linux-kernel - Re: [PATCH V9 1/4] blk-mq: insert to hctx dispatch list when bypass

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Date:   Wed, 5 Dec 2018 09:25:45 -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 1/4] blk-mq: insert to hctx dispatch list when
 bypass_insert is true

On 12/5/18 12:43 AM, Jianchao Wang wrote:
> We don't allow direct dispatch of anything but regular reads/writes
> and insert all of non-read-write requests. However, this is not
> correct for 'bypass_insert == true' case where inserting is ignored
> and BLK_STS_RESOURCE is returned. The caller will fail forever.
> 
> Fix it with inserting the non-read-write request to hctx dispatch
> list to avoid to involve merge and io scheduler when bypass_insert
> is true.
> 
> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
> ---
>  block/blk-mq.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 9005505..153af90 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1822,6 +1822,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>  {
>  	struct request_queue *q = rq->q;
>  	bool run_queue = true;
> +	bool force = false;
>  
>  	/*
>  	 * RCU or SRCU read lock is needed before checking quiesced flag.
> @@ -1836,9 +1837,19 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>  		goto insert;
>  	}
>  
> -	if (!blk_rq_can_direct_dispatch(rq) || (q->elevator && !bypass_insert))
> +	if (q->elevator && !bypass_insert)
>  		goto insert;
>  
> +	if (!blk_rq_can_direct_dispatch(rq)) {
> +		/*
> +		 * For 'bypass_insert == true' case, insert request into hctx
> +		 * dispatch list.
> +		 */
> +		if (bypass_insert)
> +			force = true;
> +		goto insert;
> +	}

Just do force = bypass_insert, no need for the if.

-- 
Jens Axboe