linux-kernel - Re: [PATCH 0/3] percpu: Optimize percpu accesses

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Date:	Thu, 24 Jan 2008 16:17:44 -0800
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen <ak@...e.de>,
	Christoph Lameter <clameter@....com>, jeremy@...p.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] percpu: Optimize percpu accesses

Ingo Molnar wrote:
> * travis@....com <travis@....com> wrote:
> 
>> This patchset provides the following:
>>
>>   * Generic: Percpu infrastructure to rebase the per cpu area to zero
>>
>>     This provides for the capability of accessing the percpu variables
>>     using a local register instead of having to go through a table
>>     on node 0 to find the cpu-specific offsets.  It also would allow
>>     atomic operations on percpu variables to reduce required locking.
>>
>>   * x86_64: Fold pda into per cpu area
>>
>>     Declare the pda as a per cpu variable. This will move the pda
>>     area to an address accessible by the x86_64 per cpu macros.
>>     Subtraction of __per_cpu_start will make the offset based from
>>     the beginning of the per cpu area.  Since %gs is pointing to the
>>     pda, it will then also point to the per cpu variables and can be
>>     accessed thusly:
>>
>> 	%gs:[&per_cpu_xxxx - __per_cpu_start]
>>
>>   * x86_64: Rebase per cpu variables to zero
>>
>>     Take advantage of the zero-based per cpu area provided above. Then 
>>     we can directly use the x86_32 percpu operations. x86_32 offsets 
>>     %fs by __per_cpu_start. x86_64 has %gs pointing directly to the 
>>     pda and the per cpu area thereby allowing access to the pda with 
>>     the x86_64 pda operations and access to the per cpu variables 
>>     using x86_32 percpu operations.
> 
> tried it on x86.git and 1/3 did not build and 2/3 causes a boot hang 
> with the attached .config.
> 
> 	Ingo
> 

The build error was fixed with the note I sent to you yesterday with a
"fixup" patch for changes in -mm but not in x86.git (attached).

I'll try out your config next.

Thanks,
Mike



View attachment "zero-based-x86.git-fix" of type "text/plain" (582 bytes)