[PATCH V13 0/3] blk-mq: refactor code of issue directly

[PATCH V13 0/3] blk-mq: refactor code of issue directly

[Jianchao Wang]

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.

The 1st patch refactors the code of issue request directly to unify the
helper interface which could handle all the cases.

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.

V13:
 - remove the unused tag 'out' (1/3)

V12:
 - remove the original 1st patch/
 - rebase other 3 patches on newest for-4.21/block
 - add some comment

V11:
 - insert request to dispatch list when .queue_rq return
   BLK_STS_RESOURCE/BLK_STS_DEV_RESOURCE. (2/4)
 - stop to attempt direct-issue and insert the reset when meet
   non-ok case (3/4).

V10:
 - 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)

V9:
 - rebase on recent for-4.21/block
 - add 1st patch

V8:
 - drop the original 2nd patch which try to insert requests into hctx->dispatch
   if quiesced or stopped.
 - remove two wrong 'unlikely'

V7:
 - drop the original 3rd patch which try to ensure hctx to be ran on
   its mapped cpu in issueing directly path.

V6:
 - 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

V5:
 - 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

V4:
 - split the original patch 1 into two patches, 1st and 2nd patch currently
 - rename the mq_decision to mq_issue_decision
 - comment changes

V3:
 - 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.

V2:
 - 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       | 123 +++++++++++++++++++++++++--------------------------
block/blk-mq.h       |   6 ++-
4 files changed, 70 insertions(+), 71 deletions(-)

Thanks
Jianchao

[PATCH V13 1/3] blk-mq: refactor the code of issue request directly

[Jianchao Wang]

Merge blk_mq_try_issue_directly and __blk_mq_try_issue_directly
into one interface to unify the interfaces to issue requests
directly. The merged interface takes over the requests totally,
it could insert, end or do nothing based on the return value of
.queue_rq and 'bypass' parameter. Then caller needn't any other
handling any more and then code could be cleaned up.

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
---
 block/blk-mq.c | 103 ++++++++++++++++++++++++++++++---------------------------
 1 file changed, 54 insertions(+), 49 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b645275..8dc34d2 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1794,78 +1794,83 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	return ret;
 }
 
-static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 						struct request *rq,
 						blk_qc_t *cookie,
-						bool bypass_insert, bool last)
+						bool bypass, bool last)
 {
 	struct request_queue *q = rq->q;
 	bool run_queue = true;
+	blk_status_t ret = BLK_STS_RESOURCE;
+	int srcu_idx;
+	bool force = false;
 
+	hctx_lock(hctx, &srcu_idx);
 	/*
-	 * RCU or SRCU read lock is needed before checking quiesced flag.
+	 * hctx_lock is needed before checking quiesced flag.
 	 *
-	 * When queue is stopped or quiesced, ignore 'bypass_insert' from
-	 * blk_mq_request_issue_directly(), and return BLK_STS_OK to caller,
-	 * and avoid driver to try to dispatch again.
+	 * When queue is stopped or quiesced, ignore 'bypass', insert
+	 * and return BLK_STS_OK to caller, and avoid driver to try to
+	 * dispatch again.
 	 */
-	if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
+	if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) {
 		run_queue = false;
-		bypass_insert = false;
-		goto insert;
+		bypass = false;
+		goto out_unlock;
 	}
 
-	if (q->elevator && !bypass_insert)
-		goto insert;
+	if (unlikely(q->elevator && !bypass))
+		goto out_unlock;
 
 	if (!blk_mq_get_dispatch_budget(hctx))
-		goto insert;
+		goto out_unlock;
 
 	if (!blk_mq_get_driver_tag(rq)) {
 		blk_mq_put_dispatch_budget(hctx);
-		goto insert;
+		goto out_unlock;
 	}
 
-	return __blk_mq_issue_directly(hctx, rq, cookie, last);
-insert:
-	if (bypass_insert)
-		return BLK_STS_RESOURCE;
-
-	blk_mq_request_bypass_insert(rq, run_queue);
-	return BLK_STS_OK;
-}
-
-static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
-		struct request *rq, blk_qc_t *cookie)
-{
-	blk_status_t ret;
-	int srcu_idx;
-
-	might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
-
-	hctx_lock(hctx, &srcu_idx);
-
-	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
-	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
-		blk_mq_request_bypass_insert(rq, true);
-	else if (ret != BLK_STS_OK)
-		blk_mq_end_request(rq, ret);
-
+	/*
+	 * Always add a request that has been through
+	 *.queue_rq() to the hardware dispatch list.
+	 */
+	force = true;
+	ret = __blk_mq_issue_directly(hctx, rq, cookie, last);
+out_unlock:
 	hctx_unlock(hctx, srcu_idx);
+	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);
+			/*
+			 * We have to return BLK_STS_OK for the DM
+			 * to avoid livelock. Otherwise, we return
+			 * the real result to indicate whether the
+			 * request is direct-issued successfully.
+			 */
+			ret = bypass ? BLK_STS_OK : ret;
+		} else if (!bypass) {
+			blk_mq_sched_insert_request(rq, false,
+						    run_queue, false);
+		}
+		break;
+	default:
+		if (!bypass)
+			blk_mq_end_request(rq, ret);
+		break;
+	}
+
+	return ret;
 }
 
 blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 {
-	blk_status_t ret;
-	int srcu_idx;
-	blk_qc_t unused_cookie;
-	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
+	blk_qc_t unused;
 
-	hctx_lock(hctx, &srcu_idx);
-	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true, last);
-	hctx_unlock(hctx, srcu_idx);
-
-	return ret;
+	return blk_mq_try_issue_directly(rq->mq_hctx, rq, &unused, true, last);
 }
 
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
@@ -2006,13 +2011,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		if (same_queue_rq) {
 			data.hctx = same_queue_rq->mq_hctx;
 			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
-					&cookie);
+					&cookie, false, true);
 		}
 	} else if ((q->nr_hw_queues > 1 && is_sync) || (!q->elevator &&
 			!data.hctx->dispatch_busy)) {
 		blk_mq_put_ctx(data.ctx);
 		blk_mq_bio_to_request(rq, bio);
-		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
+		blk_mq_try_issue_directly(data.hctx, rq, &cookie, false, true);
 	} else {
 		blk_mq_put_ctx(data.ctx);
 		blk_mq_bio_to_request(rq, bio);
-- 
2.7.4

[PATCH V13 2/3] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert_requests

[Jianchao Wang]

It is not necessary to issue request directly with bypass 'true'
in blk_mq_sched_insert_requests and handle the non-issued requests
itself. Just set bypass to 'false' and let blk_mq_try_issue_directly
handle them totally. Remove the blk_rq_can_direct_dispatch check,
because blk_mq_try_issue_directly can handle it well.If request is
direct-issued unsuccessfully, insert the reset.

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
---
 block/blk-mq-sched.c |  8 +++-----
 block/blk-mq.c       | 20 +++++++++-----------
 2 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index f096d898..5b4d52d 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -417,12 +417,10 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
 		 * busy in case of 'none' scheduler, and this way may save
 		 * us one extra enqueue & dequeue to sw queue.
 		 */
-		if (!hctx->dispatch_busy && !e && !run_queue_async) {
+		if (!hctx->dispatch_busy && !e && !run_queue_async)
 			blk_mq_try_issue_list_directly(hctx, list);
-			if (list_empty(list))
-				return;
-		}
-		blk_mq_insert_requests(hctx, ctx, list);
+		else
+			blk_mq_insert_requests(hctx, ctx, list);
 	}
 
 	blk_mq_run_hw_queue(hctx, run_queue_async);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8dc34d2..8f554d1 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1876,22 +1876,20 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		struct list_head *list)
 {
+	blk_qc_t unused;
+	blk_status_t ret = BLK_STS_OK;
+
 	while (!list_empty(list)) {
-		blk_status_t ret;
 		struct request *rq = list_first_entry(list, struct request,
 				queuelist);
 
 		list_del_init(&rq->queuelist);
-		ret = blk_mq_request_issue_directly(rq, list_empty(list));
-		if (ret != BLK_STS_OK) {
-			if (ret == BLK_STS_RESOURCE ||
-					ret == BLK_STS_DEV_RESOURCE) {
-				blk_mq_request_bypass_insert(rq,
+		if (ret == BLK_STS_OK)
+			ret = blk_mq_try_issue_directly(hctx, rq, &unused,
+							false,
 							list_empty(list));
-				break;
-			}
-			blk_mq_end_request(rq, ret);
-		}
+		else
+			blk_mq_sched_insert_request(rq, false, true, false);
 	}
 
 	/*
@@ -1899,7 +1897,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 	 * the driver there was more coming, but that turned out to
 	 * be a lie.
 	 */
-	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs)
+	if (ret != BLK_STS_OK && hctx->queue->mq_ops->commit_rqs)
 		hctx->queue->mq_ops->commit_rqs(hctx);
 }
 
-- 
2.7.4

[PATCH V13 3/3] blk-mq: replace and kill blk_mq_request_issue_directly

[Jianchao Wang]

Replace blk_mq_request_issue_directly with blk_mq_try_issue_directly
in blk_insert_cloned_request and kill it as nobody uses it any more.

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
---
 block/blk-core.c | 4 +++-
 block/blk-mq.c   | 9 +--------
 block/blk-mq.h   | 6 ++++--
 3 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index ad59102..c92d866 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1297,6 +1297,8 @@ static int blk_cloned_rq_check_limits(struct request_queue *q,
  */
 blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *rq)
 {
+	blk_qc_t unused;
+
 	if (blk_cloned_rq_check_limits(q, rq))
 		return BLK_STS_IOERR;
 
@@ -1312,7 +1314,7 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *
 	 * bypass a potential scheduler on the bottom device for
 	 * insert.
 	 */
-	return blk_mq_request_issue_directly(rq, true);
+	return blk_mq_try_issue_directly(rq->mq_hctx, rq, &unused, true, true);
 }
 EXPORT_SYMBOL_GPL(blk_insert_cloned_request);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8f554d1..890d074 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1794,7 +1794,7 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	return ret;
 }
 
-static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 						struct request *rq,
 						blk_qc_t *cookie,
 						bool bypass, bool last)
@@ -1866,13 +1866,6 @@ static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 	return ret;
 }
 
-blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
-{
-	blk_qc_t unused;
-
-	return blk_mq_try_issue_directly(rq->mq_hctx, rq, &unused, true, last);
-}
-
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		struct list_head *list)
 {
diff --git a/block/blk-mq.h b/block/blk-mq.h
index a664ea4..b81e619 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -68,8 +68,10 @@ void blk_mq_request_bypass_insert(struct request *rq, bool run_queue);
 void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 				struct list_head *list);
 
-/* Used by blk_insert_cloned_request() to issue request directly */
-blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last);
+blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+						struct request *rq,
+						blk_qc_t *cookie,
+						bool bypass, bool last);
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 				    struct list_head *list);
 
-- 
2.7.4

Re: [PATCH V13 0/3] blk-mq: refactor code of issue directly

[jianchao.wang]

Ping ?

Thanks
Jianchao

On 12/10/18 11:01 AM, 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.
> 
> The 1st patch refactors the code of issue request directly to unify the
> helper interface which could handle all the cases.
> 
> 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.
> 
> V13:
>  - remove the unused tag 'out' (1/3)
> 
> V12:
>  - remove the original 1st patch/
>  - rebase other 3 patches on newest for-4.21/block
>  - add some comment
> 
> V11:
>  - insert request to dispatch list when .queue_rq return
>    BLK_STS_RESOURCE/BLK_STS_DEV_RESOURCE. (2/4)
>  - stop to attempt direct-issue and insert the reset when meet
>    non-ok case (3/4).
> 
> V10:
>  - 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)
> 
> V9:
>  - rebase on recent for-4.21/block
>  - add 1st patch
> 
> V8:
>  - drop the original 2nd patch which try to insert requests into hctx->dispatch
>    if quiesced or stopped.
>  - remove two wrong 'unlikely'
> 
> V7:
>  - drop the original 3rd patch which try to ensure hctx to be ran on
>    its mapped cpu in issueing directly path.
> 
> V6:
>  - 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
> 
> V5:
>  - 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
> 
> V4:
>  - split the original patch 1 into two patches, 1st and 2nd patch currently
>  - rename the mq_decision to mq_issue_decision
>  - comment changes
> 
> V3:
>  - 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.
> 
> V2:
>  - 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       | 123 +++++++++++++++++++++++++--------------------------
> block/blk-mq.h       |   6 ++-
> 4 files changed, 70 insertions(+), 71 deletions(-)
> 
> Thanks
> Jianchao
> 
>