linux-kernel - Re: [PATCH 1/2] jiffies: Allow CLOCK_TICK

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Message-ID: <500DA7EB.1030608@linaro.org>
Date:	Mon, 23 Jul 2012 12:37:15 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Ingo Molnar <mingo@...nel.org>
CC:	lkml <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] jiffies: Allow CLOCK_TICK_RATE to be undefined

On 07/19/2012 02:37 AM, Ingo Molnar wrote:
> * John Stultz <john.stultz@...aro.org> wrote:
>
>> From: Catalin Marinas <catalin.marinas@....com>
...
>> diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
>> index 265e2c3..a2134be 100644
>> --- a/include/linux/jiffies.h
>> +++ b/include/linux/jiffies.h
>> @@ -39,9 +39,6 @@
>>   # error Invalid value of HZ.
>>   #endif
>>   
>> -/* LATCH is used in the interval timer and ftape setup. */
>> -#define LATCH  ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
>> -
>>   /* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
>>    * improve accuracy by shifting LSH bits, hence calculating:
>>    *     (NOM << LSH) / DEN
>> @@ -54,8 +51,15 @@
>>   #define SH_DIV(NOM,DEN,LSH) (   (((NOM) / (DEN)) << (LSH))              \
>>                                + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
>>   
>> +#ifdef CLOCK_TICK_RATE
>> +/* LATCH is used in the interval timer and ftape setup. */
>> +#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
>> +
>>   /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
>>   #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
>> +#else
>> +#define ACTHZ (HZ << 8)
>> +#endif
> The ACTHZ naming ugliness slipped past me. 'ACT' can mean so
> many things - please improve it to something more obvious, like
> 'REAL_HZ' or 'KERNEL_HZ'.

ACTHZ has been around for a while. ~2002 I think?

Is it ok if I do the rename in a following patch?

> Also, we tend to write such #if/#else/#endif patterns as:
>
> #if FOO
> # define BAR
> #else
> # define BAZ
> #endif
I'll fix this.

Thanks for the review
-john

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