linux-kernel - Re: [rfc 08/45] cpu alloc: x86 support

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Date:	Mon, 26 Nov 2007 23:12:52 -0500
From:	John Richard Moser <nigelenki@...cast.net>
To:	Andi Kleen <ak@...e.de>
CC:	Christoph Lameter <clameter@....com>, akpm@...ux-foundation.org,
	travis@....com, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 08/45] cpu alloc: x86 support



Andi Kleen wrote:
> On Tuesday 20 November 2007 04:50, Christoph Lameter wrote:
>> On Tue, 20 Nov 2007, Andi Kleen wrote:

> You could in theory move the modules, but then you would need to implement
> a full PIC dynamic linker for them  first and also increase runtime overhead
> for them because they would need to use a GOT/PLT.

On x86-64?  The GOT/PLT should stay in cache due to temporal locality. 
The x86-64 instruction set itself handles GOT-relative addressing rather 
well; what's a 1% loss on x86 is like 0.01% on x86-64, so I'm thinking 
100 times better?

I think I got this by `-fpic -pie` compiling nbyte benchmark versus 
fixed position, each with and without on 32-bit (which made about a 1% 
difference) and on 64-bit (which made a 0.01% difference).  It was a 
long time ago.

Still, yeah I know.  Complexity.

(You have the ability to textrel these things too, and just rewrite 
non-PIC, depending on how you feel about that)
-- 
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