path: root/block/bfq-iosched.c
diff options
authorPaolo Valente <>2017-07-03 10:00:10 +0200
committerJens Axboe <>2017-07-03 16:50:00 -0600
commit431b17f9d5453533cba7d73e7e40428e4f90b35d (patch)
treee42cf25bcbfbc315f6b4fc3660dce0890cfdbbe2 /block/bfq-iosched.c
parent7a69f9c60b49699579f5bfb71f928cceba0afe1a (diff)
block, bfq: don't change ioprio class for a bfq_queue on a service tree
On each deactivation or re-scheduling (after being served) of a bfq_queue, BFQ invokes the function __bfq_entity_update_weight_prio(), to perform pending updates of ioprio, weight and ioprio class for the bfq_queue. BFQ also invokes this function on I/O-request dispatches, to raise or lower weights more quickly when needed, thereby improving latency. However, the entity representing the bfq_queue may be on the active (sub)tree of a service tree when this happens, and, although with a very low probability, the bfq_queue may happen to also have a pending change of its ioprio class. If both conditions hold when __bfq_entity_update_weight_prio() is invoked, then the entity moves to a sort of hybrid state: the new service tree for the entity, as returned by bfq_entity_service_tree(), differs from service tree on which the entity still is. The functions that handle activations and deactivations of entities do not cope with such a hybrid state (and would need to become more complex to cope). This commit addresses this issue by just making __bfq_entity_update_weight_prio() not perform also a possible pending change of ioprio class, when invoked on an I/O-request dispatch for a bfq_queue. Such a change is thus postponed to when __bfq_entity_update_weight_prio() is invoked on deactivation or re-scheduling of the bfq_queue. Reported-by: Marco Piazza <> Reported-by: Laurentiu Nicola <> Signed-off-by: Paolo Valente <> Tested-by: Marco Piazza <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block/bfq-iosched.c')
1 files changed, 10 insertions, 4 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 12bbc6b..60a6835 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -3483,11 +3483,17 @@ static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
- /* Update weight both if it must be raised and if it must be lowered */
+ /*
+ * To improve latency (for this or other queues), immediately
+ * update weight both if it must be raised and if it must be
+ * lowered. Since, entity may be on some active tree here, and
+ * might have a pending change of its ioprio class, invoke
+ * next function with the last parameter unset (see the
+ * comments on the function).
+ */
if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
- __bfq_entity_update_weight_prio(
- bfq_entity_service_tree(entity),
- entity);
+ __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
+ entity, false);