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Message-ID: <alpine.LFD.1.10.0809050931340.3117@nehalem.linux-foundation.org>
Date: Fri, 5 Sep 2008 09:39:38 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Jan Beulich <jbeulich@...ell.com>
cc: linux@...dersweb.net, Ingo Molnar <mingo@...e.hu>,
Andi Kleen <andi-suse@...stfloor.org>,
Arjan van de Ven <arjan@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] x86 kenel won't boot under Virtual PC
On Fri, 5 Sep 2008, Jan Beulich wrote:
>
> I disagree here: If I configure a 686+ kernel, I expect these NOPs to be
> that way (and to work). If you want to run on something that's not
> compliant, you just shouldn't configure your kernel that way.
Well, if you actually do a
git grep 'ASM_NOP[0-9]'
you'll find that just the _definitions_ of those things are the bulk of it
BY FAR, and that there doesn't seem to be a single user that cares even
remotely about performance.
So I actually think that the whole thing is a waste of time. We should
probably
- pick a single set of NOP's per 32-bit/64-bit (since the good nops in
32-bit aren't 64-bit instructions at all, so we do want different nops
depending on _that_)
The whole static choice by microarchitecture is pure garbage.
- Probably also just declare that those default nops are single
instructions, just so that we never even have to think about it from a
dynamic replacement angle.
Look at the uses again, and realize that it really is just pure garbage
to have this kind of complex and subtle stuff going on.
- Move the optimized nop definitions (K7_NOPx etc) to the only place that
cares - asm/x86/kernel/alternative.c. When we do things _dynamically_,
it can actually make sense to pick a nop more precisely, but for this
whole static thing it's just a pain.
IOW, if it actually _worked_ reasonably, I wouldn't care. But clearly it
doesn't. And once it's not working reasonably, it should be fixed.
Linus
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