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

["jianchao.wang" <jianchao.w.wang@oracle.com>]

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:


Thanks
Jianchao