[PATCH V14 0/3] blk-mq: refactor and fix the code of issue directly

From: Jianchao Wang
Date: Thu Dec 13 2018 - 20:29:28 EST

Hi Jens

After commit c616cbee ( blk-mq: punt failed direct issue to dispatch
list ), we always insert request to hctx dispatch list whenever get a
BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE, this is overkill and will
harm the merging. We just need to do that for the requests that has
been through .queue_rq.

This patch set fixes the issue above and refactors the code of issue
request directly to unify the interface and make the code clearer and
more readable.

Please consider this patchset for 4.21.

The 1st patch refactors the code of issue request directly to unify the
helper interface which could handle all the cases. And also it does more
reasonable decision about how to insert the requests.

The 2nd 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 3rd patch replace and kill the blk_mq_request_issue_directly.

- change some comment

- remove the unused tag 'out' (1/3)

- remove the original 1st patch/
- rebase other 3 patches on newest for-4.21/block
- add some comment

- insert request to dispatch list when .queue_rq return
- stop to attempt direct-issue and insert the reset when meet
non-ok case (3/4).

- address Jen's comment.
- let blk_mq_try_issue_directly return actual result for case
'bypass == false'. (2/4)
- use return value of blk_mq_try_issue_directly to identify
whether the request is direct-issued successfully. (3/4)

- rebase on recent for-4.21/block
- add 1st patch

- drop the original 2nd patch which try to insert requests into hctx->dispatch
if quiesced or stopped.
- remove two wrong 'unlikely'

- drop the original 3rd patch which try to ensure hctx to be ran on
its mapped cpu in issueing directly path.

- drop original 1st patch to address Jen's comment
- discard the enum mq_issue_decision and blk_mq_make_decision and use
BLK_STS_* return values directly to address Jen's comment. (1/5)
- add 'unlikely' in blk_mq_try_issue_directly (1/5)
- refactor the 2nd and 3rd patch based on the new 1st patch.
- reserve the unused_cookie in 4th and 5th patch

- rebase against Jens' for-4.21/block branch
- adjust the order of patch04 and patch05
- add patch06 to replace and kill the one line blk_mq_request_bypass_insert
- comment changes

- split the original patch 1 into two patches, 1st and 2nd patch currently
- rename the mq_decision to mq_issue_decision
- comment changes

- Correct the code about the case bypass_insert is true and io scheduler
attached. The request still need to be issued in case above. (1/4)
- Refactor the code to make code clearer. blk_mq_make_request is introduced
to decide insert, end or just return based on the return value of .queue_rq
and bypass_insert (1/4)
- Add the 2nd patch. It introduce a new decision result which indicates to
insert request with blk_mq_request_bypass_insert.
- Modify the code to adapt the new patch 1.

- Add 1st and 2nd patch to refactor the code.

Jianchao Wang (3)
blk-mq: refactor the code of issue request directly
blk-mq: issue directly with bypass 'false' in
blk-mq: replace and kill blk_mq_request_issue_directly

block/blk-core.c | 4 +++-
block/blk-mq-sched.c | 8 +++----
block/blk-mq.c | 122 ++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------------------------
block/blk-mq.h | 6 +++--
4 files changed, 69 insertions(+), 71 deletions(-)