From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1IY1am-0008EL-RB
	for qemu-devel@nongnu.org; Wed, 19 Sep 2007 11:35:56 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1IY1al-0008E2-Nn
	for qemu-devel@nongnu.org; Wed, 19 Sep 2007 11:35:55 -0400
Received: from [199.232.76.173] (helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1IY1al-0008Dz-If
	for qemu-devel@nongnu.org; Wed, 19 Sep 2007 11:35:55 -0400
Received: from mail.codesourcery.com ([65.74.133.4])
	by monty-python.gnu.org with esmtps
	(TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1IY1al-0003lm-4W
	for qemu-devel@nongnu.org; Wed, 19 Sep 2007 11:35:55 -0400
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Fwd: Re: [Qemu-devel] [PATCH] SVM support]
Date: Wed, 19 Sep 2007 16:35:49 +0100
References: <1190148856.14938.247.camel@rapid>
	<00FC6422-CB9E-4C8D-9B27-C77A072A1234@suse.de>
	<1190212770.12194.16.camel@jma4.dev.netgem.com>
In-Reply-To: <1190212770.12194.16.camel@jma4.dev.netgem.com>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200709191635.51270.paul@codesourcery.com>
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, l_indien@magic.fr
Cc: Alexander Graf <agraf@suse.de>

> > >> OK, great. Having 64 bits may also help for additional (ie future...)
> > >> features in PowerPC 64 emulation.
> > >
> > > Maybe worth letting the target say whether it needs 32 or 64-bit
> > > flags.
> > > The flag lookup is likely to be on a hot path.
> > >
>
> I may be wrong, but it seems to me that TB flags are only used to be
> compared in tb_find_fast and tb_find_slow, which are not a very fast
> path (we come here when we cannot jump directly to the next tb and are
> not in the most time critical code) then we can afford adding a few asm
> instructions (I would say max 2 ?) to replace a 32 bits comparison with
> a 64 bits one. My feeling is that the performance loss here won't be
> sensible, but that may need to be proved.

For some reason I thought the flags were also used in the hash lookup. This is 
not the case, so I withdraw my objection.

Paul