Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] timers: fix offset calculation when the expires align
 with LVL_GRAN
To:     Thomas Gleixner <tglx@linutronix.de>
CC:     <john.stultz@linaro.org>, <sboyd@kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <1532669610-103892-1-git-send-email-xuyiping@hisilicon.com>
 <alpine.DEB.2.21.1807301234310.2518@nanos.tec.linutronix.de>
 <c68d9944-1fcc-dcd5-1e3d-07f979323b8c@hisilicon.com>
 <alpine.DEB.2.21.1807311616480.1610@nanos.tec.linutronix.de>
 <alpine.DEB.2.21.1807311633430.1610@nanos.tec.linutronix.de>
From:   Xu YiPing <xuyiping@hisilicon.com>
Message-ID: <86709eae-fa35-e36a-cafd-2c917d188276@hisilicon.com>
Date:   Wed, 1 Aug 2018 10:45:16 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.21.1807311633430.1610@nanos.tec.linutronix.de>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2018/7/31 22:34, Thomas Gleixner wrote:
> 
> 
> On Tue, 31 Jul 2018, Thomas Gleixner wrote:
> 
>> On Tue, 31 Jul 2018, Xu YiPing wrote:
>>> On 2018/7/30 19:03, Thomas Gleixner wrote:
>>>>
>>>> __internal_add_timer(base, timer)
>>>> {  
>>>>    idx = calc_wheel_index(1, 1)
>>>>        {
>>>>            delta = 1 - 1;	<-   0
>>>>
>>>>            if (0 < LVL_START(1))
>>>>                idx = calc_index(1, 0)
>>>>                     {
>>>>                         expires = (1 + LVL_GRAN(0) - 1) >> LVL_SHIFT(0);
>>>> 			----> expires = 0
>>> 			
>>> 			LVL_GRAN(0) = 1 and LVL_SHIFT(0) = 0
>>> 			
>>> 			after the calculation, expires = 1 ?
>>
>> Indeed. You're right. Math is hard... So the index would be 1 and still not
>> fulfil the below:
> 
> Hmm, crap. Let me think about it some more. 34C is way too hot to think.
> 

	when the expire is aligned with LVL_GRAN(x), it could be triggered at expire,
no need to wait another LVL_GRAN(x).

	just a little improvement, useful when expire is small.

> Thanks,
> 
> 	tglx
> 
> .
>