linux-kernel - Re: [PATCH -next v5 4/8] blk-throttle: fix io hung due to config updates

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Message-ID: <75b3cdcc-1aa3-7259-4900-f09a2a081716@huawei.com>
Date:   Sat, 25 Jun 2022 16:36:34 +0800
From:   Yu Kuai <yukuai3@...wei.com>
To:     Michal Koutný <mkoutny@...e.com>, <tj@...nel.org>
CC:     <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>
Subject: Re: [PATCH -next v5 4/8] blk-throttle: fix io hung due to config
 updates

在 2022/06/24 0:26, Michal Koutný 写道:
> On Thu, Jun 23, 2022 at 08:27:11PM +0800, Yu Kuai <yukuai3@...wei.com> wrote:
>>> Here we may allow to dispatch a bio above current slice's
>>> calculate_bytes_allowed() if bytes_skipped is already >0.
>>
>> Hi, I don't expect that to happen. For example, if a bio is still
>> throttled, then old slice is keeped with proper 'bytes_skipped',
>> then new wait time is caculated based on (bio_size - bytes_skipped).
>>
>> After the bio is dispatched(I assum that other bios can't preempt),
> 
> With this assumptions it adds up as you write. I believe we're in
> agreement.
> 
> It's the same assumption I made below (FIFO everywhere, i.e. no
> reordering). So the discussed difference shouldn't really be negative
> (and if the assumption didn't hold, so the modular arithmetic yields
> corerct bytes_skipped value).
Yes, nice that we're in aggreement.

I'll wait to see if Tejun has any suggestions.

Thanks,
Kuai
> 
> Michal
> .
>