blk-mq: unify hctx delay_work and run_work

The only difference between ->run_work and ->delay_work, is that
the latter is used to defer running a queue. This is done by
marking the queue stopped, and scheduling ->delay_work to run
sometime in the future. While the queue is stopped, direct runs
or runs through ->run_work will not run the queue.

If we combine the handlers, then we need to handle two things:

1) If a delayed/stopped run is scheduled, then we should not run
   the queue before that has been completed.
2) If a queue is delayed/stopped, the handler needs to restart
   the queue. Normally a run of a queue with the stopped bit set
   would be a no-op.

Case 1 is handled by modifying a currently pending queue run
to the deadline set by the caller of blk_mq_delay_queue().
Subsequent attempts to queue a queue run will find the work
item already pending, and direct runs will see a stopped queue
as before.

Case 2 is handled by adding a new bit, BLK_MQ_S_START_ON_RUN,
that tells the work handler that it should clear a stopped
queue and run the handler.

Reviewed-by: Bart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index c7cc90328426..f3e5e1de1bdb 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -51,8 +51,6 @@ struct blk_mq_hw_ctx {
 
 	atomic_t		nr_active;
 
-	struct delayed_work	delay_work;
-
 	struct hlist_node	cpuhp_dead;
 	struct kobject		kobj;
 
@@ -168,6 +166,7 @@ enum {
 	BLK_MQ_S_TAG_ACTIVE	= 1,
 	BLK_MQ_S_SCHED_RESTART	= 2,
 	BLK_MQ_S_TAG_WAITING	= 3,
+	BLK_MQ_S_START_ON_RUN	= 4,
 
 	BLK_MQ_MAX_DEPTH	= 10240,