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 <mpiazza@gmail.com> Reported-by: Laurentiu Nicola <lnicola@dend.ro> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Tested-by: Marco Piazza <mpiazza@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>hifive-unleashed-5.1
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7a69f9c60b
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431b17f9d5
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@ -3483,11 +3483,17 @@ static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
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}
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}
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}
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}
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}
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}
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/* Update weight both if it must be raised and if it must be lowered */
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/*
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* To improve latency (for this or other queues), immediately
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* update weight both if it must be raised and if it must be
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* lowered. Since, entity may be on some active tree here, and
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* might have a pending change of its ioprio class, invoke
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* next function with the last parameter unset (see the
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* comments on the function).
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*/
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if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
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if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
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__bfq_entity_update_weight_prio(
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__bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
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bfq_entity_service_tree(entity),
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entity, false);
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entity);
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}
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}
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/*
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/*
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@ -892,7 +892,8 @@ void bfq_put_idle_entity(struct bfq_service_tree *st,
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struct bfq_entity *entity);
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struct bfq_entity *entity);
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struct bfq_service_tree *
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struct bfq_service_tree *
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__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
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__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
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struct bfq_entity *entity);
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struct bfq_entity *entity,
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bool update_class_too);
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void bfq_bfqq_served(struct bfq_queue *bfqq, int served);
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void bfq_bfqq_served(struct bfq_queue *bfqq, int served);
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void bfq_bfqq_charge_time(struct bfq_data *bfqd, struct bfq_queue *bfqq,
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void bfq_bfqq_charge_time(struct bfq_data *bfqd, struct bfq_queue *bfqq,
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unsigned long time_ms);
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unsigned long time_ms);
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@ -694,10 +694,28 @@ struct bfq_service_tree *bfq_entity_service_tree(struct bfq_entity *entity)
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return sched_data->service_tree + idx;
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return sched_data->service_tree + idx;
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}
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}
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/*
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* Update weight and priority of entity. If update_class_too is true,
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* then update the ioprio_class of entity too.
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*
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* The reason why the update of ioprio_class is controlled through the
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* last parameter is as follows. Changing the ioprio class of an
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* entity implies changing the destination service trees for that
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* entity. If such a change occurred when the entity is already on one
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* of the service trees for its previous class, then the state of the
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* entity would become more complex: none of the new possible service
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* trees for the entity, according to bfq_entity_service_tree(), would
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* match any of the possible service trees on which the entity
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* is. Complex operations involving these trees, such as entity
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* activations and deactivations, should take into account this
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* additional complexity. To avoid this issue, this function is
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* invoked with update_class_too unset in the points in the code where
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* entity may happen to be on some tree.
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*/
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struct bfq_service_tree *
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struct bfq_service_tree *
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__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
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__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
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struct bfq_entity *entity)
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struct bfq_entity *entity,
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bool update_class_too)
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{
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{
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struct bfq_service_tree *new_st = old_st;
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struct bfq_service_tree *new_st = old_st;
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@ -739,9 +757,15 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
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bfq_weight_to_ioprio(entity->orig_weight);
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bfq_weight_to_ioprio(entity->orig_weight);
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}
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}
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if (bfqq)
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if (bfqq && update_class_too)
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bfqq->ioprio_class = bfqq->new_ioprio_class;
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bfqq->ioprio_class = bfqq->new_ioprio_class;
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entity->prio_changed = 0;
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/*
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* Reset prio_changed only if the ioprio_class change
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* is not pending any longer.
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*/
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if (!bfqq || bfqq->ioprio_class == bfqq->new_ioprio_class)
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entity->prio_changed = 0;
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/*
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/*
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* NOTE: here we may be changing the weight too early,
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* NOTE: here we may be changing the weight too early,
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@ -867,7 +891,12 @@ static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
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{
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{
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struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
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struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
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st = __bfq_entity_update_weight_prio(st, entity);
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/*
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* When this function is invoked, entity is not in any service
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* tree, then it is safe to invoke next function with the last
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* parameter set (see the comments on the function).
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*/
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st = __bfq_entity_update_weight_prio(st, entity, true);
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bfq_calc_finish(entity, entity->budget);
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bfq_calc_finish(entity, entity->budget);
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/*
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/*
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