linux-kernel - Re: [PATCH v7 4/9] blk-throttle: fix io hung due to configuration updates

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Date:   Wed, 17 Aug 2022 07:52:45 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     mkoutny@...e.com, axboe@...nel.dk, ming.lei@...hat.com,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v7 4/9] blk-throttle: fix io hung due to configuration
 updates

On Wed, Aug 17, 2022 at 09:30:30AM +0800, Yu Kuai wrote:
> > Would it be easier if the fields were signed? It's fragile and odd to
> > explain "these are unsigned but if they underflow they behave just like
> > signed when added" when they can just be signed. Also, I have a hard time
> > understand what "preempt" means above.
> 
> I think preempt shound never happen based on current FIFO
> implementation, perhaps

Can you elaborate what "preempt" is?

> > > +	if (bps_limit != U64_MAX)
> > > +		tg->bytes_skipped[rw] +=
> > > +			calculate_bytes_allowed(bps_limit, jiffy_elapsed) -
> > > +			tg->bytes_disp[rw];
> > > +	if (iops_limit != UINT_MAX)
> > > +		tg->io_skipped[rw] +=
> > > +			calculate_io_allowed(iops_limit, jiffy_elapsed) -
> > > +			tg->io_disp[rw];
> > 
> > So, this is calculating the budgets to carry over. Can we name them
> > accordingly? I don't know what "skipped" means.
> 
> Yeah, thanks for you advice, art of naming is a little hard for me...
> How do you think about these name: extended_bytes/io_budget?

How about carryover_{ios|bytes}?

Thanks.

-- 
tejun