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>

2 files changed, 2 insertions, 10 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 580eee5743e5..40725b9091f1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -303,15 +303,7 @@ void __blk_run_queue(struct request_queue *q)
         if (unlikely(blk_queue_stopped(q)))
                 return;
 
-        /*
-         * Only recurse once to avoid overrunning the stack, let the unplug
-         * handling reinvoke the handler shortly if we already got there.
-         */
-        if (!queue_flag_test_and_set(QUEUE_FLAG_REENTER, q)) {
-                q->request_fn(q);
-                queue_flag_clear(QUEUE_FLAG_REENTER, q);
-        } else
-                queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
+        q->request_fn(q);
 }
 EXPORT_SYMBOL(__blk_run_queue);
 
@@ -328,6 +320,7 @@ void blk_run_queue_async(struct request_queue *q)
         if (likely(!blk_queue_stopped(q)))
                 queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
 }
+EXPORT_SYMBOL(blk_run_queue_async);
 
 /**
  * blk_run_queue - run a single device queue
diff --git a/block/blk.h b/block/blk.h
index c9df8fc3c999..61263463e38e 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -22,7 +22,6 @@ void blk_rq_timed_out_timer(unsigned long data);
 void blk_delete_timer(struct request *);
 void blk_add_timer(struct request *);
 void __generic_unplug_device(struct request_queue *);
-void blk_run_queue_async(struct request_queue *q);
 
 /*
  * Internal atomic flags for request handling