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

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Date:   Fri, 19 Aug 2022 07:33:22 -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,
        "yukuai3@...wei.com >> yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v7 4/9] blk-throttle: fix io hung due to configuration
 updates

Hello,

On Thu, Aug 18, 2022 at 09:16:28AM +0800, Yu Kuai wrote:
> 在 2022/08/18 1:52, Tejun Heo 写道:
> > 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?
> 
> Here preempt means that the bio that is throttled later somehow get
> dispatched earlier, Michal thinks it's better to comment that the code
> still works fine in this particular scenario.

You'd have to spell it out. It's not clear "preempt" means the above.

> > How about carryover_{ios|bytes}?
> 
> Yes, that sounds good.
> 
> By the way, should I use 'ios' here instead of 'io'? I was confused
> because there are many places that is using 'io' currently.

Yeah, blk-throttle.c is kinda inconsistent about that. It uses bytes/ios in
some places and bytes/io in others. I'd prefer ios here.

Thanks.

-- 
tejun