Re: [External] Re: [PATCH] blk-throttle: Fix io statistics for cgroup v1

[hanjinke]

在 2023/3/31 上午9:44, Tejun Heo 写道:
> Hello,
>
> On Thu, Mar 30, 2023 at 11:44:04AM +0800, hanjinke wrote:
> > 在 2023/3/30 上午2:54, Tejun Heo 写道:
> > > On Tue, Mar 28, 2023 at 10:23:09PM +0800, Jinke Han wrote:
> > > > From: Jinke Han <hanjinke.666@xxxxxxxxxxxxx>
> > > >
> > > > Now the io statistics of cgroup v1 are no longer accurate. Although
> > > > in the long run it's best that rstat is a good implementation of
> > > > cgroup v1 io statistics. But before that, we'd better fix this issue.
> > >
> > > Can you please expand on how the stats are wrong on v1 and how the patch
> > > fixes it?
> > >
> > > Thanks.
> > Now blkio.throttle.io_serviced and blkio.throttle.io_serviced become the
>
> "now" might be a bit too vague. Can you point to the commit which made the
> change?
>
> > only stable io stats interface of cgroup v1, and these statistics are done
> > in the blk-throttle code. But the current code only counts the bios that are
>
> Ah, okay, so the stats are now updated by blk-throtl itself but
>
> > actually throttled. When the user does not add the throttle limit, the io
> > stats for cgroup v1 has nothing. I fix it according to the statistical
> > method of v2, and made it count all ios accurately.
>
> updated only when limits are configured which can be confusing. Makes sense
> to me. Can you please update the patch description accordingly?
>
> Also, the following change:
>
> @@ -2033,6 +2033,9 @@ void blk_cgroup_bio_start(struct bio *bio)
>          struct blkg_iostat_set *bis;
>          unsigned long flags;
>
> +       if (!cgroup_subsys_on_dfl(io_cgrp_subsys))
> +               return;
> +
>          /* Root-level stats are sourced from system-wide IO stats */
>          if (!cgroup_parent(blkcg->css.cgroup))
>                  return;
>
> seems incomplete as there's an additional
> cgroup_subsys_on_dfl(io_cgrp_subsys) test in the function. We probably wanna
> remove that?
>
> Thanks.

okay, according to your suggestion, I will send a v2.

Thanks