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.
> > + if (ioprio_class == IOPRIO_CLASS_NONE)
> > + bio->bi_ioprio = get_current_ioprio();
> > }
> > /**
>
> Beside this comment, I am still scratching my head regarding what the user
> gets with ioprio_get(). If I understood your patches correctly, the user may
> still see IOPRIO_CLASS_NONE ?
> For that case, to be in sync with the man page, I thought the returned
> ioprio should be the effective one based on the task io nice value, that is,
> the value returned by get_current_ioprio(). Am I missing something... ?
The trouble with returning "effective ioprio" is that with IOPRIO_WHO_PGRP
or IOPRIO_WHO_USER the effective IO priority may be different for different
processes considered and it can be also further influenced by blk-ioprio
settings. But thinking about it now after things have settled I agree that
what you suggests makes more sense. I'll fix that. Thanks for suggestion!
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
