linux-kernel - Re: [PATCH -next v2 2/5] block, bfq: add fake weight

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Date:   Mon, 25 Apr 2022 11:48:56 +0200
From:   Jan Kara <jack@...e.cz>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     jack@...e.cz, paolo.valente@...aro.org, axboe@...nel.dk,
        tj@...nel.org, linux-block@...r.kernel.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next v2 2/5] block, bfq: add fake weight_counter for
 weight-raised queue

On Sat 16-04-22 17:37:50, Yu Kuai wrote:
> Weight-raised queue is not inserted to weights_tree, which makes it
> impossible to track how many queues have pending requests through
> weights_tree insertion and removel. This patch add fake weight_counter
> for weight-raised queue to do that.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

This is a bit hacky. I was looking into a better place where to hook to
count entities in a bfq_group with requests and I think bfq_add_bfqq_busy()
and bfq_del_bfqq_busy() are ideal for this. It also makes better sense
conceptually than hooking into weights tree handling.

Other than this the rest of the series looks fine to me.

								Honza

> ---
>  block/bfq-iosched.c | 11 +++++++++++
>  block/bfq-wf2q.c    |  5 ++---
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 2deea2d07a1f..a2977c938c70 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -134,6 +134,8 @@
>  #include "bfq-iosched.h"
>  #include "blk-wbt.h"
>  
> +#define BFQ_FAKE_WEIGHT_COUNTER ((void *) POISON_INUSE)
> +
>  #define BFQ_BFQQ_FNS(name)						\
>  void bfq_mark_bfqq_##name(struct bfq_queue *bfqq)			\
>  {									\
> @@ -884,6 +886,12 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq)
>  	if (bfqq->weight_counter)
>  		return;
>  
> +	if (bfqq->wr_coeff != 1) {
> +		bfqq->weight_counter = BFQ_FAKE_WEIGHT_COUNTER;
> +		bfqq->ref++;
> +		return;
> +	}
> +
>  	while (*new) {
>  		struct bfq_weight_counter *__counter = container_of(*new,
>  						struct bfq_weight_counter,
> @@ -943,6 +951,9 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_queue *bfqq)
>  	if (!bfqq->weight_counter)
>  		return;
>  
> +	if (bfqq->weight_counter == BFQ_FAKE_WEIGHT_COUNTER)
> +		goto reset_entity_pointer;
> +
>  	root = &bfqd->queue_weights_tree;
>  	bfqq->weight_counter->num_active--;
>  	if (bfqq->weight_counter->num_active > 0)
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index a1296058c1ec..ae12c6b2c525 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -776,7 +776,7 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
>  		 * Add the entity, if it is not a weight-raised queue,
>  		 * to the counter associated with its new weight.
>  		 */
> -		if (prev_weight != new_weight && bfqq && bfqq->wr_coeff == 1)
> +		if (prev_weight != new_weight && bfqq)
>  			bfq_weights_tree_add(bfqd, bfqq);
>  
>  		new_st->wsum += entity->weight;
> @@ -1680,8 +1680,7 @@ void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
>  	bfqd->busy_queues[bfqq->ioprio_class - 1]++;
>  
>  	if (!bfqq->dispatched)
> -		if (bfqq->wr_coeff == 1)
> -			bfq_weights_tree_add(bfqd, bfqq);
> +		bfq_weights_tree_add(bfqd, bfqq);
>  
>  	if (bfqq->wr_coeff > 1)
>  		bfqd->wr_busy_queues++;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR