linux-kernel - Re: [PATCH] timers: fix offset calculation when the expires align with LVL

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Message-ID: <86709eae-fa35-e36a-cafd-2c917d188276@hisilicon.com>
Date:   Wed, 1 Aug 2018 10:45:16 +0800
From:   Xu YiPing <xuyiping@...ilicon.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <john.stultz@...aro.org>, <sboyd@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] timers: fix offset calculation when the expires align
 with LVL_GRAN



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
> 
> .
>