From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754000Ab1KVR1a (ORCPT ); Tue, 22 Nov 2011 12:27:30 -0500 Received: from palinux.external.hp.com ([192.25.206.14]:35428 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750898Ab1KVR12 (ORCPT ); Tue, 22 Nov 2011 12:27:28 -0500 Date: Tue, 22 Nov 2011 10:27:25 -0700 From: Matthew Wilcox To: Jean-Francois Dagenais Cc: "Michael S. Tsirkin" , "Hans J. Koch" , Greg KH , tglx@linutronix.de, linux-pci@vger.kernel.org, open list Subject: Re: extra large DMA buffer for PCI-E device under UIO Message-ID: <20111122172725.GK4387@parisc-linux.org> References: <20111118220849.GA25205@suse.de> <9E9C8A95-723C-427A-AD01-17284EDF7E4F@gmail.com> <20111121173620.GA5028@suse.de> <20111121181724.GB12011@local> <4498E0C9-B5E9-44B5-8868-140D6416100E@gmail.com> <20111122153525.GB17268@redhat.com> <40906F5E-5E97-44CF-AB95-40355204B63F@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40906F5E-5E97-44CF-AB95-40355204B63F@gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 22, 2011 at 11:54:22AM -0500, Jean-Francois Dagenais wrote: > That is quite interesting. It really seems like my VT-d recipe to create 128MB for my PCI-e > FPGA to write into is covered by this patch. > > My problem is that our FPGA is connected to one of the atom E6XX's PCI-e links, so no > iommu :( Since our first product had VT-d, the FPGA, uio based module and userspace > code is designed such that the device sees a huge contiguous memory chunk. This is key > to the performance of the FPGA, which is essentially decoupled from the CPU for it's real-time > acquisition. Is it really key? If you supported, ohidon'tknow, 2MB pages, you'd need 64 entries in the FPGA to store the addresses of those 2MB pages, which doesn't sound like a huge burden. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."