linux-kernel - Re: [PATCH V5 05/17] blk-throttle: add upgrade logic for LIMIT

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Date:   Mon, 9 Jan 2017 14:46:00 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Shaohua Li <shli@...com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, axboe@...com, vgoyal@...hat.com
Subject: Re: [PATCH V5 05/17] blk-throttle: add upgrade logic for LIMIT_LOW
 state

Hello, again.

On Mon, Jan 09, 2017 at 01:40:53PM -0500, Tejun Heo wrote:
> I think it'd be great to explain the above.  It was a bit difficult
> for me to follow.  It's also interesting because we're tying state
> transitions for both read and write together.  blk-throtl has been
> handling reads and writes independently, now the mode switching from
> low to max is shared across reads and writes.  I suppose it could be
> fine but would it be complex to separate them out?  It's weird to make
> this one state shared across reads and writes while not for others or
> was this sharing intentional?

I thought more about it and as the low limit is regulated by latency,
it makes sense to make the state shared across reads and writes;
otherwise, IOs in one direction could easily mess up the other
direction.  Can you please document that this is an intentional design
and explain the rationale tho?

Thanks.

-- 
tejun