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Message-ID: <20090415140959.GD12760@elte.hu>
Date: Wed, 15 Apr 2009 16:09:59 +0200
From: Ingo Molnar <mingo@...e.hu>
To: David Howells <dhowells@...hat.com>,
Jeremy Fitzhardinge <jeremy@...p.org>,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, 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()
* David Howells <dhowells@...hat.com> wrote:
> > There's three too 'thick' headers: linux/percpu.h,
> > linux/prefetch.h and asm/processor.h.
>
> Yes, I noticed.
>
> linux/percpu.h needs to be split three ways for instance:
> definitions, access methods, and alocators.
yeah. Often a super-header has to be split into several basic
headers or header pairs.
> linux/prefetch.h isn't too bad: what it needs is the prefetch
> stuff splitting out of asm/processor.h into asm/prefetch.h.
yeah.
> > Please create include/linux/percpu_types.h for basic data types
> > and simple, self-sufficient primitives. Also have an
> > include/linux/percpu_api.h or include/linux/percpu.h include
> > file for convenience/speedup inlines. The latter will only be
> > included in .c files, where 'combination' of type spaces is not
> > a problem.
>
> Not so. The problem is that various header files make use of
> per-cpu variable accessors (asm/current.h and asm/thread_info.h to
> name a couple) to build inline asm.
Hm, what portion did you mark with 'not so'?
inline asm is used in inline functions there, and that is what
'instantiates' the types in a 'mixed' manner and way below their
proper hierarchic level as well - creating both a mess and, as mess
increases above a critical threshold an inevitable circular
dependency as well.
> Anyway, here are a pair of patches on top of the one I've already
> sent to Linus. The second breaks a number of header files into
> pieces and rearranges the percpu headers to put the DECLARE and
> DEFINE macros together.
>
> The first patch could potentially be applied immediately. It adds
> #inclusions and forward refs that are required to iron out compile
> errors from the second patch.
>
> Note that these only work for the configuration I routinely use on
> my x86_64 test machine. It will break all other arches and many
> other i386 and x86_64 configurations.
I dont disagree, but i'd like to warn that such patches need _way_
more testing, these are never same-day obvious patches.
We have split up one big x86 header in this development cycle
(asm/pgtable.h) and that alone was highly non-trivial and needed
about a week to settle down, even with intense development and
testing.
Ingo
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