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Date: Tue, 06 Mar 2007 16:35:06 -0800
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Rusty Russell <rusty@rustcorp.com.au>
CC: Ingo Molnar <mingo@elte.hu>,
       lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Zachary Amsden <zach@vmware.com>,
       Jeremy Fitzhardinge <jeremy@xensource.com>,
       Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <ak@suse.de>
Subject: Re: [PATCH 8/8] Convert PDA into the percpu section
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Rusty Russell wrote:
> 	If we used __thread, then gcc could do this optimization for us when it
> knows an rvalue is needed, however:
>
> 1) gcc wants to use %gs, not %fs, which is measurably slower for the
> kernel,
> 2) gcc wants to use huge offsets to store the address of the per-cpu
> space, and this breaks Xen (and current lguest, but new lguest no longer
> uses segments for protection)
>   

Well, if we go to the effort of teaching gcc how to use %fs, we can
probably convince it to generate positive offset TLS relocs too.

    J