Message-ID: <450510E0.8080906@goop.org>
Date: Mon, 11 Sep 2006 00:31:44 -0700
From: Jeremy Fitzhardinge <jeremy@goop.org>
User-Agent: Thunderbird 1.5.0.5 (X11/20060907)
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To: Ingo Molnar <mingo@elte.hu>
CC: Andrew Morton <akpm@osdl.org>, Andi Kleen <ak@suse.de>,
       Laurent Riffard <laurent.riffard@free.fr>,
       Arjan van de Ven <arjan@infradead.org>,
       Kernel development list <linux-kernel@vger.kernel.org>,
       Jeremy Fitzhardinge <jeremy@xensource.com>
Subject: Re: 2.6.18-rc6-mm1: GPF loop on early boot
References: <20060908011317.6cb0495a.akpm@osdl.org> <200609101032.17429.ak@suse.de> <20060910115722.GA15356@elte.hu> <200609101334.34867.ak@suse.de> <20060910132614.GA29423@elte.hu> <20060910093307.a011b16f.akpm@osdl.org> <450499D3.5010903@goop.org> <20060911051028.GA10084@elte.hu>
In-Reply-To: <20060911051028.GA10084@elte.hu>
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Ingo Molnar wrote:
> another thing about i386-pda: why did you pick the %gs selector to store 
> the PDA in? %fs would be a better choice because %gs is used by glibc so 
> the saving/restoring of %fs would likely be near zero-cycles cost. 
> (instead of the current 9 cycles for saving/restoring %gs)
>   

Why would saving/restoring %fs be quicker?  The main reason I chose %gs 
was so that it didn't add anything to the context switch time (since %gs 
needed to be switched anyway), and it leaves open the possibility of 
using gcc's TLS support in the kernel (I have a working demonstration of 
this, but Rusty and I are still working out the module details).

    J
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