block: Add iocontext priority to request

Patch adds an association between iocontext ioprio and the ioprio of a
request. This is done to enable request based drivers the ability to
act on priority information stored in the request. An example being
ATA devices that support command priorities. If the ATA driver discovers
that the device supports command priorities and the request has valid
priority information indicating the request is high priority, then a high
priority command can be sent to the device. This should improve tail
latencies for high priority IO on any device that queues requests
internally and can make use of the priority information stored in the
request.

The ioprio of the request is set in blk_rq_set_prio which takes the
request and the ioc as arguments. If the ioc is valid in blk_rq_set_prio
then the iopriority of the request is set as the iopriority of the ioc.
In init_request_from_bio a check is made to see if the ioprio of the bio
is valid and if so then the request prio comes from the bio.

Signed-off-by: Adam Manzananares <adam.manzanares@wdc.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/block/blk-core.c b/block/blk-core.c
index 14d7c0740dc07aa82e6d85b721daa5a7045e14f7..361b1b965d890f166835285c31803b6a42b954a5 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1153,6 +1153,7 @@ static struct request *__get_request(struct request_list *rl, int op,
 
        blk_rq_init(q, rq);
        blk_rq_set_rl(rq, rl);
+       blk_rq_set_prio(rq, ioc);
        req_set_op_attrs(rq, op, op_flags | REQ_ALLOCED);
 
        /* init elvpriv */
@@ -1656,7 +1657,8 @@ void init_request_from_bio(struct request *req, struct bio *bio)
 
        req->errors = 0;
        req->__sector = bio->bi_iter.bi_sector;
-       req->ioprio = bio_prio(bio);
+       if (ioprio_valid(bio_prio(bio)))
+               req->ioprio = bio_prio(bio);
        blk_rq_bio_prep(req->q, req, bio);
 }
 

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c47c358ba0529c7184e3fe22d70ec8fee8ecb1e6..9a0ceaa1b7e6dcf0e6e8a3bedaec16a21a5ec8b8 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -933,6 +933,20 @@ static inline unsigned int blk_rq_count_bios(struct request *rq)
        return nr_bios;
 }
 
+/*
+ * blk_rq_set_prio - associate a request with prio from ioc
+ * @rq: request of interest
+ * @ioc: target iocontext
+ *
+ * Assocate request prio with ioc prio so request based drivers
+ * can leverage priority information.
+ */
+static inline void blk_rq_set_prio(struct request *rq, struct io_context *ioc)
+{
+       if (ioc)
+               rq->ioprio = ioc->ioprio;
+}
+
 /*
  * Request issue related functions.
  */