Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH V9 1/4] blk-mq: insert to hctx dispatch list when
 bypass_insert is true
To:     Jianchao Wang <jianchao.w.wang@oracle.com>
Cc:     ming.lei@redhat.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1543995842-20704-1-git-send-email-jianchao.w.wang@oracle.com>
 <1543995842-20704-2-git-send-email-jianchao.w.wang@oracle.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <54c7377f-e8e6-92cf-eced-6c76297afd52@kernel.dk>
Date:   Wed, 5 Dec 2018 09:25:45 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.2.1
MIME-Version: 1.0
In-Reply-To: <1543995842-20704-2-git-send-email-jianchao.w.wang@oracle.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@oracle.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