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

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Message-ID: <73c1f2160901270450hb27a1e8ya4ea298b2e601dc9@mail.gmail.com>
Date:	Tue, 27 Jan 2009 07:50:23 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 #tj-percpu] x86: fix build breakage on voyage

On Tue, Jan 27, 2009 at 6:47 AM, Tejun Heo <htejun@...il.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?

I thought about ways to make the early percpu code more general, but
with only three current users, any solution seemed to be overkill.
What I can do is eliminate the pointers and use a single flag to mark
the early maps as dead.

--
Brian Gerst
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