linux-kernel - Re: [patch 02/41] cpu alloc: The allocator

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Date:	Tue, 10 Jun 2008 20:05:18 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Mike Travis <travis@....com>, akpm@...ux-foundation.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch 02/41] cpu alloc: The allocator

Christoph Lameter a écrit :
> On Wed, 4 Jun 2008, Mike Travis wrote:
> 
>> I'm a bit confused.  Why is DEFINE_PER_CPU_SHARED_ALIGNED() conditioned on
>> ifdef MODULE?
>>
>>         #ifdef MODULE
>>         #define SHARED_ALIGNED_SECTION ".data.percpu"
>>         #else
>>         #define SHARED_ALIGNED_SECTION ".data.percpu.shared_aligned"
>>         #endif
>>
>>         #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
>>                 __attribute__((__section__(SHARED_ALIGNED_SECTION)))            \
>>                 PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name             \
>>                 ____cacheline_aligned_in_smp
> 
> Looks wrong to me. There can be shared objects even without modules.
> 
> 

Well, MODULE is not CONFIG_MODULES :)

If compiling an object that is going to be statically linked to kernel, 
MODULE is not defined, so we have shared objects.

When compiling a module, we cannot *yet* use .data.percpu.shared_aligned 
section, since module loader wont handle this section.

Alternative is to change modules linking for all arches to merge 
.data.percpu{*} subsections correctly, or tell module loader to take 
into account all .data.percpu sections.

AFAIK no module uses DEFINE_PER_CPU_SHARED_ALIGNED() yet...



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