linux-kernel - Re: [PATCH 2/3 V2] time: allow gcc to fold constants when using

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Date:	Wed, 22 Apr 2015 14:00:07 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Nicholas Mc Guire <hofrat@...dl.org>
cc:	Michal Marek <mmarek@...e.cz>,
	Masahiro Yamada <yamada.m@...panasonic.com>,
	Sam Ravnborg <sam@...nborg.org>,
	"H. Peter Alvin" <hpa@...or.com>, Joe Perches <joe@...ches.com>,
	John Stultz <john.stultz@...aro.org>,
	Andrew Hunter <ahh@...gle.com>, Paul Turner <pjt@...gle.com>,
	Aaron Sierra <asierra@...-inc.com>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3 V2] time: allow gcc to fold constants when using

On Sun, 12 Apr 2015, Nicholas Mc Guire wrote:
> +extern unsigned long __msecs_to_jiffies(const unsigned int m);
> +#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
> +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> +{

This should move the comments explaining the logic for each variant as
well.

> +		return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
> +}
> +#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
> +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> +{
> +		if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> +			return MAX_JIFFY_OFFSET;
> +		return m * (HZ / MSEC_PER_SEC);
> +}
> +#else
> +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> +{
> +		if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> +			return MAX_JIFFY_OFFSET;
> +
> +		return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> +			>> MSEC_TO_HZ_SHR32;
> +}
> +#endif
> +static inline unsigned long msecs_to_jiffies(const unsigned int m)
> +{
> +	if (__builtin_constant_p(m)) {
> +		if ((int)m < 0)
> +			return MAX_JIFFY_OFFSET;
> +		return _msecs_to_jiffies(m);
> +	} else
> +		return __msecs_to_jiffies(m);

It'd be nice to have this as two patches:

1) Factor out the code into inline helpers w/o adding anything

2) Add the __builtin_constant_p() check

Thanks,

	tglx
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