Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.35 as permitted sender) client-ip=23.128.96.35;
Date:   Thu, 5 Oct 2023 19:04:14 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Li Nan <linan666@huaweicloud.com>
Cc:     Khazhy Kumykov <khazhy@chromium.org>, tj@kernel.org,
        josef@toxicpanda.com, axboe@kernel.dk, yukuai3@huawei.com,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        houtao1@huawei.com, yangerkun@huawei.com
Subject: Re: [PATCH] blk-throttle: Calculate allowed value only when the
 throttle is enabled
Message-ID: <20231005170413.GB32420@redhat.com>
References: <20230928015858.1809934-1-linan666@huaweicloud.com>
 <CACGdZY+JV+PdiC_cspQiScm=SJ0kijdufeTrc8wkrQC3ZJx3qQ@mail.gmail.com>
 <4ace01e8-6815-29d0-70ce-4632818ca701@huaweicloud.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4ace01e8-6815-29d0-70ce-4632818ca701@huaweicloud.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Precedence: bulk

sorry, didn't notice this part before.

I am not a asm expert (to say at least;) but

On 10/05, Li Nan wrote:
>
> When (a * mul) overflows, a divide 0 error occurs in
> mul_u64_u64_div_u64().

Just in case... No, iirc it is divq which triggers #DE when the
result of division doesn't fit u64.

(a * mul) can't overflow, the result is 128-bit rax:rdx number.

Oleg.