From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KyRuf-0001HQ-Vd for qemu-devel@nongnu.org; Fri, 07 Nov 2008 09:02:14 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KyRuf-0001Gm-96 for qemu-devel@nongnu.org; Fri, 07 Nov 2008 09:02:13 -0500 Received: from [199.232.76.173] (port=60506 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KyRuf-0001GX-34 for qemu-devel@nongnu.org; Fri, 07 Nov 2008 09:02:13 -0500 Received: from yx-out-1718.google.com ([74.125.44.153]:47819) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KyRue-00074Y-KX for qemu-devel@nongnu.org; Fri, 07 Nov 2008 09:02:12 -0500 Received: by yx-out-1718.google.com with SMTP id 3so468358yxi.82 for ; Fri, 07 Nov 2008 06:02:12 -0800 (PST) Message-ID: <49144A61.9030708@codemonkey.ws> Date: Fri, 07 Nov 2008 08:02:09 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] vga slow with -enable-kvm References: <491407E9.4040506@redhat.com> In-Reply-To: <491407E9.4040506@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Gerd Hoffmann wrote: > Hi, > > The vga display is very slow when using latest svn with kvm enabled. > Just try to boot any linux kernel with vesafb enabled (vga=0x314 for > 800x600@16), enjoy watching the boot messages scroll. Booting without > kvm enabled is *faster*. > Yeah, this is why we need the VGA optimization. A tight MMIO loop in QEMU is actually pretty efficient. No code translation is needed so it ends up being a pretty straight forward set of calls to the MMIO handler function. It's hugely expensive in KVM though because you have to take a huge number of vmexits and they're pretty expensive. Anyway, the VGA optimization will fix this nicely. Regards, Anthony Liguori