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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 /block/bfq-iosched.h
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>
Diffstat (limited to 'block/bfq-iosched.h')
-rw-r--r--block/bfq-iosched.h7
1 files changed, 5 insertions, 2 deletions
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);