linux-kernel - Re: [PATCH V5 2/6] blk-mq: refactor the code of issue request directly

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Date:   Mon, 12 Nov 2018 20:22:22 -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 V5 2/6] blk-mq: refactor the code of issue request
 directly

On 11/12/18 2:23 AM, Jianchao Wang wrote:
> Merge blk_mq_try_issue_directly and __blk_mq_try_issue_directly
> into one interface to unify the interfaces to issue requests
> directly. The merged interface takes over the requests totally,
> it could insert, end or do nothing based on the return value of
> .queue_rq and 'bypass' parameter. Then caller needn't any other
> handling any more.
> 
> To make code clearer, introduce new helpers enum mq_issue_decision
> and blk_mq_make_decision to decide how to handle the non-issued
> requests.
> 
> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
> ---
>  block/blk-mq.c | 108 +++++++++++++++++++++++++++++++++------------------------
>  1 file changed, 63 insertions(+), 45 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 364a53f..48b7a7c 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1766,77 +1766,95 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
>  	return ret;
>  }
>  
> -static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> +enum mq_issue_decision {
> +	MQ_ISSUE_INSERT_QUEUE,
> +	MQ_ISSUE_END_REQUEST,
> +	MQ_ISSUE_DO_NOTHING,
> +};
> +
> +static inline enum mq_issue_decision
> +	blk_mq_make_dicision(blk_status_t ret, bool bypass)
> +{
> +	enum mq_issue_decision dec;
> +
> +	switch(ret) {
> +	case BLK_STS_OK:
> +		dec = MQ_ISSUE_DO_NOTHING;
> +		break;
> +	case BLK_STS_DEV_RESOURCE:
> +	case BLK_STS_RESOURCE:
> +		dec = bypass ? MQ_ISSUE_DO_NOTHING : MQ_ISSUE_INSERT_QUEUE;
> +		break;
> +	default:
> +		dec = bypass ? MQ_ISSUE_DO_NOTHING : MQ_ISSUE_END_REQUEST;
> +		break;
> +	}
> +
> +	return dec;
> +}

You seem to mix and match decision and dicision, the former is the
right spelling.

But more importantly, not sure I like where this is going, wrapping
the return value in some other status code. That also makes it a bit
fragile in terms of adding other status codes, another spot to update.
Like the decent distinction between RESOURCE and DEV_RESOURCE.

Maybe it is cleaner to just handle this in the caller still?

-- 
Jens Axboe