From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [Qemu-devel] Re: [PATCH v2] qemu-kvm: Speed up of the dirty-bitmap-traveling Date: Wed, 10 Feb 2010 17:54:29 +0100 Message-ID: <4B72E4C5.5050803@suse.de> References: <4B728FF9.6010707@lab.ntt.co.jp> <4B72B28E.6010801@redhat.com> <4B72D69D.7050005@codemonkey.ws> <4B72D838.9060603@suse.de> <4B72E051.8090008@codemonkey.ws> <4B72E224.1090901@suse.de> <4B72E2D2.7010701@redhat.com> <4B72E32F.3080205@suse.de> <4B72E430.4070700@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , OHMURA Kei , mtosatti@redhat.com, "qemu-devel@nongnu.org" , "kvm@vger.kernel.org" , Anthony Liguori To: Avi Kivity Return-path: Received: from cantor2.suse.de ([195.135.220.15]:55876 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753672Ab0BJQye (ORCPT ); Wed, 10 Feb 2010 11:54:34 -0500 In-Reply-To: <4B72E430.4070700@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > On 02/10/2010 06:47 PM, Alexander Graf wrote: > >>>> Because on PPC, you usually run PPC32 userspace code on a PPC64 kernel. >>>> Unlike with x86, there's no real benefit in using 64 bit userspace. >>>> >>>> >>>> >>>> >>> btw, does 32-bit ppc qemu support large memory guests? It doesn't on >>> x86, and I don't remember any hacks to support large memory guests >>> elsewhere. >>> >>> >>> >> It doesn't :-). In fact, the guest we virtualize wouldn't work with > 2 >> GB anyways, because that needs an iommu implementation. >> >> > > Oh, so you may want to revisit the "there's no real benefit in using 64 > bit userspace". > Well, for normal users they don't. SLES11 is 64-bit only, so we're good on that. But openSUSE uses 32-bit userland. > Seriously, that looks like a big deficiency. What would it take to > implement an iommu? > > I imagine Anthony's latest patches are a first step in that journey. > All reads/writes from PCI devices would need to go through a wrapper. Maybe we could also define a per-device offset for memory accesses. That way the overhead might be less. Yes, Anthony's patches look like they are a really big step in that direction. Alex