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Date: Fri, 23 Dec 2022 06:53:08 +0100
From: Christoph Hellwig <hch@....de>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: axboe@...nel.dk, dwagner@...e.de, hare@...e.de,
ming.lei@...hat.com, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, hch@....de, john.garry@...wei.com
Subject: Re: [PATCH 12/13] blk-mq: use switch/case to improve readability
in blk_mq_try_issue_list_directly
On Fri, Dec 23, 2022 at 08:52:22PM +0800, Kemeng Shi wrote:
> + blk_mq_request_bypass_insert(rq, false, list_empty(list));
Please try to avoid the overly long line here.
That beng said blk_mq_request_bypass_insert is simply a horrible
API. I think we should do something like this:
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 53202eff545efb..b6157ae11df651 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -432,7 +432,8 @@ void blk_insert_flush(struct request *rq)
*/
if ((policy & REQ_FSEQ_DATA) &&
!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
- blk_mq_request_bypass_insert(rq, false, true);
+ blk_mq_request_bypass_insert(rq);
+ blk_mq_run_hw_queue(rq->mq_hctx, false);
return;
}
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 23d1a90fec4271..d49fe4503b09d7 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -437,12 +437,13 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
* Simply queue flush rq to the front of hctx->dispatch so that
* intensive flush workloads can benefit in case of NCQ HW.
*/
- at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
- blk_mq_request_bypass_insert(rq, at_head, false);
- goto run;
- }
-
- if (e) {
+ spin_lock(&hctx->lock);
+ if ((rq->rq_flags & RQF_FLUSH_SEQ) || at_head)
+ list_add(&rq->queuelist, &hctx->dispatch);
+ else
+ list_add_tail(&rq->queuelist, &hctx->dispatch);
+ spin_unlock(&hctx->lock);
+ } else if (e) {
LIST_HEAD(list);
list_add(&rq->queuelist, &list);
@@ -453,7 +454,6 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
spin_unlock(&ctx->lock);
}
-run:
if (run_queue)
blk_mq_run_hw_queue(hctx, async);
}
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c5cf0dbca1db8d..43bb9b36c90da7 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1467,7 +1467,7 @@ static void blk_mq_requeue_work(struct work_struct *work)
* merge.
*/
if (rq->rq_flags & RQF_DONTPREP)
- blk_mq_request_bypass_insert(rq, false, false);
+ blk_mq_request_bypass_insert(rq);
else
blk_mq_sched_insert_request(rq, true, false, false);
}
@@ -2504,26 +2504,17 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
/**
* blk_mq_request_bypass_insert - Insert a request at dispatch list.
* @rq: Pointer to request to be inserted.
- * @at_head: true if the request should be inserted at the head of the list.
- * @run_queue: If we should run the hardware queue after inserting the request.
*
* Should only be used carefully, when the caller knows we want to
* bypass a potential IO scheduler on the target device.
*/
-void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
- bool run_queue)
+void blk_mq_request_bypass_insert(struct request *rq)
{
struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
spin_lock(&hctx->lock);
- if (at_head)
- list_add(&rq->queuelist, &hctx->dispatch);
- else
- list_add_tail(&rq->queuelist, &hctx->dispatch);
+ list_add_tail(&rq->queuelist, &hctx->dispatch);
spin_unlock(&hctx->lock);
-
- if (run_queue)
- blk_mq_run_hw_queue(hctx, false);
}
void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
@@ -2670,10 +2661,17 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
blk_status_t ret =
__blk_mq_try_issue_directly(hctx, rq, false, true);
- if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
- blk_mq_request_bypass_insert(rq, false, true);
- else if (ret != BLK_STS_OK)
+ switch (ret) {
+ case BLK_STS_OK:
+ break;
+ case BLK_STS_RESOURCE:
+ case BLK_STS_DEV_RESOURCE:
+ blk_mq_request_bypass_insert(rq);
+ blk_mq_run_hw_queue(rq->mq_hctx, false);
+ break;
+ default:
blk_mq_end_request(rq, ret);
+ }
}
static blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
@@ -2705,7 +2703,8 @@ static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
break;
case BLK_STS_RESOURCE:
case BLK_STS_DEV_RESOURCE:
- blk_mq_request_bypass_insert(rq, false, true);
+ blk_mq_request_bypass_insert(rq);
+ blk_mq_run_hw_queue(rq->mq_hctx, false);
blk_mq_commit_rqs(hctx, &queued, from_schedule);
return;
default:
@@ -2818,8 +2817,9 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
errors++;
if (ret == BLK_STS_RESOURCE ||
ret == BLK_STS_DEV_RESOURCE) {
- blk_mq_request_bypass_insert(rq, false,
- list_empty(list));
+ blk_mq_request_bypass_insert(rq);
+ if (list_empty(list))
+ blk_mq_run_hw_queue(rq->mq_hctx, false);
break;
}
blk_mq_end_request(rq, ret);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index ef59fee62780d3..3733429561e1eb 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -61,8 +61,7 @@ void blk_mq_free_map_and_rqs(struct blk_mq_tag_set *set,
*/
void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
bool at_head);
-void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
- bool run_queue);
+void blk_mq_request_bypass_insert(struct request *rq);
void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
struct list_head *list);
void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
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