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From: Chengming Zhou <zhouchengming@bytedance.com>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, duanxiongchun@bytedance.com,
	songmuchun@bytedance.com
Subject: Re: [Phishing Risk] Re: [Phishing Risk] [External] Re: [PATCH] blk-iocost: fix very large vtime when iocg activate
Date: Tue, 17 May 2022 09:39:14 +0800	[thread overview]
Message-ID: <1b0d20fb-ec92-6282-b8c3-4c0441ba4f8a@bytedance.com> (raw)
In-Reply-To: <YoL0RHmU4tbS2f/F@slm.duckdns.org>

On 2022/5/17 09:03, Tejun Heo wrote:
> On Tue, May 17, 2022 at 08:57:55AM +0800, Chengming Zhou wrote:
>> #define time_after64(a,b)	\
>> 	(typecheck(__u64, a) &&	\
>> 	 typecheck(__u64, b) && \
>> 	 ((__s64)((b) - (a)) < 0))
>> #define time_before64(a,b)	time_after64(b,a)
>>
>> I still don't get why my changes are wrong. :-)
> 
> It's a wrapping timestamp where a lower value doesn't necessarily mean
> earlier. The before/after relationship is defined only in relation to each
> other. Imagine a cirle representing the whole value range and picking two
> spots in the circle, if one is in the clockwise half from the other, the
> former is said to be earlier than the latter and vice-versa. vtime runs way
> faster than nanosecs and wraps regularly, so we can't use absolute values to
> compare before/after.

Please ignore my previous reply, you are right. I should fix the tracing
analysis tools to test again.

Thanks.

> 
> Thanks.
> 

      parent reply	other threads:[~2022-05-17  1:40 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-16  8:40 Chengming Zhou
2022-05-16 18:46 ` Tejun Heo
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 [this message]

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