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Date:   Thu, 6 Dec 2018 20:34:35 -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 V11 0/4] blk-mq: refactor code of issue directly

On 12/6/18 8:32 PM, Jens Axboe wrote:
> On 12/6/18 8:26 PM, jianchao.wang wrote:
>>
>>
>> On 12/7/18 11:16 AM, Jens Axboe wrote:
>>> On 12/6/18 8:09 PM, Jianchao Wang wrote:
>>>> Hi Jens
>>>>
>>>> Please consider this patchset for 4.21.
>>>>
>>>> It refactors the code of issue request directly to unify the interface
>>>> and make the code clearer and more readable.
>>>>
>>>> This patch set is rebased on the recent for-4.21/block and add the 1st
>>>> patch which inserts the non-read-write request to hctx dispatch
>>>> list to avoid to involve merge and io scheduler when bypass_insert
>>>> is true, otherwise, inserting is ignored, BLK_STS_RESOURCE is returned
>>>> and the caller will fail forever.
>>>>
>>>> The 2nd patch refactors the code of issue request directly to unify the
>>>> helper interface which could handle all the cases.
>>>>
>>>> The 3rd patch make blk_mq_sched_insert_requests issue requests directly
>>>> with 'bypass' false, then it needn't to handle the non-issued requests
>>>> any more.
>>>>
>>>> The 4th patch replace and kill the blk_mq_request_issue_directly.
>>>
>>> Sorry to keep iterating on this, but let's default to inserting to
>>> the dispatch list if we ever see busy from a direct dispatch. I'm fine
>>> with doing that for 4.21, as suggested by Ming, I just didn't want to
>>> fiddle with it for 4.20. This will prevent any merging on the request
>>> going forward, which I think is a much safer default.
>>>
>>> You do this already for some cases. Let's do it unconditionally for
>>> a request that was ever subjected to ->queue_rq() and we didn't either
>>> error or finish after the fact.
>>>
>> I have done it in this version if I get your point correctly.
>> Please refer to the following fragment in the 2nd patch.
>>
>> +	/*
>> +	 * If the request is issued unsuccessfully with
>> +	 * BLK_STS_DEV_RESOURCE or BLK_STS_RESOURCE, insert
>> +	 * the request to hctx dispatch list due to attached
>> +	 * lldd resource.
>> +	 */
>> +	force = true;
>> +	ret = __blk_mq_issue_directly(hctx, rq, cookie, last);
>> +out_unlock:
>> +	hctx_unlock(hctx, srcu_idx);
>> +out:
>> +	switch (ret) {
>> +	case BLK_STS_OK:
>> +		break;
>> +	case BLK_STS_DEV_RESOURCE:
>> +	case BLK_STS_RESOURCE:
>> +		if (force) {
>> +			blk_mq_request_bypass_insert(rq, run_queue);
>> +			ret = bypass ? BLK_STS_OK : ret;
>> +		} else if (!bypass) {
>> +			blk_mq_sched_insert_request(rq, false,
>> +						    run_queue, false);
>> +		}
>> +		break;
>> +	default:
> 
> You are right, I missed that you set force = true before doing the
> issue. So this looks good to me!

I applied your series. With this, we should be good to remove the
REQ_NOMERGE logic that was added for the corruption case, and the
blk_rq_can_direct_dispatch() as well?

-- 
Jens Axboe

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