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Message-Id: <2968B663-F855-4C41-AE9B-E33787DA6AF9@linaro.org>
Date: Thu, 26 Aug 2021 19:00:53 +0200
From: Paolo Valente <paolo.valente@...aro.org>
To: Yu Kuai <yukuai3@...wei.com>
Cc: axboe@...nel.dk, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH v2 1/4] block, bfq: add support to track if root_group
have any pending requests
> Il giorno 6 ago 2021, alle ore 04:08, Yu Kuai <yukuai3@...wei.com> ha scritto:
>
> Add a new member in bfq_data to track number of queues that are in
> root_group with any pending requests.
maybe modify the last part of the sentence as: ... and that have some pending request
> This will be used in next patch
> to optmize queue idle judgment when root_group doesn't have any
> pending requests.
>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> block/bfq-iosched.c | 8 +++++++-
> block/bfq-iosched.h | 13 +++++++++++--
> block/bfq-wf2q.c | 37 ++++++++++++++++++++++++-------------
> 3 files changed, 42 insertions(+), 16 deletions(-)
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 727955918563..7c6b412f9a9c 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -859,8 +859,14 @@ 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;
> + struct bfq_entity *entity = &bfqq->entity;
> +
> + if (entity->in_groups_with_pending_reqs) {
> + entity->in_groups_with_pending_reqs = false;
> + bfqd->num_queues_with_pending_reqs_in_root--;
Here you cross the comment "The decrement of
num_groups_with_pending_reqs is not performed immediately upon ...".
Find a way to
- move that comment up, and to make it correct for this slightly
different decrement
- leave a correct comment (probably shorter) in the original position
> + }
>
> + entity = entity->parent;
> for_each_entity(entity) {
> struct bfq_sched_data *sd = entity->my_sched_data;
>
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 99c2a3cb081e..610769214f72 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -195,7 +195,12 @@ struct bfq_entity {
> /* flag, set to request a weight, ioprio or ioprio_class change */
> int prio_changed;
>
> - /* flag, set if the entity is counted in groups_with_pending_reqs */
> + /*
> + * If entity represents bfq_group, this flag will set
will be set?
> if the group is
> + * not root_group and have
has
> any pending requests; If entity represents
one more nit: use lowercase after semicolon
> + * bfq_queue, this flag will set
will be set
> if the queue is in root_group and have
> + * any pending requests.
> + */
> bool in_groups_with_pending_reqs;
>
The name of the above field follows from the fact that entity is
counted in groups_with_pending_reqs. You change this fact, because,
in your patch, a queue is not counted in groups_with_pending_reqs.
But you leave the same name. This creates confusion.
> /* last child queue of entity created (for non-leaf entities) */
> @@ -539,7 +544,11 @@ struct bfq_data {
> * with no request waiting for completion.
> */
> unsigned int num_groups_with_pending_reqs;
> -
> + /*
> + * number of queues that are in root_group with at least one request
> + * waiting for completion.
please link somehow this comment to the long comment that comes before it
> + */
> + unsigned int num_queues_with_pending_reqs_in_root;
Why using two counters? I mean, couldn't you simply count also the
root group in num_groups_with_pending_reqs?
> /*
> * Per-class (RT, BE, IDLE) number of bfq_queues containing
> * requests (including the queue in service, even if it is
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index 7a462df71f68..188c8f907219 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -946,6 +946,29 @@ static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
> bfq_active_insert(st, entity);
> }
>
> +static void bfq_update_groups_with_pending_reqs(struct bfq_entity *entity)
> +{
> +#ifdef CONFIG_BFQ_GROUP_IOSCHED
> + struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
> +
why do you introduce an extra variable bfqq, instead of doing as in
the original version of the code? In addition, you remove the comment
/* bfq_group */
Thanks,
Paolo
> + if (bfqq) {
> + if (!entity->parent && !entity->in_groups_with_pending_reqs) {
> + entity->in_groups_with_pending_reqs = true;
> + bfqq->bfqd->num_queues_with_pending_reqs_in_root++;
> + }
> + } else {
> + if (!entity->in_groups_with_pending_reqs) {
> + struct bfq_group *bfqg =
> + container_of(entity, struct bfq_group, entity);
> + struct bfq_data *bfqd = bfqg->bfqd;
> +
> + entity->in_groups_with_pending_reqs = true;
> + bfqd->num_groups_with_pending_reqs++;
> + }
> + }
> +#endif
> +}
> +
> /**
> * __bfq_activate_entity - handle activation of entity.
> * @entity: the entity being activated.
> @@ -999,19 +1022,7 @@ 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_groups_with_pending_reqs(entity);
> bfq_update_fin_time_enqueue(entity, st, backshifted);
> }
>
> --
> 2.31.1
>
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