From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47867) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e6HAU-0006Ao-3E for qemu-devel@nongnu.org; Sun, 22 Oct 2017 10:23:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e6HAP-00040x-5Y for qemu-devel@nongnu.org; Sun, 22 Oct 2017 10:23:58 -0400 Received: from mail1.hostfission.com ([139.99.139.48]:41008) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e6HAO-0003z7-Qj for qemu-devel@nongnu.org; Sun, 22 Oct 2017 10:23:53 -0400 Received: from www1.hostfission.com (www1.hostfission.com [139.99.139.52]) by mail1.hostfission.com (Postfix) with ESMTP id E93DE422A1 for ; Sun, 22 Oct 2017 21:47:57 +1100 (AEDT) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Sun, 22 Oct 2017 21:47:57 +1100 From: geoff@hostfission.com Message-ID: <088c92d5c3be0715c46f20e8b0ba0a0f@hostfission.com> Subject: [Qemu-devel] PCI Passthrough + AMD + NPT List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Hi All, I have started to dig into why ntp seems to slow down graphics performance on AMD systems using PCI passthrough and figured I would report what I have so far discovered. I have noted the primary point of failure seems to be specifically with PhysX. This is why people only see a slow down in certain games, not everything uses PhysX. Using FluidMark[1] the problem is immediately obvious, showing extremely low FPS on light/medium workloads with ntp enabled, and extreme fluididy and high FPS with ntp disabled. Switching nVidia to use CPU makes no difference to the performance when ntp is enabled, which seems to indicate that PhysX is falling back to CPU due to a failure of some kind to initialize. With ntp turned off, and nVidia set to use the CPU for PhysX I see an identical performance drop off in FluidMark as I see when ntp is enabled, this would seem to confirm this suspicion. Since other features such as APIC is only available if ntp is enabled, it could be something down stream of ntp that is getting disabled as a consequence of turning off ntp. It might be interesting to see if we can get some diagnostics information out of PhysX to see what if any error or debugging information it might provide when it falls back to CPU. 1: http://www.geeks3d.com/20130308/fluidmark-1-5-1-physx-benchmark-fluid-sph-simulation-opengl-download/ Kind Regards, Geoffrey McRae