Re: [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled

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To: Li Nan <linan666@xxxxxxxxxxxxxxx>
Subject: Re: [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Date: Thu, 5 Oct 2023 19:04:14 +0200
Cc: Khazhy Kumykov <khazhy@xxxxxxxxxxxx>, tj@xxxxxxxxxx, josef@xxxxxxxxxxxxxx, axboe@xxxxxxxxx, yukuai3@xxxxxxxxxx, cgroups@xxxxxxxxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, yi.zhang@xxxxxxxxxx, houtao1@xxxxxxxxxx, yangerkun@xxxxxxxxxx
In-reply-to: <4ace01e8-6815-29d0-70ce-4632818ca701@huaweicloud.com>
References: <20230928015858.1809934-1-linan666@huaweicloud.com> <CACGdZY+JV+PdiC_cspQiScm=SJ0kijdufeTrc8wkrQC3ZJx3qQ@mail.gmail.com> <4ace01e8-6815-29d0-70ce-4632818ca701@huaweicloud.com>
User-agent: Mutt/1.5.24 (2015-08-30)

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.

Follow-Ups:
- Re: [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled
  - From: Khazhy Kumykov

References:
- [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled
  - From: linan666
- Re: [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled
  - From: Khazhy Kumykov

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