Re: [BUG] x86 kenel won't boot under Virtual PC



On Mon, 8 Sep 2008, H. Peter Anvin wrote:

The help text is indeed out of date. I did a patch yesterday to, among other
things, update it; I also want to verify that we are disabling all options
that can cause gcc or binutils to generate nopl's; I plan to push it today.

Peter.

The help text may be out of date because of changes to NOPL usage, but you
should ask yourself whether the change is actually a _good_ change.

IOW, I really don't see why you are pushing changing the help-text,
instead of just making the kernel work better.

The fact that some broken gcc/binutils versions may screw us over _anyway_
may well mean that we should just push back on _that_ change instead.

Quite frankly, from a user perspective, even a very _technical_ one,
please tell me what the advantage of not being fairly generic by default
is. Really.

Yes, there are some _big_ ISA issues where it is worth doing real static
code selection (as opposed to just instruction selection and scheduling
etc that still _works_ for everybody, but optimizes for certain
archtiectures).

So things like cmpxchg/xadd (for atomics) and cmov (for compiler-generated
code), and bswap (for networking) can really make a big difference, and
are not really realistic to do dynamically.

But NOPL? That's simply not _worth_ it being painful over.

And the fact is, the current help text describes

(a) the historical meaning (optimize for a specific architecture, but
don't make extreme choices that are bad for others)
(b) what people would generally _want_.

and I really don't think that changing the help text is the right solution
here. It may be "technically correct", but it is simply not user-friendly
or smart.

Linus
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