linux-kernel - Re: Linux 3.1-rc9

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Message-ID: <4E9C917B.2050802@zytor.com>
Date:	Mon, 17 Oct 2011 13:35:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Simon Kirby <sim@...tway.ca>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: Linux 3.1-rc9

On 10/17/2011 11:49 AM, Ingo Molnar wrote:
> Do we have some hard data on this, which we could put into comments 
> in include/linux/ktime.h and such? Older versions of GCC used to do a 
> bad job of long long handling on 32-bit systems - that might be a 
> factor in the performance figures.
> 
> But i suspect you are right that the cost is still very much there 

64/64 division is done bit by bit on most (all?) 32-bit architectures.

64/32 division can be done in hardware on some architectures, e.g. x86.

	-hpa
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