From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1KJZAN-00040q-LS
	for qemu-devel@nongnu.org; Thu, 17 Jul 2008 15:29:27 -0400
Received: from [199.232.76.173] (port=34174 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1KJZAN-00040i-7m
	for qemu-devel@nongnu.org; Thu, 17 Jul 2008 15:29:27 -0400
Received: from mx1.polytechnique.org ([129.104.30.34]:50369)
	by monty-python.gnu.org with esmtps
	(TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60)
	(envelope-from <fabrice@bellard.org>) id 1KJZAM-0001vh-S4
	for qemu-devel@nongnu.org; Thu, 17 Jul 2008 15:29:27 -0400
Received: from fbe1.dev.netgem.com (gw.netgem.com [195.68.2.34])
	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by ssl.polytechnique.org (Postfix) with ESMTP id 59EC23316C
	for <qemu-devel@nongnu.org>; Thu, 17 Jul 2008 21:29:25 +0200 (CEST)
Message-ID: <487F9D94.5080507@bellard.org>
Date: Thu, 17 Jul 2008 21:29:24 +0200
From: Fabrice Bellard <fabrice@bellard.org>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: [RFC][PATCH] x86: CS limit checks
References: <487F3393.3040609@siemens.com> <487F51E1.9070102@bellard.org>
	<487F73AE.50509@siemens.com>
In-Reply-To: <487F73AE.50509@siemens.com>
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org

[...]
> And then there is the open question how much performance can be gained
> with compile-time optimization for those guests who do use segmentation.

The goal is to optimize the cases where segmentation is not used ! It is 
just an extension of the existing "HF_ADDSEG" optimization.

> The worst case is very roughly about 50% slowdown right now (/w vs. w/o
> -seg-checks). As answered privately, some -no-seg-checks switch could
> remain a useful optimization.

Not sure. I believe most recent OSes (i.e. those where speed really 
matters) have segment registers loaded so that no runtime checks are 
necessary.

Fabrice.