Re: [PATCH 07/14] blk-mq: support multiple hctx maps

[Bart Van Assche <bvanassche@acm.org>]

On Mon, 2018-10-29 at 10:37 -0600, Jens Axboe wrote:
> -static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
> -						     unsigned int flags,
> -						     int cpu)
> +static inline struct blk_mq_hw_ctx *blk_mq_map_queue_type(struct request_queue *q,
> +							  int type, int cpu)
>  {
>  	struct blk_mq_tag_set *set = q->tag_set;
>  
> -	return q->queue_hw_ctx[set->map[0].mq_map[cpu]];
> +	return q->queue_hw_ctx[set->map[type].mq_map[cpu]];
>  }
>  
> -static inline struct blk_mq_hw_ctx *blk_mq_map_queue_type(struct request_queue *q,
> -							  int type, int cpu)
> +static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
> +						     unsigned int flags,
> +						     int cpu)
>  {
> -	return blk_mq_map_queue(q, type, cpu);
> +	int type = 0;
> +
> +	if (q->mq_ops->flags_to_type)
> +		type = q->mq_ops->flags_to_type(q, flags);
> +
> +	return blk_mq_map_queue_type(q, type, cpu);
>  }

How about adding a comment above both these functions that explains their
purpose? Since blk_mq_map_queue() maps rq->cmd_flags and the cpu index to
a hardware context, how about renaming blk_mq_map_queue() into
blk_mq_map_cmd_flags()?

>  /*
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index f9e19962a22f..837087cf07cc 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -86,6 +86,7 @@ enum {
>  
>  struct blk_mq_tag_set {
>  	struct blk_mq_queue_map	map[HCTX_MAX_TYPES];
> +	unsigned int		nr_maps;
>  	const struct blk_mq_ops	*ops;
>  	unsigned int		nr_hw_queues;
>  	unsigned int		queue_depth;	/* max hw supported */
> @@ -109,6 +110,7 @@ struct blk_mq_queue_data {
>  
>  typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *,
>  		const struct blk_mq_queue_data *);
> +typedef int (flags_to_type_fn)(struct request_queue *, unsigned int);

How about adding a comment that the format of the second argument of
flags_to_type_fn is the same as that of rq->cmd_flags?

Thanks,

Bart.