block: get rid of QUEUE_FLAG_REENTER

We are currently using this flag to check whether it's safe
to call into ->request_fn(). If it is set, we punt to kblockd.
But we get a lot of false positives and excessive punts to
kblockd, which hurts performance.

The only real abuser of this infrastructure is SCSI. So export
the async queue run and convert SCSI over to use that. There's
room for improvement in that SCSI need not always use the async
call, but this fixes our performance issue and they can fix that
up in due time.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 1 insertions, 16 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ab55c2fa7ce..e9901b8f844 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -411,8 +411,6 @@ static void scsi_run_queue(struct request_queue *q)
 	list_splice_init(&shost->starved_list, &starved_list);
 
 	while (!list_empty(&starved_list)) {
-		int flagset;
-
 		/*
 		 * As long as shost is accepting commands and we have
 		 * starved queues, call blk_run_queue. scsi_request_fn
@@ -435,20 +433,7 @@ static void scsi_run_queue(struct request_queue *q)
 			continue;
 		}
 
-		spin_unlock(shost->host_lock);
-
-		spin_lock(sdev->request_queue->queue_lock);
-		flagset = test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) &&
-				!test_bit(QUEUE_FLAG_REENTER,
-					&sdev->request_queue->queue_flags);
-		if (flagset)
-			queue_flag_set(QUEUE_FLAG_REENTER, sdev->request_queue);
-		__blk_run_queue(sdev->request_queue);
-		if (flagset)
-			queue_flag_clear(QUEUE_FLAG_REENTER, sdev->request_queue);
-		spin_unlock(sdev->request_queue->queue_lock);
-
-		spin_lock(shost->host_lock);
+		blk_run_queue_async(sdev->request_queue);
 	}
 	/* put any unprocessed entries back */
 	list_splice(&starved_list, &shost->starved_list);