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

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Message-ID: <YQAydzEhZfPUpzWI@mtj.duckdns.org>
Date:   Tue, 27 Jul 2021 06:21:11 -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 27, 2021 at 11:06:18AM +0800, brookxu wrote:
> Make blk-throttle use rq-qos may be more elegant. But I found that there may be at least
> one problem that is difficult to solve. blk-throttle supports separate throttle for read
> and write IOs, which means that we cannot suspend tasks during throttle, but rq-qos
> throttle IOs by suspending tasks.

Ah, right, I forgot about that.

> We may be able to relocate the blk-throttle hooks to the rq-qos hooks. Since we may not
> be able to replace the throttle hook, in this case, if we register a rq-qos to the system,
> part of the blk-throttle hooks is in rq-qos and part hooks not, which feels a bit confusing.
> In addition, we may need to implement more hooks, such as IO merge hook.

Would it be possible to just move the blk-throtl throttling hook right next
to the rq-qos hook so that it gets throttled after splitting?

Thanks.

-- 
tejun