Re: 2.2.0pre1 OOPS on boot.
Linus Torvalds (torvalds@transmeta.com)
Wed, 30 Dec 1998 11:00:29 -0800 (PST)
On Wed, 30 Dec 1998, Alan Cox wrote:
>
> > - CONFIG_M386: Runs on anything
> > - CONFIG_M486: requires "invlpg" and a working supervisor mode WP bit
> > - CONFIG_M586: requires "rdtsc"
> > - CONFIG_M686: requires a non-broken local APIC when running SMP
> >
> > and now all machine configuration options actually have real meaning for
> > the behaviour of the kernel apart from just some alignment hints to the
> > compiler.
>
> The alignment hints are wrong for most non intel chips without RDTSC if you
> try and tie alignment to CPU info. The 'requires rdtsc' for 586+ isnt needed
> except for SMP systems - which are all intel for x86 so the problem doesn't
> arise for that case.
The "rdtsc" thing _is_ needed even for UP systems.
Look at the code generated for do_gettimeofday() some time - it's a
worthwhile optimization to do statically.
(And if you wonder why I care about gettimeofday(), just look at the
system call distribution for a lot of programs, including most X
programs).
As I mentioned in my email, it may be a valid thing to expand the choices
a bit (ie add a choice between i486 and i586), but the static "rdtsc"
thing definitely stays.
Linus
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