Message-ID: <47A35DDB.10002@zytor.com>
Date: Fri, 01 Feb 2008 09:58:51 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: dean gaudet <dean@arctic.org>
CC: Yi Yang <yi.y.yang@intel.com>, tglx@linutronix.de, mingo@redhat.com,
       linux-kernel@vger.kernel.org, akpm@linux-foundation.org
Subject: Re: [PATCH 2.6.24] x86: add sysfs interface for cpuid module
References: <1199441414.19185.9.camel@yangyi-dev.bj.intel.com>  <1201043126.3861.5.camel@yangyi-dev.bj.intel.com> <1201562058.12722.9.camel@yangyi-dev.bj.intel.com> <alpine.DEB.1.00.0802010830560.7110@twinlark.arctic.org> <47A35D55.8080708@zytor.com>
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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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