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

[Adam Manzananares <adam.manzanares@wdc.com>]

The 10/13/2016 14:09, Jens Axboe wrote:
> On 10/13/2016 02:06 PM, Dan Williams wrote:
> >On Thu, Oct 13, 2016 at 12:53 PM, Adam Manzanares
> ><adam.manzanares@hgst.com> 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@wdc.com>
> >>---
> >> 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);
> >
> >Should we use ioprio_best() here?  If req->ioprio and bio_prio()
> >disagree one side has explicitly asked for a higher priority.
> 
> It's a good question - but if priority has been set in the bio, it makes
> sense that that would take priority over the general setting for the
> task/io context. So I think the patch is correct as-is.
> 
> Adam, you'll want to rewrite the commit message though. A good commit
> message should explain WHY the change is made, not detail the code
> implementation of it.

Got it I'll send something out soon.

> 
> -- 
> Jens Axboe
> 

Take care,
Adam