Messages in this thread | | | Subject | Re: [PATCH v4 1/4] block: Add iocontext priority to request | From | Jens Axboe <> | Date | Thu, 13 Oct 2016 15:07:56 -0600 |
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On 10/13/2016 02:59 PM, Dan Williams wrote: > On Thu, Oct 13, 2016 at 1:24 PM, Jens Axboe <axboe@kernel.dk> wrote: >> On 10/13/2016 02:19 PM, Dan Williams wrote: >>> >>> On Thu, Oct 13, 2016 at 1:09 PM, Jens Axboe <axboe@kernel.dk> 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. >>> >>> >>> Assuming you always trust the kernel to know the right priority... >> >> >> If it set it in the bio, it better know what it's doing. Besides, >> there's nothing stopping the caller from checking the task priority when >> it sets it. If we do ioprio_best(), then we are effectively preventing >> anyone from submitting a bio with a lower priority than the task has >> generally set. > > Ah, that makes sense. Move the ioprio_best() decision out to whatever > code is setting bio_prio() to allow for cases where the kernel knows > best.
Yes, precisely.
-- Jens Axboe
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