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

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Date:	Wed, 15 Nov 2006 20:03:08 +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:
> > 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.)
> >   
> 
> Well, in that case they probably don't care whether the kernel uses 
> %fs or %gs ;)
> 
> But either way, this doesn't have much bearing on Eric's test; we'd be 
> only talking about a few ns per kernel exit, rather than 5% for 
> read/write.

if the timings are different then it very much has bearing on the 
argument that i made against the current i386 PDA patchset, that mixed 
use segments are suboptimal.

So i'm NAK-ing the i386 PDA patchset until this has been properly 
measured (and fixed if needed).

	Ingo
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