Received-SPF: pass (google.com: domain of linux-kernel+bounces-214065-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Sender: Tejun Heo <htejun@gmail.com>
Date: Thu, 13 Jun 2024 12:32:04 -1000
From: Tejun Heo <tj@kernel.org>
To: Yu Kuai <yukuai1@huaweicloud.com>
Cc: josef@toxicpanda.com, axboe@kernel.dk, cgroups@vger.kernel.org,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com
Subject: Re: [PATCH -next 2/2] blk-throttle: fix lower control under super
 low iops limit
Message-ID: <ZmtzZKW1m6JpdfWx@slm.duckdns.org>
References: <20240513120848.2828797-1-yukuai1@huaweicloud.com>
 <20240513120848.2828797-3-yukuai1@huaweicloud.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240513120848.2828797-3-yukuai1@huaweicloud.com>

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