From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1LjX7B-0007m1-3q
	for qemu-devel@nongnu.org; Tue, 17 Mar 2009 07:05:45 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1LjX76-0007gg-7n
	for qemu-devel@nongnu.org; Tue, 17 Mar 2009 07:05:44 -0400
Received: from [199.232.76.173] (port=56572 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1LjX76-0007gd-0o
	for qemu-devel@nongnu.org; Tue, 17 Mar 2009 07:05:40 -0400
Received: from main.gmane.org ([80.91.229.2]:60976 helo=ciao.gmane.org)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <gceq-qemu-devel@m.gmane.org>)
	id 1LjX75-00033W-Iw
	for qemu-devel@nongnu.org; Tue, 17 Mar 2009 07:05:39 -0400
Received: from list by ciao.gmane.org with local (Exim 4.43)
	id 1LjX72-0004fT-NT
	for qemu-devel@nongnu.org; Tue, 17 Mar 2009 11:05:36 +0000
Received: from 141.76.6.219 ([141.76.6.219])
	by main.gmane.org with esmtp (Gmexim 0.1 (Debian))
	id 1AlnuQ-0007hv-00
	for <qemu-devel@nongnu.org>; Tue, 17 Mar 2009 11:05:36 +0000
Received: from usenet by 141.76.6.219 with local (Gmexim 0.1 (Debian))
	id 1AlnuQ-0007hv-00
	for <qemu-devel@nongnu.org>; Tue, 17 Mar 2009 11:05:36 +0000
From: Steffen Liebergeld <usenet@gmx.eu>
Date: Tue, 17 Mar 2009 11:05:24 +0000 (UTC)
Message-ID: <gpo05k$6u4$1@ger.gmane.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: news <news@ger.gmane.org>
Subject: [Qemu-devel] branches are expensive
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

Hi,

while measuring the execution of an ARM guest, I encountered that branches are
extremely expensive in terms of executed host instructions. A single ARM
branch takes 148 to 152 host instructions. In my setup host and guest use the
ARM instruction set architecture.

My question is what makes branches so expensive? What code is run when
executing a branch? Other instructions are translated to 14 to 40
instructions.

Any help is appreciated.

Greetings, Steffen