Re: [PATCH 3/3] block: introducing a bias over deadline's fifo_time

[Zhaoyang Huang]

On Fri, Feb 9, 2024 at 9:58 AM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
>
> On 2/9/24 09:28, Zhaoyang Huang wrote:
> > On Fri, Feb 9, 2024 at 8:11 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >>
> >> On 2/8/24 5:02 PM, Zhaoyang Huang wrote:
> >>> On Fri, Feb 9, 2024 at 1:49?AM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >>>>
> >>>> On 2/8/24 2:31 AM, zhaoyang.huang wrote:
> >>>>> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> >>>>> index f958e79277b8..43c08c3d6f18 100644
> >>>>> --- a/block/mq-deadline.c
> >>>>> +++ b/block/mq-deadline.c
> >>>>> @@ -15,6 +15,7 @@
> >>>>>  #include <linux/compiler.h>
> >>>>>  #include <linux/rbtree.h>
> >>>>>  #include <linux/sbitmap.h>
> >>>>> +#include "../kernel/sched/sched.h"
> >>>>>
> >>>>>  #include <trace/events/block.h>
> >>>>>
> >>>>> @@ -802,6 +803,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> >>>>>       u8 ioprio_class = IOPRIO_PRIO_CLASS(ioprio);
> >>>>>       struct dd_per_prio *per_prio;
> >>>>>       enum dd_prio prio;
> >>>>> +     int fifo_expire;
> >>>>>
> >>>>>       lockdep_assert_held(&dd->lock);
> >>>>>
> >>>>> @@ -840,7 +842,9 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> >>>>>               /*
> >>>>>                * set expire time and add to fifo list
> >>>>>                */
> >>>>> -             rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
> >>>>> +             fifo_expire = task_is_realtime(current) ? dd->fifo_expire[data_dir] :
> >>>>> +                     CFS_PROPORTION(current, dd->fifo_expire[data_dir]);
> >>>>> +             rq->fifo_time = jiffies + fifo_expire;
> >>>>>               insert_before = &per_prio->fifo_list[data_dir];
> >>>>>  #ifdef CONFIG_BLK_DEV_ZONED
> >>>>>               /*
> >>>>
> >>>> Hard pass on this blatant layering violation. Just like the priority
> >>>> changes, this utterly fails to understand how things are properly
> >>>> designed.
> >>> IMHO, I don't think this is a layering violation. bio_set_ioprio is
> >>> the one which introduces the scheduler thing into the block layer,
> >>> this commit just wants to do a little improvement based on that. This
> >>> commit helps CFS task save some IO time when preempted by RT heavily.
> >>
> >> Listen, both this and the previous content ioprio thing show a glaring
> >> misunderstanding of how to design these kinds of things. You have no
> >> grasp of what the different layers do, or how they interact. I'm not
> >> sure how to put this kindly, but it's really an awful idea to hardcore
> >> some CFS helper into the IO scheduler. The fact that you had to fiddle
> >> around with headers to make it work was the first warning sign, and the
> >> fact that you didn't stop at that point to consider how it could be
> >> properly done makes it even worse.
> >>
> >> You need to stop sending kernel patches until you understand basic
> >> software design. Neither of these patches are going anywhere until this
> >> happens. There's been plenty of feedback to telling you that, but you
> >> seem to just ignore it and plow on ahead. Stop.
> > Ok, thanks for pointing this out, I will follow your advice. But I
> > have to say that '[PATCHv9 1/1] block: introduce content activity
> > based ioprio' really solved layering violation things. I would like to
> > humbly ask for your kindly patient to have a look, as it is really
> > helpful.
>
> If properly designed, that patch would *not* be a block layer API/function and
> so does not need review by block layer folks/Jens as it would simply set an IO
> prio for a BIO issued by an FS. So that patch needs to be accepted by FS
> people, for the FS you are interested in.
Thanks for the heads-up, sorry for my none-sense on the needs of
maintaining the whole framework. IMHO, the newly introduced API is a
little bit like bio_set_pages_dirty which is mainly related to bio and
the pages inside. Patchv9 has changed a lot to meet your kind advice.
I would be grateful to you if you could review it.
>
>
> --
> Damien Le Moal
> Western Digital Research
>