Re: [PATCH 6/8] blk-ioprio: Convert from rqos policy to direct call

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 6/16/22 01:16, Jan Kara wrote:
> Convert blk-ioprio handling from a rqos policy to a direct call from
> blk_mq_submit_bio(). Firstly, blk-ioprio is not a much of a rqos policy
> anyway, it just needs a hook in bio submission path to set the bio's IO
> priority. Secondly, the rqos .track hook gets actually called too late
> for blk-ioprio purposes and introducing a special rqos hook just for
> blk-ioprio looks even weirder.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>   block/blk-cgroup.c |  1 +
>   block/blk-ioprio.c | 50 +++++-----------------------------------------
>   block/blk-ioprio.h |  9 +++++++++
>   block/blk-mq.c     |  8 ++++++++
>   4 files changed, 23 insertions(+), 45 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 764e740b0c0f..6906981563f8 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -1299,6 +1299,7 @@ int blkcg_init_queue(struct request_queue *q)
>   	ret = blk_iolatency_init(q);
>   	if (ret) {
>   		blk_throtl_exit(q);
> +		blk_ioprio_exit(q);
>   		goto err_destroy_all;
>   	}
>   
> diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
> index 3f605583598b..c00060a02c6e 100644
> --- a/block/blk-ioprio.c
> +++ b/block/blk-ioprio.c
> @@ -181,17 +181,12 @@ static struct blkcg_policy ioprio_policy = {
>   	.pd_free_fn	= ioprio_free_pd,
>   };
>   
> -struct blk_ioprio {
> -	struct rq_qos rqos;
> -};
> -
> -static void blkcg_ioprio_track(struct rq_qos *rqos, struct request *rq,
> -			       struct bio *bio)
> +void blkcg_set_ioprio(struct bio *bio)
>   {
>   	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
>   	u16 prio;
>   
> -	if (blkcg->prio_policy == POLICY_NO_CHANGE)
> +	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)

See my comment on patch 8.

>   		return;
>   
>   	/*
> @@ -207,49 +202,14 @@ static void blkcg_ioprio_track(struct rq_qos *rqos, struct request *rq,
>   		bio->bi_ioprio = prio;
>   }
>   
> -static void blkcg_ioprio_exit(struct rq_qos *rqos)
> +void blk_ioprio_exit(struct request_queue *q)
>   {
> -	struct blk_ioprio *blkioprio_blkg =
> -		container_of(rqos, typeof(*blkioprio_blkg), rqos);
> -
> -	blkcg_deactivate_policy(rqos->q, &ioprio_policy);
> -	kfree(blkioprio_blkg);
> +	blkcg_deactivate_policy(q, &ioprio_policy);
>   }
>   
> -static struct rq_qos_ops blkcg_ioprio_ops = {
> -	.track	= blkcg_ioprio_track,
> -	.exit	= blkcg_ioprio_exit,
> -};
> -
>   int blk_ioprio_init(struct request_queue *q)
>   {
> -	struct blk_ioprio *blkioprio_blkg;
> -	struct rq_qos *rqos;
> -	int ret;
> -
> -	blkioprio_blkg = kzalloc(sizeof(*blkioprio_blkg), GFP_KERNEL);
> -	if (!blkioprio_blkg)
> -		return -ENOMEM;
> -
> -	ret = blkcg_activate_policy(q, &ioprio_policy);
> -	if (ret) {
> -		kfree(blkioprio_blkg);
> -		return ret;
> -	}
> -
> -	rqos = &blkioprio_blkg->rqos;
> -	rqos->id = RQ_QOS_IOPRIO;
> -	rqos->ops = &blkcg_ioprio_ops;
> -	rqos->q = q;
> -
> -	/*
> -	 * Registering the rq-qos policy after activating the blk-cgroup
> -	 * policy guarantees that ioprio_blkcg_from_bio(bio) != NULL in the
> -	 * rq-qos callbacks.
> -	 */
> -	rq_qos_add(q, rqos);
> -
> -	return 0;
> +	return blkcg_activate_policy(q, &ioprio_policy);
>   }
>   
>   static int __init ioprio_init(void)
> diff --git a/block/blk-ioprio.h b/block/blk-ioprio.h
> index a7785c2f1aea..5a1eb550e178 100644
> --- a/block/blk-ioprio.h
> +++ b/block/blk-ioprio.h
> @@ -6,14 +6,23 @@
>   #include <linux/kconfig.h>
>   
>   struct request_queue;
> +struct bio;
>   
>   #ifdef CONFIG_BLK_CGROUP_IOPRIO
>   int blk_ioprio_init(struct request_queue *q);
> +void blk_ioprio_exit(struct request_queue *q);
> +void blkcg_set_ioprio(struct bio *bio);
>   #else
>   static inline int blk_ioprio_init(struct request_queue *q)
>   {
>   	return 0;
>   }
> +static inline void blk_ioprio_exit(struct request_queue *q)
> +{
> +}
> +static inline void blkcg_set_ioprio(struct bio *bio)
> +{
> +}
>   #endif
>   
>   #endif /* _BLK_IOPRIO_H_ */
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index e9bf950983c7..67a7bfa58b7c 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -42,6 +42,7 @@
>   #include "blk-stat.h"
>   #include "blk-mq-sched.h"
>   #include "blk-rq-qos.h"
> +#include "blk-ioprio.h"
>   
>   static DEFINE_PER_CPU(struct llist_head, blk_cpu_done);
>   
> @@ -2790,6 +2791,11 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
>   	return rq;
>   }
>   
> +static void bio_set_ioprio(struct bio *bio)
> +{
> +	blkcg_set_ioprio(bio);
> +}
> +
>   /**
>    * blk_mq_submit_bio - Create and send a request to block device.
>    * @bio: Bio pointer.
> @@ -2830,6 +2836,8 @@ void blk_mq_submit_bio(struct bio *bio)
>   
>   	trace_block_getrq(bio);
>   
> +	bio_set_ioprio(bio);
> +
>   	rq_qos_track(q, rq, bio);
>   
>   	blk_mq_bio_to_request(rq, bio, nr_segs);


-- 
Damien Le Moal
Western Digital Research