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SubjectRe: [PATCH V11 0/4] blk-mq: refactor code of issue directly
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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!

--
Jens Axboe

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