linux-kernel - Re: [PATCH] x86: pat cpu feature bit setting for known cpus

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Date:	Tue, 25 Mar 2008 16:01:14 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	suresh.b.siddha@...el.com
Subject: Re: [PATCH] x86: pat cpu feature bit setting for known cpus

H. Peter Anvin wrote:
> Ingo Molnar wrote:
>> * Venki Pallipadi <venkatesh.pallipadi@...el.com> wrote:
>>
>>>>>  OK, note previous question: what is the motivation for having 
>>>>>  this as a whitelist (as opposed to a blacklist)?
>>>> Venkatesh could tell?
>>> Main reason for white-list at this point is not to be side-tracked by 
>>> real or potential erratas on older CPUs. Focussing on getting the 
>>> support for this feature on current and future CPUs. If older CPUs 
>>> have survived all these days without this feature, they should be 
>>> doing OK.
>>
>> well, the upside would be that since most testing of Linux kernels is 
>> done on _old_ hardware (people tend to risk their old hw first ;-), 
>> we'd get faster convergence of the codebase, even though we have the 
>> risk of erratas (known and unknown ones alike). Code that artificially 
>> limits its utility is almost always slow to stabilize.
>>
> 
> Yes, using a whitelist of this type is wrong, IMO, and smells faintly of 
> vendor-lockin.
> 

By the way, I want to clarify: I didn't mean it was *intended* as 
vendor-lockin, just that it's an undesirable effect of this.

	-hpa
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