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

[Zhaoyang Huang]

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.
>
> --
> Jens Axboe
>