linux-kernel - Re: [PATCH V9 3/4] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert

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Date:   Wed, 5 Dec 2018 09:30:44 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 3/4] blk-mq: issue directly with bypass 'false' in
 blk_mq_sched_insert_requests

On 12/5/18 12:44 AM, Jianchao Wang wrote:
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index fe92e52..0dfa269 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1899,32 +1899,23 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
>  void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
>  		struct list_head *list)
>  {
> +	blk_qc_t cookie = BLK_QC_T_INVALID;
> +

I'm fine with adding this, but I think we need some sort of check for
that not being a valid cookie. That isn't new, we really should have
already.

>  	while (!list_empty(list)) {
> -		blk_status_t ret;
>  		struct request *rq = list_first_entry(list, struct request,
>  				queuelist);
>  
> -		if (!blk_rq_can_direct_dispatch(rq))
> -			break;
> -
>  		list_del_init(&rq->queuelist);
> -		ret = blk_mq_request_issue_directly(rq, list_empty(list));
> -		if (ret != BLK_STS_OK) {
> -			if (ret == BLK_STS_RESOURCE ||
> -					ret == BLK_STS_DEV_RESOURCE) {
> -				list_add(&rq->queuelist, list);
> -				break;
> -			}
> -			blk_mq_end_request(rq, ret);
> -		}
> +		blk_mq_try_issue_directly(hctx, rq, &cookie, false,
> +				list_empty(list));

Indent the list_empty() one more tab, should be after the ( if possible.

> -	 * If we didn't flush the entire list, we could have told
> -	 * the driver there was more coming, but that turned out to
> -	 * be a lie.
> +	 * cookie is set to a valid value only when reqeust is issued successfully.
> +	 * We only need to care about the last request's result, if it is inserted,
> +	 * kick the hardware with commit_rqs hook.

reqeust -> request

Also lines are too long, limit to 80 chars please.

And why aren't we just using the list_empty() check like before, and not
having to add the inval cookie value?

> -	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs)
> +	if ((cookie == BLK_QC_T_INVALID) && hctx->queue->mq_ops->commit_rqs)
>  		hctx->queue->mq_ops->commit_rqs(hctx);

Redundant parens around the cookie check.

-- 
Jens Axboe