From: Tejun Heo <tj@kernel.org>
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, duanxiongchun@bytedance.com,
songmuchun@bytedance.com
Subject: Re: [PATCH] blk-iocost: fix very large vtime when iocg activate
Date: Mon, 16 May 2022 08:46:07 -1000 [thread overview]
Message-ID: <YoKb7wpkz3xoCS6s@slm.duckdns.org> (raw)
In-Reply-To: <20220516084045.96004-1-zhouchengming@bytedance.com>
On Mon, May 16, 2022 at 04:40:45PM +0800, Chengming Zhou wrote:
> When the first iocg activate after blk_iocost_init(), now->vnow
> maybe smaller than ioc->margins.target, cause very large vtarget
> since it's u64.
>
> vtarget = now->vnow - ioc->margins.target;
> atomic64_add(vtarget - vtime, &iocg->vtime);
>
> Then the iocg's vtime will be very large too, larger than now->vnow.
It's a wrapping counter. Please take a look at how time_before64() and
friends work.
Nacked-by: Tejun Heo <tj@kernel.org>
Again, please spend more effort understanding the code before sending these
subtle patches.
Thanks.
--
tejun
next prev parent reply other threads:[~2022-05-16 18:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-16 8:40 [PATCH] blk-iocost: fix very large vtime when iocg activate Chengming Zhou
2022-05-16 18:46 ` Tejun Heo [this message]
2022-05-17 0:57 ` [Phishing Risk] [External] " Chengming Zhou
2022-05-17 1:03 ` Tejun Heo
2022-05-17 1:23 ` [Phishing Risk] " Chengming Zhou
2022-05-17 1:39 ` Chengming Zhou
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