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

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Message-ID: <fba9f099-4fb6-6679-b9c5-4f9aa8cf291e@suse.de>
Date:   Sat, 15 Oct 2016 10:43:56 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Adam Manzananares <adam.manzanares@....com>
Cc:     Adam Manzanares <adam.manzanares@...t.com>, axboe@...nel.dk,
        tj@...nel.org, dan.j.williams@...el.com,
        martin.petersen@...cle.com, mchristi@...hat.com,
        toshi.kani@....com, ming.lei@...onical.com,
        sathya.prakash@...adcom.com, chaitra.basappa@...adcom.com,
        suganath-prabu.subramani@...adcom.com, linux-block@...r.kernel.org,
        linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
        MPT-FusionLinux.pdl@...adcom.com, linux-scsi@...r.kernel.org
Subject: Re: [PATCH v4 1/4] block: Add iocontext priority to request

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@....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);
>>>  	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@...e.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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