linux-kernel - Re: [PATCH 2.6.24] x86: add sysfs interface for cpuid module

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Message-ID: <47A35DDB.10002@zytor.com>
Date:	Fri, 01 Feb 2008 09:58:51 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	dean gaudet <dean@...tic.org>
CC:	Yi Yang <yi.y.yang@...el.com>, tglx@...utronix.de,
	mingo@...hat.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 2.6.24] x86: add sysfs interface for cpuid module

H. Peter Anvin wrote:
> dean gaudet wrote:
>> why do we need another kernel cpuid reading method when 
>> sched_setaffinity exists and cpuid is available in ring3?
> 
> Because /dev/cpu/*/cpuid:
> 
> a) predates sched_setaffinity by quite a few years
> b) is already widely used
> c) doesn't have issues with relative priorities (using sched_setaffinity
>    can easily wait forever.)
> d) can be accessed by unprivileged processes given appropriate device
>    info.
> 

(a) and (b) obviously doesn't apply to the proposed sysfs hack; nor does 
it give the administrator the control given by (d).  The sysfs hack is 
pointless.

	-hpa
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