linux-kernel - Re: [PATCH V5 5/7] blk-mq-sched: move actual dispatching into one helper

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Date:   Mon, 2 Oct 2017 07:19:56 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...com>, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Laurence Oberman <loberman@...hat.com>,
        Paolo Valente <paolo.valente@...aro.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Tom Nguyen <tom81094@...il.com>, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Omar Sandoval <osandov@...com>
Subject: Re: [PATCH V5 5/7] blk-mq-sched: move actual dispatching into one
 helper

Can you move this to the beginning of your series, just after
the other edits to blk_mq_sched_dispatch_requests?

> +static void blk_mq_do_dispatch_sched(struct request_queue *q,
> +				     struct elevator_queue *e,
> +				     struct blk_mq_hw_ctx *hctx)

No need to pass anything but the hctx here, the other two can
be trivially derived from it.

> +{
> +	LIST_HEAD(rq_list);
> +
> +	do {
> +		struct request *rq;
> +
> +		rq = e->type->ops.mq.dispatch_request(hctx);

how about shortening this to:

	struct request *rq = e->type->ops.mq.dispatch_request(hctx);

>  void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
>  {
>  	struct request_queue *q = hctx->queue;
> @@ -136,16 +152,8 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
>  	 * on the dispatch list or we were able to dispatch from the
>  	 * dispatch list.
>  	 */
> -	if (do_sched_dispatch && has_sched_dispatch) {
> -		do {
> -			struct request *rq;
> -
> -			rq = e->type->ops.mq.dispatch_request(hctx);
> -			if (!rq)
> -				break;
> -			list_add(&rq->queuelist, &rq_list);
> -		} while (blk_mq_dispatch_rq_list(q, &rq_list));
> -	}
> +	if (do_sched_dispatch && has_sched_dispatch)
> +		blk_mq_do_dispatch_sched(q, e, hctx);
>  }

Please use this new helper to simplify the logic. E.g.:

	if (!list_empty(&rq_list)) {
		blk_mq_sched_mark_restart_hctx(hctx);
		if (blk_mq_dispatch_rq_list(q, &rq_list) && has_sched_dispatch)
			blk_mq_do_dispatch_sched(hctx);
	} else if (has_sched_dispatch) {
		blk_mq_do_dispatch_sched(hctx);
	} else {
		blk_mq_flush_busy_ctxs(hctx, &rq_list);
		blk_mq_dispatch_rq_list(q, &rq_list);
	}