linux-kernel - Re: [PATCH] blk-throttle: fix repeat limit on bio with BIO_BPS

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Message-ID: <fbf135e8-de16-8eb4-9ade-1b979a335e33@huaweicloud.com>
Date: Mon, 22 Apr 2024 11:47:41 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: 周泰宇 <zhoutaiyu@...ishou.com>,
 Yu Kuai <yukuai1@...weicloud.com>, "tj@...nel.org" <tj@...nel.org>
Cc: "josef@...icpanda.com" <josef@...icpanda.com>,
 "axboe@...nel.dk" <axboe@...nel.dk>,
 "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
 "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] blk-throttle: fix repeat limit on bio with
 BIO_BPS_THROTTLED

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