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From: Keith Owens <kaos@ocs.com.au>
To: Ingo Molnar <mingo@elte.hu>
cc: David.Mosberger@acm.org, Andrew Morton <akpm@osdl.org>,
       "Chen, Kenneth W" <kenneth.w.chen@intel.com>,
       linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org
Subject: Re: Add prefetch switch stack hook in scheduler function
In-reply-to: Your message of "Thu, 28 Jul 2005 09:41:18 +0200."
             <20050728074118.GA20581@elte.hu>
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Date: Thu, 28 Jul 2005 18:09:08 +1000
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On Thu, 28 Jul 2005 09:41:18 +0200,
Ingo Molnar <mingo@elte.hu> wrote:
>
>* david mosberger <dmosberger@gmail.com> wrote:
>
>> Also, should this be called prefetch_stack() or perhaps even just
>> prefetch_task()?  Not every architecture defines a switch_stack
>> structure.
>
>yeah. I'd too suggest to call it prefetch_stack(), and not make it a
>macro & hook but something defined on all arches, with for now only ia64
>having any real code in the inline function.
>
>i'm wondering, is the switch_stack at the same/similar place as
>next->thread_info? If yes then we could simply do a
>prefetch(next->thread_info).

No, they can be up to 30K apart.  See include/asm-ia64/ptrace.h.
thread_info is at ~0xda0, depending on the config.  The switch_stack
can be as high as 0x7bd0 in the kernel stack, depending on why the task
is sleeping.