linux-kernel - Re: [PATCH 1/3] Fix COW D-cache aliasing on fork

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Date:	Fri, 20 Oct 2006 17:38:32 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	Ralf Baechle <ralf@...ux-mips.org>
cc:	David Miller <davem@...emloft.net>, nickpiggin@...oo.com.au,
	akpm@...l.org, linux-kernel@...r.kernel.org, anemo@....ocn.ne.jp,
	linux-arch@...r.kernel.org, schwidefsky@...ibm.com,
	James.Bottomley@...elEye.com
Subject: Re: [PATCH 1/3] Fix COW D-cache aliasing on fork

On Sat, 21 Oct 2006, Ralf Baechle wrote:
>
> > That said, maybe nobody does that. Virtual caches are a total braindamage 
> > in the first place, so hopefully they have limited use.
> 
> On MIPS we never had pure virtual caches.

Ok, so on MIPS my schenario doesn't matter.

I think (but may be mistaken) that ARM _does_ have pure virtual caches 
with a process ID, but people have always ended up flushing them at 
context switch simply because it just causes too much trouble.

Sparc? VIPT too? Davem?

I have absolutely zero clue about s390.

Anyway, it sounds to me like this is too big to decide for 2.6.19 anyway, 
and as far as I can tell this i snot a regression, right? Ie we've always 
had the aliasing issue. Ralf?

But it would be good to have something for the early -rc1 sequence for 
2.6.20, and maybe the MIPS COW D$ patches are it, if it has performance 
advantages on MIPS that can also be translated to other virtual cache 
users..

> Be sure I'm sending a CPU designers a strong message about aliases.

Castration. That's the best solution. We don't want those people 
procreating.

			Linus
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