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Date: Thu, 19 Dec 2002 14:26:38 -0800
From: "H. Peter Anvin" <hpa@transmeta.com>
Organization: Transmeta Corporation
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To: Linus Torvalds <torvalds@transmeta.com>
CC: Jamie Lokier <lk@tantalophile.demon.co.uk>, bart@etpmod.phys.tue.nl,
       davej@codemonkey.org.uk, terje.eggestad@scali.com, drepper@redhat.com,
       matti.aarnio@zmailer.org, hugh@veritas.com, mingo@elte.hu,
       linux-kernel@vger.kernel.org
Subject: Re: Intel P6 vs P7 system call performance
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Linus Torvalds wrote:
> 
> Uli's suggested glibc approach is to just put the magis system call 
> address (which glibc gets from the AT_SYSINFO elf aux table entry) into 
> the per-thread TLS area, which is alway spointed to by %gs anyway.
>
> THIS WORKS WITH ALL DSO'S WITHOUT ANY GAMES, ANY MMAP'S, ANY RELINKING, OR
> ANY EXTRA WORK AT ALL!
> 
> The system call entry becomes a simple
> 
> 	call *%gs:constant-offset
> 
> Not mmap. No magic system calls. No relinking. Not _nothing_. One 
> instruction, that's it. 
> 

Unfortunately it means taking an indirect call cost for every invocation...

	-hpa

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