From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54335) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bhWFD-0001f5-Uj for qemu-devel@nongnu.org; Wed, 07 Sep 2016 02:22:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bhWF7-0004Nw-Pt for qemu-devel@nongnu.org; Wed, 07 Sep 2016 02:21:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53300) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bhWF7-0004Nn-KC for qemu-devel@nongnu.org; Wed, 07 Sep 2016 02:21:53 -0400 Message-ID: <1473229310.28663.14.camel@redhat.com> From: Gerd Hoffmann Date: Wed, 07 Sep 2016 08:21:50 +0200 In-Reply-To: <739af9d6-2382-c4bd-679d-87b153124491@redhat.com> References: <1472736127-18137-1-git-send-email-marcel@redhat.com> <6c9103e7-70ad-55c6-5533-d6d9bbaa39b4@redhat.com> <739af9d6-2382-c4bd-679d-87b153124491@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 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, mst@redhat.com, Peter Maydell , Drew Jones , Laine Stump , Andrea Bolognani , Alex Williamson Hi, > >> ports, if that's allowed). For example: > >> > >> - 1-32 ports needed: use root ports only > >> > >> - 33-64 ports needed: use 31 root ports, and one switch with 2-32 > >> downstream ports I expect you rarely need any switches. You can go multifunction with the pcie root ports. Which is how physical q35 works too btw, typically the root ports are on slot 1c for intel chipsets: nilsson root ~# lspci -s1c 00:1c.0 PCI bridge: Intel Corporation 7 Series/C210 Series Chipset Family PCI Express Root Port 1 (rev c4) 00:1c.1 PCI bridge: Intel Corporation 7 Series/C210 Series Chipset Family PCI Express Root Port 2 (rev c4) 00:1c.2 PCI bridge: Intel Corporation 7 Series/C210 Series Chipset Family PCI Express Root Port 3 (rev c4) Root bus has 32 slots, a few are taken (host bridge @ 00.0, lpc+sata @ 1f.*, pci bridge @ 1e.0, maybe vga @ 01.0), leaving 28 free slots. With 8 functions each you can have up to 224 root ports without any switches, and you have not many pci bus numbers left until you hit the 256 busses limit ... cheers, Gerd