Messages in this thread | | | Date | Fri, 5 Sep 2008 09:39:38 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [BUG] x86 kenel won't boot under Virtual PC |
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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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