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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe