diff options
| author | Ming Lei <ming.lei@redhat.com> | 2017-10-14 17:22:29 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2017-11-01 08:20:02 -0600 |
| commit | de1482974080ec9ef414bf048b2646b246b63f6e (patch) | |
| tree | 3ecdc2b581a83848c43205c2fd9b6e97a6808f6a /include | |
| parent | 63ba8e31c3ac6393b07c6e18538814a730478766 (diff) | |
blk-mq: introduce .get_budget and .put_budget in blk_mq_ops
For SCSI devices, there is often a per-request-queue depth, which needs
to be respected before queuing one request.
Currently blk-mq always dequeues the request first, then calls
.queue_rq() to dispatch the request to lld. One obvious issue with this
approach is that I/O merging may not be successful, because when the
per-request-queue depth can't be respected, .queue_rq() has to return
BLK_STS_RESOURCE, and then this request has to stay in hctx->dispatch
list. This means it never gets a chance to be merged with other IO.
This patch introduces .get_budget and .put_budget callback in blk_mq_ops,
then we can try to get reserved budget first before dequeuing request.
If the budget for queueing I/O can't be satisfied, we don't need to
dequeue request at all. Hence the request can be left in the IO
scheduler queue, for more merging opportunities.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/blk-mq.h | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 50c6485cb04f..901457df3d64 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -90,6 +90,8 @@ struct blk_mq_queue_data { typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *, const struct blk_mq_queue_data *); +typedef blk_status_t (get_budget_fn)(struct blk_mq_hw_ctx *); +typedef void (put_budget_fn)(struct blk_mq_hw_ctx *); typedef enum blk_eh_timer_return (timeout_fn)(struct request *, bool); typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int); typedef void (exit_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int); @@ -112,6 +114,15 @@ struct blk_mq_ops { queue_rq_fn *queue_rq; /* + * Reserve budget before queue request, once .queue_rq is + * run, it is driver's responsibility to release the + * reserved budget. Also we have to handle failure case + * of .get_budget for avoiding I/O deadlock. + */ + get_budget_fn *get_budget; + put_budget_fn *put_budget; + + /* * Called on request timeout */ timeout_fn *timeout; |