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block, bfq: consider also ioprio classes in symmetry detection

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In asymmetric scenarios, i.e., when some bfq_queue or bfq_group needs to
be guaranteed a different bandwidth than other bfq_queues or bfq_groups,
these service guaranteed can be provided only by plugging I/O dispatch,
completely or partially, when the queue in service remains temporarily
empty. A case where asymmetry is particularly strong is when some active
bfq_queues belong to a higher-priority class than some other active
bfq_queues. Unfortunately, this important case is not considered at all
in the code for detecting asymmetric scenarios. This commit adds the
missing logic.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Paolo Valente 2019-01-29 12:06:29 +01:00 committed by Jens Axboe
parent 03e565e420
commit 73d5811849
3 changed files with 59 additions and 47 deletions
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86
block/bfq-iosched.c
View File

@ -623,26 +623,6 @@ void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
bfqq->pos_root = NULL;
}
/*
* Tell whether there are active queues with different weights or
* active groups.
*/
static bool bfq_varied_queue_weights_or_active_groups(struct bfq_data *bfqd)
{
/*
* For queue weights to differ, queue_weights_tree must contain
* at least two nodes.
*/
return (!RB_EMPTY_ROOT(&bfqd->queue_weights_tree) &&
(bfqd->queue_weights_tree.rb_node->rb_left ||
bfqd->queue_weights_tree.rb_node->rb_right)
#ifdef CONFIG_BFQ_GROUP_IOSCHED
) ||
(bfqd->num_groups_with_pending_reqs > 0
#endif
);
}
/*
* The following function returns true if every queue must receive the
* same share of the throughput (this condition is used when deciding
@ -651,25 +631,48 @@ static bool bfq_varied_queue_weights_or_active_groups(struct bfq_data *bfqd)
*
* Such a scenario occurs when:
* 1) all active queues have the same weight,
* 2) all active groups at the same level in the groups tree have the same
* weight,
* 2) all active queues belong to the same I/O-priority class,
* 3) all active groups at the same level in the groups tree have the same
* weight,
* 4) all active groups at the same level in the groups tree have the same
* number of children.
*
* Unfortunately, keeping the necessary state for evaluating exactly
* the last two symmetry sub-conditions above would be quite complex
* and time consuming. Therefore this function evaluates, instead,
* only the following stronger two sub-conditions, for which it is
* and time consuming. Therefore this function evaluates, instead,
* only the following stronger three sub-conditions, for which it is
* much easier to maintain the needed state:
* 1) all active queues have the same weight,
* 2) there are no active groups.
* 2) all active queues belong to the same I/O-priority class,
* 3) there are no active groups.
* 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.
*/
static bool bfq_symmetric_scenario(struct bfq_data *bfqd)
{
return !bfq_varied_queue_weights_or_active_groups(bfqd);
/*
* For queue weights to differ, queue_weights_tree must contain
* at least two nodes.
*/
bool varied_queue_weights = !RB_EMPTY_ROOT(&bfqd->queue_weights_tree) &&
(bfqd->queue_weights_tree.rb_node->rb_left ||
bfqd->queue_weights_tree.rb_node->rb_right);
bool 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]);
/*
* For queue weights to differ, queue_weights_tree must contain
* at least two nodes.
*/
return !(varied_queue_weights || multiple_classes_busy
#ifdef BFQ_GROUP_IOSCHED_ENABLED
|| bfqd->num_groups_with_pending_reqs > 0
#endif
);
}
/*
@ -728,15 +731,14 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
/*
* In the unlucky event of an allocation failure, we just
* exit. This will cause the weight of queue to not be
* considered in bfq_varied_queue_weights_or_active_groups,
* which, in its turn, causes the scenario to be deemed
* wrongly symmetric in case bfqq's weight would have been
* the only weight making the scenario asymmetric. On the
* bright side, no unbalance will however occur when bfqq
* becomes inactive again (the invocation of this function
* is triggered by an activation of queue). In fact,
* bfq_weights_tree_remove does nothing if
* !bfqq->weight_counter.
* considered in bfq_symmetric_scenario, which, in its turn,
* causes the scenario to be deemed wrongly symmetric in case
* bfqq's weight would have been the only weight making the
* scenario asymmetric. On the bright side, no unbalance will
* however occur when bfqq becomes inactive again (the
* invocation of this function is triggered by an activation
* of queue). In fact, bfq_weights_tree_remove does nothing
* if !bfqq->weight_counter.
*/
if (unlikely(!bfqq->weight_counter))
return;
@ -2227,7 +2229,7 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
return NULL;
/* If there is only one backlogged queue, don't search. */
if (bfqd->busy_queues == 1)
if (bfq_tot_busy_queues(bfqd) == 1)
return NULL;
in_service_bfqq = bfqd->in_service_queue;
@ -3681,7 +3683,8 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq)
* the requests already queued in the device have been served.
*/
asymmetric_scenario = (bfqq->wr_coeff > 1 &&
bfqd->wr_busy_queues < bfqd->busy_queues) ||
bfqd->wr_busy_queues <
bfq_tot_busy_queues(bfqd)) ||
!bfq_symmetric_scenario(bfqd);
/*
@ -3960,7 +3963,7 @@ static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
* belongs to CLASS_IDLE and other queues are waiting for
* service.
*/
if (!(bfqd->busy_queues > 1 && bfq_class_idle(bfqq)))
if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq)))
goto return_rq;
bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
@ -3978,7 +3981,7 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
* most a call to dispatch for nothing
*/
return !list_empty_careful(&bfqd->dispatch) ||
bfqd->busy_queues > 0;
bfq_tot_busy_queues(bfqd) > 0;
}
static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
@ -4032,9 +4035,10 @@ static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
goto start_rq;
}
bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues);
bfq_log(bfqd, "dispatch requests: %d busy queues",
bfq_tot_busy_queues(bfqd));
if (bfqd->busy_queues == 0)
if (bfq_tot_busy_queues(bfqd) == 0)
goto exit;
/*

8
block/bfq-iosched.h
View File

@ -501,10 +501,11 @@ struct bfq_data {
unsigned int num_groups_with_pending_reqs;
/*
* Number of bfq_queues containing requests (including the
* queue in service, even if it is idling).
* Per-class (RT, BE, IDLE) number of bfq_queues containing
* requests (including the queue in service, even if it is
* idling).
*/
int busy_queues;
unsigned int busy_queues[3];
/* number of weight-raised busy @bfq_queues */
int wr_busy_queues;
/* number of queued requests */
@ -974,6 +975,7 @@ extern struct blkcg_policy blkcg_policy_bfq;
struct bfq_group *bfq_bfqq_to_bfqg(struct bfq_queue *bfqq);
struct bfq_queue *bfq_entity_to_bfqq(struct bfq_entity *entity);
unsigned int bfq_tot_busy_queues(struct bfq_data *bfqd);
struct bfq_service_tree *bfq_entity_service_tree(struct bfq_entity *entity);
struct bfq_entity *bfq_entity_of(struct rb_node *node);
unsigned short bfq_ioprio_to_weight(int ioprio);

12
block/bfq-wf2q.c
View File

@ -44,6 +44,12 @@ static unsigned int bfq_class_idx(struct bfq_entity *entity)
BFQ_DEFAULT_GRP_CLASS - 1;
}
unsigned int bfq_tot_busy_queues(struct bfq_data *bfqd)
{
return bfqd->busy_queues[0] + bfqd->busy_queues[1] +
bfqd->busy_queues[2];
}
static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
bool expiration);
@ -1513,7 +1519,7 @@ struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd)
struct bfq_sched_data *sd;
struct bfq_queue *bfqq;
if (bfqd->busy_queues == 0)
if (bfq_tot_busy_queues(bfqd) == 0)
return NULL;
/*
@ -1665,7 +1671,7 @@ void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfq_clear_bfqq_busy(bfqq);
bfqd->busy_queues--;
bfqd->busy_queues[bfqq->ioprio_class - 1]--;
if (!bfqq->dispatched)
bfq_weights_tree_remove(bfqd, bfqq);
@ -1688,7 +1694,7 @@ void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
bfq_activate_bfqq(bfqd, bfqq);
bfq_mark_bfqq_busy(bfqq);
bfqd->busy_queues++;
bfqd->busy_queues[bfqq->ioprio_class - 1]++;
if (!bfqq->dispatched)
if (bfqq->wr_coeff == 1)