st,
if (bfqq)
list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
- else /* bfq_group */
- bfq_weights_tree_add(bfqd, entity, &bfqd->group_weights_tree);
-
if (bfqg != bfqd->root_group)
bfqg->active_entities++;
#endif
@@ -601,10 +598,6 @@ static void bfq_active_extract(struct bfq_service_tree *st,
if (bfqq)
list_del(&bfqq->bfqq_list);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
- else /* bfq_group */
- bfq_weights_tree_remove(bfqd, entity,
- &bfqd->group_weights_tree);
-
if (bfqg != bfqd->root_group)
bfqg->active_entities--;
#endif
@@ -799,7 +792,7 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
if (prev_weight != new_weight) {
root = bfqq ? &bfqd->queue_weights_tree :
&bfqd->group_weights_tree;
- bfq_weights_tree_remove(bfqd, entity, root);
+ __bfq_weights_tree_remove(bfqd, entity, root);
}
entity->weight = new_weight;
/*
@@ -971,7 +964,7 @@ static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
* one of its children receives a new request.
*
* Basically, this function updates the timestamps of entity and
- * inserts entity into its active tree, ater possibly extracting it
+ * inserts entity into its active tree, after possibly extracting it
* from its idle tree.
*/
static void __bfq_activate_entity(struct bfq_entity *entity,
@@ -1015,6 +1008,16 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
entity->on_st = true;
}
+#ifdef BFQ_GROUP_IOSCHED_ENABLED
+ if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
+ struct bfq_group *bfqg =
+ container_of(entity, struct bfq_group, entity);
+
+ bfq_weights_tree_add(bfqg->bfqd, entity,
+ &bfqd->group_weights_tree);
+ }
+#endif
+
bfq_update_fin_time_enqueue(entity, st, backshifted);
}
@@ -1664,8 +1667,7 @@ void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfqd->busy_queues--;
if (!bfqq->dispatched)
- bfq_weights_tree_remove(bfqd, &bfqq->entity,
- &bfqd->queue_weights_tree);
+ bfq_weights_tree_remove(bfqd, bfqq);
if (bfqq->wr_coeff > 1)
bfqd->wr_busy_queues--;