Re: [PATCH] blk-throttle: support io merge over iops_limit

[Yu Kuai]

Hi,

在 2025/03/12 3:34, Tejun Heo 写道:
> Hello,
>
> On Tue, Mar 11, 2025 at 11:08:00AM +0800, Yu Kuai wrote:
> ...
> > > That said, I'm not sure about changing the behavior now. blk-throtl has
> > > mostly used the number of bios as long as it has existed and given that
> > > there can be a signficant difference between the two metrics, I'm not sure
> > > the change is justified at this point.
> >
> > If we really concern about the behavior change, can we consider a new
> > flag that can switch to the old behavior? We'll see if any user will
> > complain.
>
> Yeah, that may be the right way to go about this, but let me turn this
> around and ask you why adding a new behavior would be a good idea. What
> problems are you trying to solve?

In the case of dirty pages writeback, BIO is 4k, while RQ can be up to
hw_sectors_kb. Our user are limiting iops based on real disk capacity
and they found BIO merge will be broken.

The idea way really is rq-qos based iops limit, which is after BIO merge
and BIO merge is ensured not borken. In this case, I have to suggest
them set a high iops limit or just remove the iops limit.

Thanks,
Kuai

> Thanks.