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Subject: Re: [PATCH RESEND v6 4/8] blk-throttle: fix io hung due to config
 updates
To:     =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>,
        Tejun Heo <tj@kernel.org>
Cc:     Yu Kuai <yukuai1@huaweicloud.com>, axboe@kernel.dk,
        ming.lei@redhat.com, cgroups@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
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From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <0bbf3d0c-88c4-8120-3df3-960dda041864@huaweicloud.com>
Date:   Thu, 28 Jul 2022 18:34:44 +0800
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Hi

在 2022/07/28 17:33, Michal Koutný 写道:
> On Wed, Jul 27, 2022 at 08:39:19AM -1000, Tejun Heo <tj@kernel.org> wrote:
>> I'm not quiet sure this is correct. What if the limit keeps changing across
>> different values? Then we'd be calculating the skipped amount based on the
>> last configuration only which would be incorrect.
> 
> When one change of configuration is correct, then all changes must be
> correct by induction. It's sufficient to take into account only the one
> old config and the new one.
> 
> This __tg_update_skipped() calculates bytes_skipped with the limit
> before the change and bytes_skipped are used (divided by) the new limit
> in tg_with_in_bps_limit().
> The accumulation of bytes_skipped across multiple changes (until slice
> properly ends) is proportional to how bytes_allowed would grow over
> time.
> That's why I find this correct (I admit I had to look back into my
> notes when this was first discussed).
> 
> HTH,
> Michal
> 

Hi, Tejun

Michal already explain it very well, please let me know if you still
thinks there are better ways.

Thanks,
Kuai