Message-ID: <4383597E.7060300@didntduck.org>
Date: Tue, 22 Nov 2005 12:46:38 -0500
From: Brian Gerst <bgerst@didntduck.org>
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To: Andi Kleen <ak@suse.de>
CC: Benjamin LaHaise <bcrl@kvack.org>, linux-kernel@vger.kernel.org
Subject: Re: rfc/rft: use r10 as current on x86-64
References: <20051122165204.GG1127@kvack.org> <20051122171040.GY20775@brahms.suse.de>
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Andi Kleen wrote:
> On Tue, Nov 22, 2005 at 11:52:04AM -0500, Benjamin LaHaise wrote:
>> Hello Andi et al,
>>
>> The patch below converts x86-64 to use r10 as the current pointer instead 
>> of gs:pcurrent.  This results in a ~34KB savings in the code segment of 
>> the kernel.  I've tested this with running a few regular applications, 
>> plus a few 32 bit binaries.  If this patch is interesting, it probably 
>> makes sense to merge the thread info structure into the task_struct so 
>> that the assembly bits for syscall entry can be cleaned up.  Comments?
> 
> I think you could get most of the benefit by just dropping
> the volatile and "memory" from read_pda(). With that gcc would
> usually CSE current into a register and it would would work essentially
> the same way with only minor more .text overhead, but r10 would be still
> available.

It seems that GCC is reluctant to use the extended registers anyways 
because of the rex prefix, so I don't think dedicating r10 to current 
will cause that many problems.

--
				Brian Gerst
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