linux-kernel - Re: [PATCH] optimize ktime_divns for constant divisors

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Message-ID: <87zjb4zdyc.fsf@free.fr>
Date:	Wed, 03 Dec 2014 21:16:27 +0100
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] optimize ktime_divns for constant divisors

Nicolas Pitre <nicolas.pitre@...aro.org> writes:

> Let ktime_divns() use do_div() inline whenever the divisor is constant
> and small enough.  This will make things like ktime_to_us() and 
> ktime_to_ms() much faster.

Hi Nicolas,

I suppose the "small enough" is linked to the "!(div >> 32)" in your patch.  Can
I have the rationale which brought up this value, and if that value is universal
across architectures (ie. x86/ppc/arm/...) ?

And when you say "much faster", do you have figures to add to your commit
message ?

Cheers.

--
Robert
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