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Message-ID: <0bbf3d0c-88c4-8120-3df3-960dda041864@huaweicloud.com>
Date: Thu, 28 Jul 2022 18:34:44 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Michal Koutný <mkoutny@...e.com>,
Tejun Heo <tj@...nel.org>
Cc: Yu Kuai <yukuai1@...weicloud.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 RESEND v6 4/8] blk-throttle: fix io hung due to config
updates
Hi
在 2022/07/28 17:33, Michal Koutný 写道:
> On Wed, Jul 27, 2022 at 08:39:19AM -1000, Tejun Heo <tj@...nel.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
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