On 6/17/22 20:52, Jan Kara wrote:
> On Fri 17-06-22 09:05:12, Damien Le Moal wrote:
>> On 6/16/22 20:23, Jan Kara wrote:
>>> On Thu 16-06-22 12:15:25, Damien Le Moal wrote:
>>>> On 6/16/22 01:16, Jan Kara wrote:
>>>>> Currently, IO priority set in task's IO context is not reflected in the
>>>>> bio->bi_ioprio for most IO (only io_uring and direct IO set it). This
>>>>> results in odd results where process is submitting some bios with one
>>>>> priority and other bios with a different (unset) priority and due to
>>>>> differing priorities bios cannot be merged. Make sure bio->bi_ioprio is
>>>>> always set on bio submission.
>>>>>
>>>>> Signed-off-by: Jan Kara <jack@xxxxxxx>
>>>>> ---
>>>>> block/blk-mq.c | 6 ++++++
>>>>> 1 file changed, 6 insertions(+)
>>>>>
>>>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>>>> index e17d822e6051..e976f696babc 100644
>>>>> --- a/block/blk-mq.c
>>>>> +++ b/block/blk-mq.c
>>>>> @@ -2793,7 +2793,13 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
>>>>> static void bio_set_ioprio(struct bio *bio)
>>>>> {
>>>>> + unsigned short ioprio_class;
>>>>> +
>>>>> blkcg_set_ioprio(bio);
>>>>
>>>> Shouldn't this function set the default using the below "if" code ?
>>>>
>>>>> + ioprio_class = IOPRIO_PRIO_CLASS(bio->bi_ioprio);
>>>>> + /* Nobody set ioprio so far? Initialize it based on task's nice value */
>>>>
>>>> I do not think that the ioprio_class variable is useful.
>>>> This can be:
>>>>
>>>> if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) == IOPRIO_CLASS_NONE)
>>>> bio->bi_ioprio = get_current_ioprio();
>>>
>>> You are right. Fixed.
>>
>> What about moving this inside blkcg_set_ioprio() ? bio_set_ioprio() would
>> then not be needed at all and blkcg_set_ioprio() called directly ?
>
> What I dislike about this is that it is counterintuitive that
> blkcg_set_prio() does anything when blkcgs are disabled in kernel config
> (and it would have to to keep things working). So if you dislike
> bio_set_ioprio(), I can just opencode this function in its single call
> site. Would that be better?
Ah, yes, blkcg may be disabled. Got it. So sure, bio_set_ioprio() is fine
as is.
>
> Honza
--
Damien Le Moal
Western Digital Research
