Received-SPF: pass (google.com: domain of linux-kernel+bounces-152709-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Subject: Re: [PATCH] blk-throttle: fix repeat limit on bio with
 BIO_BPS_THROTTLED
To: =?UTF-8?B?5ZGo5rOw5a6H?= <zhoutaiyu@kuaishou.com>,
 Yu Kuai <yukuai1@huaweicloud.com>, "tj@kernel.org" <tj@kernel.org>
Cc: "josef@toxicpanda.com" <josef@toxicpanda.com>,
 "axboe@kernel.dk" <axboe@kernel.dk>,
 "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
 "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 "yukuai (C)" <yukuai3@huawei.com>
References: <20240419120747.38031-1-zhoutaiyu@kuaishou.com>
 <ea781ccc-c29e-894e-c54a-f44ea349edca@huaweicloud.com>
 <e2d291e6b6ed43d89930eb2a7d459ff8@kuaishou.com>
From: Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <fbf135e8-de16-8eb4-9ade-1b979a335e33@huaweicloud.com>
Date: Mon, 22 Apr 2024 11:47:41 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
Precedence: bulk
MIME-Version: 1.0
In-Reply-To: <e2d291e6b6ed43d89930eb2a7d459ff8@kuaishou.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit

Hi!

在 2024/04/22 11:33, 周泰宇 写道:
> What I want to do here was to set an easy to reach value to BPS_LIMIT (10M/s in this example) and an unable to reach value to IOPS_LIMIT (100000 in this example).
> 
> 
> Under this setting, the iostat shows that the bps is far less than 10M/s and sometimes is far larger than 10M/s.

Yes, I know this behaviour, and this is because blk-throttle works
before IO split, and io stats is accounting bps for rq-based disk after
IO split, if you using Q2C for bps you'll see that bps is stable as
limit.

Hi, Tejun！

Do you think this *phenomenon* need to be fixed? If so, I don't see a
easy way other than throttle bio after *IO split*. Perhaps ohter than
bio merge case, this can be another motivation to move blk-throttle to
rq_qos_throttle().

Thanks,
Kuai