From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42739) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TCStE-00046j-WB for qemu-devel@nongnu.org; Fri, 14 Sep 2012 06:12:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TCStC-0003xC-AJ for qemu-devel@nongnu.org; Fri, 14 Sep 2012 06:12:48 -0400 Received: from goliath.siemens.de ([192.35.17.28]:24023) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TCStC-0003wu-0h for qemu-devel@nongnu.org; Fri, 14 Sep 2012 06:12:46 -0400 Message-ID: <5053031B.8020902@siemens.com> Date: Fri, 14 Sep 2012 12:12:43 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <5052DF3A.1070007@msgid.tls.msk.ru> <20120914093304.GC6819@redhat.com> <5052FB60.3060109@msgid.tls.msk.ru> <50530047.9030703@siemens.com> <5053010E.1000103@msgid.tls.msk.ru> In-Reply-To: <5053010E.1000103@msgid.tls.msk.ru> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] qemu-system-i386 vs qemu-system-x86_64 ? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Tokarev Cc: qemu-devel On 2012-09-14 12:03, Michael Tokarev wrote: > On 14.09.2012 14:00, Jan Kiszka wrote: > [] >> The major difference in qemu-system-i386 vs. qemu-system-x86_64 is on >> the TCG side: We measured noticeable performance benefits when running >> 32/16 bit OSes against qemu-system-i386 vs. using qemu-system-x86_64. I >> don't have numbers at hand, but colleagues decided to use the 32-bit >> version for that reason (when no KVM is available). > > Interesting. Maybe someone should look at the difference on TCG side > and merge interesting bits from i386 to x86_64... :) I suppose the difference - for our use cases at least - lies in the different register and address sizes. Maybe there is room for more runtime optimizations, we never looked in that details as -i386 still works fine. And, if you are on 32-bit host (see below) - but we aren't, qemu-system-x86_64 hurts even more. > > The thing is: x86_64 becomes the only x86 platform these days, or at > least the MAIN platform. I know, and I'm telling everyone. Still, too many crazy people keep on installing 32-bit distros or even 32-bit kernels. Maybe x64-32 will improve this. > > Thank you for the clarification -- very useful information indeed! > > /mjt > You are welcome. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux