linux-kernel - Re: [PATCH 1/4] Zero based percpu: Infrastructure to rebase the per cpu area to zero

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Date:	Tue, 10 Jun 2008 12:06:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] Zero based percpu: Infrastructure to rebase the
	per cpu area to zero


* Mike Travis <travis@....com> wrote:

>     * Support an option
> 
> 	CONFIG_HAVE_ZERO_BASED_PER_CPU
> 
>       to make offsets for per cpu variables to start at zero.
> 
>       If a percpu area starts at zero then:
> 
> 	-  We do not need RELOC_HIDE anymore
> 
> 	-  Provides for the future capability of architectures providing
> 	   a per cpu allocator that returns offsets instead of pointers.
> 	   The offsets would be independent of the processor so that
> 	   address calculations can be done in a processor independent way.
> 	   Per cpu instructions can then add the processor specific offset
> 	   at the last minute possibly in an atomic instruction.
> 
>       The data the linker provides is different for zero based percpu segments:
> 
> 	__per_cpu_load	-> The address at which the percpu area was loaded
> 	__per_cpu_size	-> The length of the per cpu area
> 
>     * Removes the &__per_cpu_x in lockdep. The __per_cpu_x are already
>       pointers. There is no need to take the address.
> 
>     * Updates kernel/module.c to be able to deal with a percpu area that
>       is loaded at __per_cpu_load but is accessed at __per_cpu_start.
> 
> Based on linux-2.6.tip

applied to tip/core/percpu, thanks.

	Ingo
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