linux-kernel - Re: [git pull] x86 fixes

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Date:	Mon, 8 Sep 2008 21:02:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	x86 maintainers <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [git pull] x86 fixes

* H. Peter Anvin <hpa@...or.com> wrote:

> Arjan van de Ven wrote:
>>
>> the ideal case would be "support them all"
>
> Not really.  That would include things like the i386, which is a bunch 
> of really nasty stuff.

agreed - especially the verify_area() impact makes it a non-starter.

but 486 and higher is certainly quite reasonable, and is still being 
tested.

... and _in practice_ 99% of all systems that run Linux today understand 
CMOV.

... _and_ in practice 99% of all new Linux systems shipped today are 
Core2 or better.

... and so on it goes with this argument. Everyone has a different 
target audience and there's no firm limit. Maybe what makes more sense 
is to have some sort of time dependency:

  support all x86 CPUs released in the last year
  support all x86 CPUs released in the past 5 years
  support all x86 CPUs released in the past 10 years
  support all x86 CPUs released ever
  [ ... or configure a specific model ]

and people/distributions would use _those_ switches. That means we could 
continuously tweak those targets, as systems become obsolete and new 
CPUs arrive.

	Ingo
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