Re: [PATCH 1/2 #tj-percpu] x86: fix build breakage on voyage

Ingo Molnar
2009-01-27T13:11:24Z

* Tejun Heo <htejun@gmail.com> wrote:

> Hello, Ingo.
>
> Ingo Molnar wrote:
> >> +#ifdef CONFIG_X86_LOCAL_APIC
> >> early_per_cpu_ptr(x86_cpu_to_apicid) = NULL;
> >> early_per_cpu_ptr(x86_bios_cpu_apicid) = NULL;
> >> +#endif
> >
> > That patch is not acceptable - it is ugly and it adds another set of
> > #ifdefs to an already complex piece of code.
>
> Well, although the patch itself does add #ifdef, if you look over the
> whole series, voyager is now a much more conforming citizen in the x86
> world. There are several solutions to this particular one.
>
> 1. Just let apic stuff defined and not use it in voyager if the ifdef
> is disturbing. IIUC, apic isn't used in voyager at all, right?
>
> 2. Clean up early percpu stuff so that it each early percpu variable
> doesn't need to be explicitly copied and cleared, which is the
> actual problem here.
>
> 3. But, then again, the current interim and ugly way of doing it isn't
> too bad considering the small number of early per cpu users.
>
> To me the current form doesn't look too bad but if it's too ugly, maybe
> doing #2 is not such a bad idea such that early percpu can be
> transferred to percpu in more systematic way. It still feels a bit like
> overdoing it tho.
>
> What do you think?

This issue might be minor, but it's the death of a thousand cuts. It
should switch to the generic x86 code, use smp_ops to wrap/express its own
SMP weirdnesses [and extend it where needed - because _that_ is a step
forward for the whole code - fixing build bugs isnt] and then such
problems simply wont occur.

Ingo