From: "H. Peter Anvin" <hpa@zytor.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: mingo@redhat.com, levinsasha928@gmail.com,
linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:timers/core] ntp: Fix integer overflow when setting time
Date: Fri, 16 Mar 2012 07:42:54 -0700 [thread overview]
Message-ID: <4F63516E.90602@zytor.com> (raw)
In-Reply-To: <alpine.LFD.2.02.1203161047220.2466@ionos>
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.
next prev parent reply other threads:[~2012-03-16 14:43 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-15 16:36 [PATCH 1/2] math: Introduce div64_long Sasha Levin
2012-03-15 16:36 ` [PATCH 2/2] ntp: Fix integer overflow when setting time Sasha Levin
2012-03-15 21:53 ` [tip:timers/core] " tip-bot for Sasha Levin
2012-03-16 1:29 ` H. Peter Anvin
2012-03-16 9:48 ` Thomas Gleixner
2012-03-16 14:42 ` H. Peter Anvin [this message]
2012-03-15 21:52 ` [tip:timers/core] math: Introduce div64_long tip-bot for Sasha Levin
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