From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39661) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1brRBi-00061Z-M9 for qemu-devel@nongnu.org; Tue, 04 Oct 2016 10:59:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1brRBe-00028P-81 for qemu-devel@nongnu.org; Tue, 04 Oct 2016 10:59:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52290) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1brRBd-000288-Tr for qemu-devel@nongnu.org; Tue, 04 Oct 2016 10:59:18 -0400 Date: Tue, 4 Oct 2016 15:59:11 +0100 From: "Daniel P. Berrange" Message-ID: <20161004145911.GA2155@redhat.com> Reply-To: "Daniel P. Berrange" References: <1472736127-18137-1-git-send-email-marcel@redhat.com> <6c9103e7-70ad-55c6-5533-d6d9bbaa39b4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6c9103e7-70ad-55c6-5533-d6d9bbaa39b4@redhat.com> Subject: Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laszlo Ersek Cc: Marcel Apfelbaum , qemu-devel@nongnu.org, Peter Maydell , Drew Jones , mst@redhat.com, Andrea Bolognani , Alex Williamson , Gerd Hoffmann , Laine Stump On Mon, Sep 05, 2016 at 06:24:48PM +0200, Laszlo Ersek wrote: > On 09/01/16 15:22, Marcel Apfelbaum wrote: > > +2.3 PCI only hierarchy > > +====================== > > +Legacy PCI devices can be plugged into pcie.0 as Integrated Devices or > > +into DMI-PCI bridge. PCI-PCI bridges can be plugged into DMI-PCI bridges > > +and can be nested until a depth of 6-7. DMI-BRIDGES should be plugged > > +only into pcie.0 bus. > > + > > + pcie.0 bus > > + ---------------------------------------------- > > + | | > > + ----------- ------------------ > > + | PCI Dev | | DMI-PCI BRIDGE | > > + ---------- ------------------ > > + | | > > + ----------- ------------------ > > + | PCI Dev | | PCI-PCI Bridge | > > + ----------- ------------------ > > + | | > > + ----------- ----------- > > + | PCI Dev | | PCI Dev | > > + ----------- ----------- > > Works for me, but I would again elaborate a little bit on keeping the > hierarchy flat. > > First, in order to preserve compatibility with libvirt's current > behavior, let's not plug a PCI device directly in to the DMI-PCI bridge, > even if that's possible otherwise. Let's just say > > - there should be at most one DMI-PCI bridge (if a legacy PCI hierarchy > is required), Why do you suggest this ? If the guest has multiple NUMA nodes and you're creating a PXB for each NUMA node, then it looks valid to want to have a DMI-PCI bridge attached to each PXB, so you can have legacy PCI devices on each NUMA node, instead of putting them all on the PCI bridge without NUMA affinity. > - only PCI-PCI bridges should be plugged into the DMI-PCI bridge, What's the rational for that, as opposed to plugging devices directly into the DMI-PCI bridge which seems to work ? Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|