linux-kernel - Re: [PATCH] blk-throtl: optimize IOPS throttle for large IO scenarios

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Date:   Mon, 26 Jul 2021 11:46:39 -1000
From:   Tejun Heo <tj@...nel.org>
To:     brookxu <brookxu.cn@...il.com>
Cc:     axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-throtl: optimize IOPS throttle for large IO scenarios

Hello,

On Tue, Jul 20, 2021 at 12:35:54AM +0800, brookxu wrote:
> In order to avoid code duplication and IOPS stability problems caused by estimating
> the equivalent number of IOs, and to avoid potential deadlock problems caused by
> synchronization through queue_lock. I tried to count the number of splited IOs in
> the current window through two atomic counters. Add the value of the atomic variable
> when calculating io_disp[rw], which can also avoid the problem of inaccurate IOPS in
> large IO scenarios. How do you think of this approach? Thanks for your time.

I guess it's okay but am still not a big fan of adding another hook. This is
primarily because blk-throtl is sitting too early in the stack - e.g. rq_qos
is doing the same thing but sits after the split path - and it's a bit nasty
to add an additional hook for it.

Do you think it can be an option to relocate the blk-throtl hooks to the
same spots as rq-qos or, even better, make it use rq-qos?

Thanks.

-- 
tejun