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blk-mq-sched: change ->dispatch_requests() to ->dispatch_request()

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When we invoke dispatch_requests(), the scheduler empties everything
into the passed in list. This isn't always a good thing, since it
means that we remove items that we could have potentially merged
with.

Change the function to dispatch single requests at the time. If
we do that, we can backoff exactly at the point where the device
can't consume more IO, and leave the rest with the scheduler for
better merging and future dispatch decision making.

Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Tested-by: Hannes Reinecke <hare@suse.com>
This commit is contained in:
Jens Axboe 2017-01-26 12:40:07 -07:00
parent 50e1dab86a
commit c13660a08c
4 changed files with 22 additions and 13 deletions
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2
include/linux/elevator.h
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@ -92,7 +92,7 @@ struct elevator_mq_ops {
struct request *(*get_request)(struct request_queue *, unsigned int, struct blk_mq_alloc_data *);
void (*put_request)(struct request *);
void (*insert_requests)(struct blk_mq_hw_ctx *, struct list_head *, bool);
void (*dispatch_requests)(struct blk_mq_hw_ctx *, struct list_head *);
struct request *(*dispatch_request)(struct blk_mq_hw_ctx *);
bool (*has_work)(struct blk_mq_hw_ctx *);
void (*completed_request)(struct blk_mq_hw_ctx *, struct request *);
void (*started_request)(struct request *);