linux-kernel - Re: [PATCH] FRV: Fix the section attribute on UP DECLARE_PER

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Date:	Wed, 15 Apr 2009 18:49:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] FRV: Fix the section attribute on UP DECLARE_PER_CPU()


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, 15 Apr 2009, David Howells wrote:
> > Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > 
> > > Hmm. Why not move it all above the '#include <asm/percpu.h>'?
> > 
> > There are circular dependencies between the x86 arch headers that both use
> > this and are used to implement this, and it's a bit fragile.
> 
> Grr. Indeed it seems to be. Nasty. Header files seem to want that 
> DECLARE_PER_CPU() thing without all the other baggage that is 
> implied by including all of <linux/percpu.h>, so they just include 
> <asm/percpu.h> directly instead.
> 
> What a mess.
> 
> So maybe we could move DEFINE_PER_CPU in there too? It's less than 
> perfect, but at least we'd have things together rather than split 
> in really odd ways.

I think splitting the type related defines away into percpu_types.h, 
and updating the lowlevel headers to include linux/percpu_types.h 
[which would include asm/percpu.h] would do the trick.

Even the exising percpu.h could be made lighter:

slab.h:    is needed for the kzalloc in the !SMP wrapper case. That 
           could be eliminated by uninlining the UP wrappers.

preempt.h: is needed for preempt_disable/enable() in the 
           get_cpu_var()/put_cpu_var() methods.

smp.h:     not sure what it's needed for - nothing obvious at first
           sight.

Most of them could be eliminated.

	Ingo
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