linux-kernel - Re: [PATCH -next 2/2] blk-throttle: fix lower control under super low iops limit

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Message-ID: <ZmtzZKW1m6JpdfWx@slm.duckdns.org>
Date: Thu, 13 Jun 2024 12:32:04 -1000
From: Tejun Heo <tj@...nel.org>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: josef@...icpanda.com, axboe@...nel.dk, cgroups@...r.kernel.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH -next 2/2] blk-throttle: fix lower control under super
 low iops limit

Hello,

On Mon, May 13, 2024 at 08:08:48PM +0800, Yu Kuai wrote:
...
> However, if limit is quite low, the result can be 0, then
> allowed IO in the slice is 0, this will cause missing dispatch and
> control will be lower than limit.
> 
> For example, set iops_limit to 5 with HD disk, and test will found that
> iops will be 3.

Hmm... can't this be solved by starting the next slice with the right
credit?

>  static unsigned int tg_throtl_slice(struct throtl_grp *tg, int rw)
>  {
> +	if (tg->throtl_slice[rw])
> +		return tg->throtl_slice[rw];
>  	return tg->td->throtl_slice;

Because this is a bit nasty. If we want to use difference throttling slices
for different cgroups, we might as well do it universally.

Thanks.

-- 
tejun