linux-kernel - Re: i386 PDA patches use of %gs

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Date:	Wed, 15 Nov 2006 19:49:36 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Arjan van de Ven <arjan@...radead.org>, akpm@...l.org, ak@...e.de,
	linux-kernel@...r.kernel.org, Michael.Fetterman@...cam.ac.uk,
	Ian Campbell <Ian.Campbell@...Source.com>
Subject: Re: i386 PDA patches use of %gs


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Ingo Molnar wrote:
> > but it does not actually use the 'normal usermode TLS selector' - it 
> > only loads it.
> >
> > a meaningful test would be to allocate two selector values and load and 
> > read+write memory through both of them.
> >   
> 
> Well, obviously in one case it would need to switch between 
> null/non-null/null.  But yes, good point about using the "usermode" 
> %gs each iteration.  I'll do some more tests.

i'd not even use glibc's %gs but set up two separate selectors. (that's 
a more controlled experiment - someone might run a non-TLS glibc, etc.)

	Ingo
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