> Il giorno 27 set 2022, alle ore 18:32, Paolo Valente <paolo.valente@xxxxxxxxxx> ha scritto:
>
>
>
>> Il giorno 16 set 2022, alle ore 09:19, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> ha scritto:
>>
>> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>>
>> Currently, bfq can't handle sync io concurrently as long as they
>> are not issued from root group. This is because
>> 'bfqd->num_groups_with_pending_reqs > 0' is always true in
>> bfq_asymmetric_scenario().
>>
>> The way that bfqg is counted into 'num_groups_with_pending_reqs':
>>
>> Before this patch:
>> 1) root group will never be counted.
>> 2) Count if bfqg or it's child bfqgs have pending requests.
>> 3) Don't count if bfqg and it's child bfqgs complete all the requests.
>>
>> After this patch:
>> 1) root group is counted.
>> 2) Count if bfqg have pending requests.
>> 3) Don't count if bfqg complete all the requests.
>>
>> With this change, the occasion that only one group is activated can be
>> detected, and next patch will support concurrent sync io in the
>> occasion.
>>
>> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
>> Reviewed-by: Jan Kara <jack@xxxxxxx>
>> ---
>> block/bfq-iosched.c | 42 ------------------------------------------
>> block/bfq-iosched.h | 18 +++++++++---------
>> block/bfq-wf2q.c | 23 ++++++++---------------
>> 3 files changed, 17 insertions(+), 66 deletions(-)
>>
>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>> index 0dcae2f52896..970b302a7a3e 100644
>> --- a/block/bfq-iosched.c
>> +++ b/block/bfq-iosched.c
>> @@ -970,48 +970,6 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd,
>> void bfq_weights_tree_remove(struct bfq_data *bfqd,
>> struct bfq_queue *bfqq)
>> {
>> - struct bfq_entity *entity = bfqq->entity.parent;
>> -
>> - 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, its parent entities are
>> - * active as well, and thus this loop must
>> - * stop here.
>> - */
>> - break;
>> - }
>> -
>> - /*
>> - * The decrement of num_groups_with_pending_reqs is
>> - * not performed immediately upon the deactivation of
>> - * entity, but it is delayed to when it also happens
>> - * that the first leaf descendant bfqq of entity gets
>> - * all its pending requests completed. The following
>> - * instructions perform this delayed decrement, if
>> - * needed. See the comments on
>> - * num_groups_with_pending_reqs for details.
>> - */
>> - if (entity->in_groups_with_pending_reqs) {
>> - entity->in_groups_with_pending_reqs = false;
>> - bfqd->num_groups_with_pending_reqs--;
>> - }
>> - }
>> -
>> - /*
>> - * Next function is invoked last, because it causes bfqq to be
>> - * freed if the following holds: bfqq is not in service and
>> - * has no dispatched request. DO NOT use bfqq after the next
>> - * function invocation.
>> - */
>> __bfq_weights_tree_remove(bfqd, bfqq,
>> &bfqd->queue_weights_tree);
>
> Why are you keeping the wrapper function bfq_weights_tree_remove() if it contains only the invocation of __bfq_weights_tree_remove()?
>
I had not seen patch 6/6, sorry.
Paolo
>> }
>> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
>> index 338ff5418ea8..257acb54c6dc 100644
>> --- a/block/bfq-iosched.h
>> +++ b/block/bfq-iosched.h
>> @@ -496,27 +496,27 @@ struct bfq_data {
>> struct rb_root_cached queue_weights_tree;
>>
>> /*
>> - * Number of groups with at least one descendant process that
>> + * Number of groups with at least one process that
>> * has at least one request waiting for completion. Note that
>> * this accounts for also requests already dispatched, but not
>> * yet completed. Therefore this number of groups may differ
>> * (be larger) than the number of active groups, as a group is
>> * considered active only if its corresponding entity has
>> - * descendant queues with at least one request queued. This
>> + * queues with at least one request queued. This
>> * number is used to decide whether a scenario is symmetric.
>> * For a detailed explanation see comments on the computation
>> * of the variable asymmetric_scenario in the function
>> * bfq_better_to_idle().
>> *
>> * However, it is hard to compute this number exactly, for
>> - * groups with multiple descendant processes. Consider a group
>> - * that is inactive, i.e., that has no descendant process with
>> + * groups with multiple processes. Consider a group
>> + * that is inactive, i.e., that has no process with
>> * pending I/O inside BFQ queues. Then suppose that
>> * num_groups_with_pending_reqs is still accounting for this
>> - * group, because the group has descendant processes with some
>> + * group, because the group has processes with some
>> * I/O request still in flight. num_groups_with_pending_reqs
>> * should be decremented when the in-flight request of the
>> - * last descendant process is finally completed (assuming that
>> + * last process is finally completed (assuming that
>> * nothing else has changed for the group in the meantime, in
>> * terms of composition of the group and active/inactive state of child
>> * groups and processes). To accomplish this, an additional
>> @@ -525,7 +525,7 @@ struct bfq_data {
>> * we resort to the following tradeoff between simplicity and
>> * accuracy: for an inactive group that is still counted in
>> * num_groups_with_pending_reqs, we decrement
>> - * num_groups_with_pending_reqs when the first descendant
>> + * num_groups_with_pending_reqs when the first
>> * process of the group remains with no request waiting for
>> * completion.
>> *
>> @@ -533,12 +533,12 @@ struct bfq_data {
>> * carefulness: to avoid multiple decrements, we flag a group,
>> * more precisely an entity representing a group, as still
>> * counted in num_groups_with_pending_reqs when it becomes
>> - * inactive. Then, when the first descendant queue of the
>> + * inactive. Then, when the first queue of the
>> * entity remains with no request waiting for completion,
>> * num_groups_with_pending_reqs is decremented, and this flag
>> * is reset. After this flag is reset for the entity,
>> * num_groups_with_pending_reqs won't be decremented any
>> - * longer in case a new descendant queue of the entity remains
>> + * longer in case a new queue of the entity remains
>> * with no request waiting for completion.
>> */
>> unsigned int num_groups_with_pending_reqs;
>> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
>> index 5549ccf09cd2..5e8224c96921 100644
>> --- a/block/bfq-wf2q.c
>> +++ b/block/bfq-wf2q.c
>> @@ -984,19 +984,6 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
>> entity->on_st_or_in_serv = true;
>> }
>>
>> -#ifdef CONFIG_BFQ_GROUP_IOSCHED
>> - if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
>> - struct bfq_group *bfqg =
>> - container_of(entity, struct bfq_group, entity);
>> - struct bfq_data *bfqd = bfqg->bfqd;
>> -
>> - if (!entity->in_groups_with_pending_reqs) {
>> - entity->in_groups_with_pending_reqs = true;
>> - bfqd->num_groups_with_pending_reqs++;
>> - }
>> - }
>> -#endif
>> -
>> bfq_update_fin_time_enqueue(entity, st, backshifted);
>> }
>>
>> @@ -1653,7 +1640,8 @@ void bfq_add_bfqq_in_groups_with_pending_reqs(struct bfq_queue *bfqq)
>> if (!entity->in_groups_with_pending_reqs) {
>> entity->in_groups_with_pending_reqs = true;
>> #ifdef CONFIG_BFQ_GROUP_IOSCHED
>> - bfqq_group(bfqq)->num_queues_with_pending_reqs++;
>> + if (!(bfqq_group(bfqq)->num_queues_with_pending_reqs++))
>> + bfqq->bfqd->num_groups_with_pending_reqs++;
>> #endif
>> }
>> }
>> @@ -1665,7 +1653,8 @@ void bfq_del_bfqq_in_groups_with_pending_reqs(struct bfq_queue *bfqq)
>> if (entity->in_groups_with_pending_reqs) {
>> entity->in_groups_with_pending_reqs = false;
>> #ifdef CONFIG_BFQ_GROUP_IOSCHED
>> - bfqq_group(bfqq)->num_queues_with_pending_reqs--;
>> + if (!(--bfqq_group(bfqq)->num_queues_with_pending_reqs))
>> + bfqq->bfqd->num_groups_with_pending_reqs--;
>> #endif
>> }
>> }
>> @@ -1694,6 +1683,10 @@ void bfq_del_bfqq_busy(struct bfq_queue *bfqq, bool expiration)
>>
>> if (!bfqq->dispatched) {
>> bfq_del_bfqq_in_groups_with_pending_reqs(bfqq);
>> + /*
>> + * Next function is invoked last, because it causes bfqq to be
>> + * freed. DO NOT use bfqq after the next function invocation.
>> + */
>
> Great, you moved this comment to the best place.
>
> Thanks,
> Paolo
>
>> bfq_weights_tree_remove(bfqd, bfqq);
>> }
>> }
>> --
>> 2.31.1
