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

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Message-ID: <alpine.LFD.1.10.0809081056350.3117@nehalem.linux-foundation.org>
Date:	Mon, 8 Sep 2008 11:04:30 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	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

On Mon, 8 Sep 2008, H. Peter Anvin wrote:
>  
>  config X86_GENERIC
> -	bool "Generic x86 support"
> +	bool "Generic x86 support" if EMBEDDED

Ok, so after having realized that this seems to be more about a bug with 
gcc, I'm really not as convinced any more.

As far as I can tell, there are three issues:

 - "-mtune=core/core2/pentium4/.." is buggy in some gas/gcc versions on 
   x86-32, and makes architectural choices.

   Any actual _released_ versions? Maybe it's just a current SVN issue?

   Workaround: don't use it. And yes, X86_GENERIC=y will do that, although 
   quite frankly that seems to be dubious in itself. But quite frankly, 
   it's a gcc bug, and we should see it as such.

   The better workaround may well be "-Wa,-mtune=generic" as you pointed 
   out.

 - We do the CONFIG_P6_NOPL thing ourselves, and we should just stop 
   doing that on 32-bit. There simply isn't a good enough reason to do so. 
   I already posteed the Kconfig.cpu patch to just stop doing it.

 - X86_GENERIC means _other_ things too, like doing a 128-bit cacheline 
   just so that it won't suck horribly on P4's even if it's otherwise 
   tuned for a good microarchitecture.

And they really do seem to be _separate_ issues. Do we really want to tie 
these things together under X86_GENERIC? 

		Linus
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