Re: [PATCH 1/1] blk-throttle: fix throttle configuring not effective

[Yu Kuai]

+CC Michal.

在 2023/08/12 15:53, Yu Kuai 写道:
> Hi,
>
> 在 2023/08/12 15:21, zhuxiaohui 写道:
> > when updating block throttle limit with persistence and stable io
> > pressure, especially a relative high io pressure, fio test e.g.,
> > there may never be a change to start a new slice, and carryover_ios &
> > carryover_bytes will not be cleared.
> >
> > As a result, when reconfiguring block throttle limit, we can notice that
> > the actual iops and throughput is a random value far away from what is
> > set
> >
> > So we need to update carryover value when dispatching bio
>
> I don't understand, not clear carryover_bytes/ios is what expected, and
> how can they affect actual bandwith/iops.
>
> Can you give a example how you tested and why current calculation is not
> correct?

I can reporduce this, but this patch is obviously wrong. You must
explaim how the calculation is not correct.

After a quick loock, I found that carryover_bytes/ios is not updated in
throtl_trim_slice(), while tg->io/bytes_disp[] can be cleared. This is
definitly a problem.

Thanks,
Kuai

> Thanks,
> Kuai
>
> > Signed-off-by: zhuxiaohui <zhuxiaohui.400@xxxxxxxxxxxxx>
> > ---
> >   block/blk-throttle.c | 26 ++++++++++++++++++++++++++
> >   block/blk-throttle.h |  4 ++--
> >   2 files changed, 28 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> > index 7397ff199d66..13c9d87a7201 100644
> > --- a/block/blk-throttle.c
> > +++ b/block/blk-throttle.c
> > @@ -821,6 +821,30 @@ static void tg_update_carryover(struct throtl_grp 
> > *tg)
> >              tg->carryover_ios[READ], tg->carryover_ios[WRITE]);
> >   }
> > +static void tg_charge_carryover(struct throtl_grp *tg, struct bio *bio)
> > +{
> > +    bool rw = bio_data_dir(bio);
> > +
> > +    if (unlikely(tg->carryover_bytes[rw])) {
> > +        unsigned int bio_size = throtl_bio_data_size(bio);
> > +        unsigned int carryout_size = abs(tg->carryover_bytes[rw]);
> > +
> > +        carryout_size = min(carryout_size, bio_size);
> > +
> > +        if (tg->carryover_bytes[rw] < 0)
> > +            tg->carryover_bytes[rw] += carryout_size;
> > +        else
> > +            tg->carryover_bytes[rw] -= carryout_size;
> > +    }
> > +
> > +    if (unlikely(tg->carryover_ios[rw])) {
> > +        if (tg->carryover_ios[rw] < 0)
> > +            tg->carryover_ios[rw] += 1;
> > +        else
> > +            tg->carryover_ios[rw] -= 1;
> > +    }
> > +}
> > +
> >   static unsigned long tg_within_iops_limit(struct throtl_grp *tg, 
> > struct bio *bio,
> >                    u32 iops_limit)
> >   {
> > @@ -965,6 +989,8 @@ static void throtl_charge_bio(struct throtl_grp 
> > *tg, struct bio *bio)
> >       tg->io_disp[rw]++;
> >       tg->last_io_disp[rw]++;
> > +
> > +    tg_charge_carryover(tg, bio);
> >   }
> >   /**
> > diff --git a/block/blk-throttle.h b/block/blk-throttle.h
> > index d1ccbfe9f797..8f1642becb23 100644
> > --- a/block/blk-throttle.h
> > +++ b/block/blk-throttle.h
> > @@ -127,8 +127,8 @@ struct throtl_grp {
> >        * bytes/ios are waited already in previous configuration, and 
> > they will
> >        * be used to calculate wait time under new configuration.
> >        */
> > -    uint64_t carryover_bytes[2];
> > -    unsigned int carryover_ios[2];
> > +    int64_t carryover_bytes[2];
> > +    int carryover_ios[2];
> >       unsigned long last_check_time;
>
> .