linux-kernel - Re: [GIT RFC] percpu: use dynamic percpu allocator as the default percpu allocator

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Date:	Thu, 2 Apr 2009 13:13:41 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
Cc:	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	Paul Mundt <lethal@...ux-sh.org>, rmk@....linux.org.uk,
	starvik@...s.com, ralf@...ux-mips.org, davem@...emloft.net,
	cooloney@...nel.org, kyle@...artin.ca, matthew@....cx,
	grundler@...isc-linux.org, takata@...ux-m32r.org,
	benh@...nel.crashing.org, rth@...ddle.net,
	heiko.carstens@...ibm.com
Subject: Re: [GIT RFC] percpu: use dynamic percpu allocator as the default
 percpu allocator

On Thu, 2 Apr 2009 11:24:18 +0400
Ivan Kokshaysky <ink@...assic.park.msu.ru> wrote:

> On the other hand, some tricks with DEFINE_PER_CPU() are indeed possible -
> for instance, using weak references we could force the compiler to
> generate proper addressing mode. So DEFINE_PER_CPU(int, foo) in module
> would expand to something like this:
> 
> 	extern int per_cpu__foo;
> 	asm(".weakref per_cpu__foo, per_cpu_mod__foo");
> 	__attribute__((__section__(".data.percpu"))) int per_cpu_mod__foo
> 
> The main problem is that our DEFINE_PER_CPU() macro consists of more
> than one definition, so it won't be possible to specify both storage class
> and initializer with it.
> 
> If it's acceptable to change the semantics from
> 
> static DEFINE_PER_CPU(int, foo) = 1
> 
> to
> 
> DEFINE_PER_CPU(static, int, foo) = 1
> 
> then we're ok.
> 
> Or maybe just add STATIC_DEFINE_PER_CPU_xx() variants?

That is what I'm after as well. Just drop the "static" from the
DEFINE_PER_CPU statement found inside modules and it works.

My experiments with the weak and visibility attribute failed because
the static storage class specifier together with the attribute either
causes a compile error or static just overrides the attribute.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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