From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hawkins Subject: Re: [RFC v2] virtio: add virtio-over-PCI driver Date: Tue, 14 Apr 2009 15:27:16 -0700 Message-ID: <49E50DC4.3080108@ovro.caltech.edu> References: <20090224000002.GA578@ovro.caltech.edu> <49E4FED0.1020003@ovro.caltech.edu> <49E505B3.5070005@ovro.caltech.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ira Snyder , Arnd Bergmann , Jan-Bernd Themann , netdev@vger.kernel.org, Rusty Russell , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org To: Grant Likely Return-path: Received: from ovro.ovro.caltech.edu ([192.100.16.2]:37289 "EHLO ovro.ovro.caltech.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753762AbZDNW1P (ORCPT ); Tue, 14 Apr 2009 18:27:15 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: Hi Grant, > Hmmm, I hadn't thought about this. I was intending to use the > Virtex's memory region for all virtio, but if I can allocate memory > regions on both sides of the PCI bus, then that may be best. Sounds like you can experiment and see what works best :) >> If you use >> a PCI Target only core, then the MPC5200 DMA controller >> will have to do all the work, and read transfers might >> be slightly less efficient. > > I'll definitely intend to enable master mode on the Xilinx PCI controller. Since you understand the lingo, you clearly understand there are core differences :) >> Our target boards (PowerPC) live in compactPCI backplanes >> and talk to x86 boards that do not have DMA controllers. >> So the PCI target board DMA controllers are used to >> transfer data efficiently to the x86 host (writes) >> and less efficiently from the host to the boards >> (reads). Our bandwidth requirements are 'to the host', >> so we can live with the asymmetry in performance. > > Fortunately I don't have very high bandwidth requirements for the > first spin, so I have some room to experiment. :-) Yes, in theory you have enough bandwidth ... then a few features are added, the PCI core is not quite as fast as advertised, etc etc :) Cheers, Dave