[PATCH 1/5] block: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE

[Ming Lei]

If .queue_rq() returns BLK_STS_RESOURCE, blk-mq will rerun
the queue in the three situations:

1) if BLK_MQ_S_SCHED_RESTART is set
- queue is rerun after one rq is completed, see blk_mq_sched_restart()
which is run from blk_mq_free_request()

2) BLK_MQ_S_TAG_WAITING is set
- queue is rerun after one tag is freed

3) otherwise
- queue is run immediately in blk_mq_dispatch_rq_list()

So calling blk_mq_delay_run_hw_queue() inside .queue_rq() doesn't make
sense because no matter it is called or not, the queue still will be
rerun soon in above three situations, and the busy req can be dispatched
again.

Cc: Mike Snitzer <snit...@redhat.com>
Cc: dm-de...@redhat.com
Cc: Sagi Grimberg <s...@grimberg.me>
Cc: linux-n...@lists.infradead.org
Cc: "James E.J. Bottomley" <j...@linux.vnet.ibm.com>
Cc: "Martin K. Petersen" <martin.peter...@oracle.com>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Ming Lei <ming....@redhat.com>
---
 drivers/md/dm-rq.c      | 1 -
 drivers/nvme/host/fc.c  | 3 ---
 drivers/scsi/scsi_lib.c | 4 ----
 3 files changed, 8 deletions(-)

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index c6ebc5b1e00e..71422cea1c4a 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -761,7 +761,6 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx 
*hctx,
                /* Undo dm_start_request() before requeuing */
                rq_end_stats(md, rq);
                rq_completed(md, rq_data_dir(rq), false);
-               blk_mq_delay_run_hw_queue(hctx, 100/*ms*/);
                return BLK_STS_RESOURCE;
        }
 
diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index d2e882c0f496..17727eee5d5f 100644
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -2041,9 +2041,6 @@ nvme_fc_start_fcp_op(struct nvme_fc_ctrl *ctrl, struct 
nvme_fc_queue *queue,
        return BLK_STS_OK;
 
 busy:
-       if (!(op->flags & FCOP_FLAGS_AEN) && queue->hctx)
-               blk_mq_delay_run_hw_queue(queue->hctx, NVMEFC_QUEUE_DELAY);
-
        return BLK_STS_RESOURCE;
 }
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9cf6a80fe297..71d5bf1345c9 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2010,11 +2010,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx 
*hctx,
 out:
        switch (ret) {
        case BLK_STS_OK:
-               break;
        case BLK_STS_RESOURCE:
-               if (atomic_read(&sdev->device_busy) == 0 &&
-                   !scsi_device_blocked(sdev))
-                       blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY);
                break;
        default:
                /*
-- 
2.9.5