Re: [PATCH v4 1/4] block: Add iocontext priority to request

From: Hannes Reinecke
Date: Sat Oct 15 2016 - 04:44:34 EST

On 10/14/2016 08:35 PM, Adam Manzananares wrote:
The 10/14/2016 07:54, Hannes Reinecke wrote:
On 10/13/2016 09:53 PM, Adam Manzanares wrote:
Patch adds an association between iocontext ioprio and the ioprio of a
request. This value 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@xxxxxxx>
block/blk-core.c | 4 +++-
include/linux/blkdev.h | 14 ++++++++++++++
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 14d7c07..361b1b9 100644
--- 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 c47c358..9a0ceaa 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -934,6 +934,20 @@ static inline unsigned int blk_rq_count_bios(struct request *rq)

+ * 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.
extern struct request *blk_peek_request(struct request_queue *q);

Don't you need to check for 'ioprio_valid()' here, too?

I poked around and it should be safe to not check for ioprio valid
at this point. ioprio_valid only checks to see if the ioprio is
not IOPRIO_CLASS_NONE. The request by default has a ioprio of none
so if the ioc has ioprio of none we are not changing anything.

The locations in the code that I found where the ioc prio is set are
either filtered through the syscall handler, which checks for invalid
priority combinations, or have valid priority values.

Thanks for the confirmation, that'll clarifies things.

Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>


Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 NÃrnberg
GF: J. Hawn, J. Guild, F. ImendÃrffer, HRB 16746 (AG NÃrnberg)