blk-mq: add blk_mq_delay_queue

Add a blk-mq equivalent to blk_delay_queue so that the scsi layer can ask
to be kicked again after a delay.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Modified by me to kill the unnecessary preempt disable/enable
in the delayed workqueue handler.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 9ecfab9..ae868e7 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -18,7 +18,8 @@
 	} ____cacheline_aligned_in_smp;
 
 	unsigned long		state;		/* BLK_MQ_S_* flags */
-	struct delayed_work	delayed_work;
+	struct delayed_work	run_work;
+	struct delayed_work	delay_work;
 	cpumask_var_t		cpumask;
 
 	unsigned long		flags;		/* BLK_MQ_F_* flags */
@@ -158,6 +159,7 @@
 void blk_mq_start_hw_queue(struct blk_mq_hw_ctx *hctx);
 void blk_mq_stop_hw_queues(struct request_queue *q);
 void blk_mq_start_stopped_hw_queues(struct request_queue *q, bool async);
+void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs);
 
 /*
  * Driver command data is immediately after the request. So subtract request