From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1O4Vm8-0005xV-6x for qemu-devel@nongnu.org; Wed, 21 Apr 2010 04:59:16 -0400 Received: from [140.186.70.92] (port=44795 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1O4Vm6-0005uu-6Y for qemu-devel@nongnu.org; Wed, 21 Apr 2010 04:59:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1O4Vm4-0005WD-J7 for qemu-devel@nongnu.org; Wed, 21 Apr 2010 04:59:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40516) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1O4Vm4-0005W3-8N for qemu-devel@nongnu.org; Wed, 21 Apr 2010 04:59:12 -0400 Message-ID: <4BCEBE5C.4020404@redhat.com> Date: Wed, 21 Apr 2010 11:59:08 +0300 From: Avi Kivity MIME-Version: 1.0 References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: QEMU-KVM and video performance List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerhard Wiesinger Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org On 04/19/2010 10:14 PM, Gerhard Wiesinger wrote: > Hello, > > Finally I got QEMU-KVM to work but video performance under DOS is very > low (QEMU 0.12.3 stable and QEMU GIT master branch is fast, QEMU KVM > is slow) > > I'm measuring 2 performance critical video performance parameters: > 1.) INT 10h, function AX=4F05h (set same window/set window/get window) > 2.) Memory performance to segment page A000h > > So BIOS performance (which might be port performance to VGA > index/value port) is about factor 5 slower, memory performance is > about factor 100 slower. > > QEMU 0.12.3 and QEMU GIT performance is the same (in the measurement > tolerance) and listed only once, QEMU KVM is much more slower (details > see below). > > Test programs can be provided, source code will be release soon. > > Any ideas why KVM is so slow? 16-color vga is slow because kvm cannot map the framebuffer to the guest (writes are not interpreted as RAM writes). 256+-color vga should be fast, except when switching the vga window. Note it's only fast on average, the first write into a page will be slow as kvm maps it in. Which mode are you using? > Any ideas for improvement? Currently when the physical memory map changes (which is what happens when the vga window is updated), kvm drops the entire shadow cache. It's possible to do this only for vga memory, but not easy. -- error compiling committee.c: too many arguments to function