linux-kernel - Re: [PATCH 13/17] x86-64: Remove pda

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Message-ID: <4972BE69.2000609@kernel.org>
Date:	Sun, 18 Jan 2009 14:30:17 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/17] x86-64: Remove pda_init()

Brian Gerst wrote:
> On Sat, Jan 17, 2009 at 11:32 PM, Tejun Heo <tj@...nel.org> wrote:
>> Hello,
>>
>> Brian Gerst wrote:
>>> -void __cpuinit pda_init(int cpu)
>>> -{
>>> -     struct x8664_pda *pda = cpu_pda(cpu);
>>> -
>>> -     /* Setup up data that may be needed in __get_free_pages early */
>>> -     loadsegment(fs, 0);
>>> -     loadsegment(gs, 0);
>>> -
>>> -     load_pda_offset(cpu);
>>> -}
>> Simply removing these should work fine as they're also initialized in
>> other places earlier but I think they still need to be in cpu_init()
>> because...
>>
>> /*
>>  * cpu_init() initializes state that is per-CPU. Some data is already
>>  * initialized (naturally) in the bootstrap process, such as the GDT
>>  * and IDT. We reload them nevertheless, this function acts as a
>>            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>  * 'CPU state barrier', nothing should get across.
>>  * A lot of state is already set up in PDA init for 64 bit
>>  */
> 
> That comment seems like overkill.  It may have been relevant in an
> earlier time, but I don't think we need to be so strict now,
> especially for things we know are set properly in head_xx.S.

That may be so, but wouldn't such change deserve a separate patch with
accompanying update in the comment?  It's not simple move from A to B
change.

Thanks.

-- 
tejun
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