From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: ming.lei@redhat.com, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V11 0/4] blk-mq: refactor code of issue directly
Date: Fri, 7 Dec 2018 11:46:43 +0800 [thread overview]
Message-ID: <38eb7c50-dfad-d9cb-f8ab-a8f5250b0ed7@oracle.com> (raw)
In-Reply-To: <1e183b77-2c4d-71ff-b019-2b1070d2ed6b@kernel.dk>
On 12/7/18 11:42 AM, Jens Axboe wrote:
> On 12/6/18 8:41 PM, jianchao.wang wrote:
>>
>>
>> On 12/7/18 11:34 AM, Jens Axboe wrote:
>>> 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?
>>>
>>
>> Yes, it should be that.
>> Every thing rejected by .queue_rq is ended or inserted into hctx dispatch
>> list. And also direct-issue path is unified with normal path.
>
> Why are we doing that return value dance, depending on whether this
> is a bypass insert or not? That seems confusing.
>
For the 'bypass == false' case, it need to know whether the request is issued
successfully. This is for the 3rd patch.
I used to use the returned cookie to identify the result, but you don't like it.
So I have to use this return value.
Thanks
Jianchao
next prev parent reply other threads:[~2018-12-07 3:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-07 3:09 [PATCH V11 0/4] blk-mq: refactor code of issue directly Jianchao Wang
2018-12-07 3:09 ` [PATCH V11 1/4] blk-mq: insert to hctx dispatch list when bypass_insert is true Jianchao Wang
2018-12-07 3:09 ` [PATCH V11 2/4] blk-mq: refactor the code of issue request directly Jianchao Wang
2018-12-07 3:09 ` [PATCH V11 3/4] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert_requests Jianchao Wang
2018-12-07 3:09 ` [PATCH V11 4/4] blk-mq: replace and kill blk_mq_request_issue_directly Jianchao Wang
2018-12-07 3:16 ` [PATCH V11 0/4] blk-mq: refactor code of issue directly Jens Axboe
2018-12-07 3:26 ` jianchao.wang
2018-12-07 3:32 ` Jens Axboe
2018-12-07 3:34 ` Jens Axboe
2018-12-07 3:41 ` jianchao.wang
2018-12-07 3:42 ` Jens Axboe
2018-12-07 3:46 ` jianchao.wang [this message]
2018-12-07 3:47 ` Jens Axboe
2018-12-10 1:18 ` jianchao.wang
2018-12-10 1:27 ` Jens Axboe
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