linux-kernel - Re: [tip:timers/core] ntp: Fix integer overflow when setting time

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Message-ID: <4F63516E.90602@zytor.com>
Date:	Fri, 16 Mar 2012 07:42:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	mingo@...hat.com, levinsasha928@...il.com,
	linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:timers/core] ntp: Fix integer overflow when setting time

On 03/16/2012 02:48 AM, Thomas Gleixner wrote:
>>
>> Perhaps we should use the same kind of multiply-and-shift tricks we're
>> doing for jiffies conversion?  If nothing else it ought to perform better.
> 
> It's not a hotpath where performance matters, but divide by zero does :)

Doing the inverse multiply wouldn't have a divide by zero problem.  What
perhaps is more important (and the reason we went to shift-multiply) is
that in addition to being faster, it also avoids unnnecessary overflows.
 I would really like to figure out how to do proper shift-multiply for
the 64-bit jiffy conversions too.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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