Re: [PATCH -next 2/2] blk-throttle: fix lower control under super low iops limit

[Yu Kuai]

Hi,

在 2024/06/14 6:32, Tejun Heo 写道:
> Hello,
>
> On Mon, May 13, 2024 at 08:08:48PM +0800, Yu Kuai wrote:
> ...
> > However, if limit is quite low, the result can be 0, then
> > allowed IO in the slice is 0, this will cause missing dispatch and
> > control will be lower than limit.
> >
> > For example, set iops_limit to 5 with HD disk, and test will found that
> > iops will be 3.
>
> Hmm... can't this be solved by starting the next slice with the right
> credit?

Of course, this looks like feasible. I'll look into this.
> >   static unsigned int tg_throtl_slice(struct throtl_grp *tg, int rw)
> >   {
> > +	if (tg->throtl_slice[rw])
> > +		return tg->throtl_slice[rw];
> >   	return tg->td->throtl_slice;
>
> Because this is a bit nasty. If we want to use difference throttling slices
> for different cgroups, we might as well do it universally.

I do thought about this, however, because different cgroups have
different slice start, I convinced myself this is fine to have different
slice as well.

Thanks,
Kuai

> Thanks.