Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751589AbdDNElH (ORCPT ); Fri, 14 Apr 2017 00:41:07 -0400 Received: from ale.deltatee.com ([207.54.116.67]:39232 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750734AbdDNElE (ORCPT ); Fri, 14 Apr 2017 00:41:04 -0400 To: Jason Gunthorpe , Bjorn Helgaas References: <1490911959-5146-1-git-send-email-logang@deltatee.com> <1491974532.7236.43.camel@kernel.crashing.org> <5ac22496-56ec-025d-f153-140001d2a7f9@deltatee.com> <1492034124.7236.77.camel@kernel.crashing.org> <81888a1e-eb0d-cbbc-dc66-0a09c32e4ea2@deltatee.com> <20170413232631.GB24910@bhelgaas-glaptop.roam.corp.google.com> <20170414041656.GA30694@obsidianresearch.com> Cc: Benjamin Herrenschmidt , Christoph Hellwig , Sagi Grimberg , "James E.J. Bottomley" , "Martin K. Petersen" , Jens Axboe , Steve Wise , Stephen Bates , Max Gurtovoy , Dan Williams , Keith Busch , linux-pci@vger.kernel.org, linux-scsi@vger.kernel.org, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm@ml01.01.org, linux-kernel@vger.kernel.org, Jerome Glisse From: Logan Gunthorpe Message-ID: <08c32f0d-6c7c-b65f-6453-dde0d7c173d1@deltatee.com> Date: Thu, 13 Apr 2017 22:40:46 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0 MIME-Version: 1.0 In-Reply-To: <20170414041656.GA30694@obsidianresearch.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 50.66.97.235 X-SA-Exim-Rcpt-To: jglisse@redhat.com, linux-kernel@vger.kernel.org, linux-nvdimm@ml01.01.org, linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, linux-pci@vger.kernel.org, keith.busch@intel.com, dan.j.williams@intel.com, maxg@mellanox.com, sbates@raithlin.com, swise@opengridcomputing.com, axboe@kernel.dk, martin.petersen@oracle.com, jejb@linux.vnet.ibm.com, sagi@grimberg.me, hch@lst.de, benh@kernel.crashing.org, helgaas@kernel.org, jgunthorpe@obsidianresearch.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory X-SA-Exim-Version: 4.2.1 (built Mon, 26 Dec 2011 16:24:06 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 750 Lines: 23 On 13/04/17 10:16 PM, Jason Gunthorpe wrote: > I'd suggest just detecting if there is any translation in bus > addresses anywhere and just hard disabling P2P on such systems. That's a fantastic suggestion. It simplifies things significantly. Unless there are any significant objections I think I will plan on doing that. > On modern hardware with 64 bit BARs there is very little reason to > have translation, so I think this is a legacy feature. Yes, p2pmem users are likely to be designing systems around it (ie JBOFs) and not trying to shoehorn it onto legacy architectures. At the very least, it makes sense to leave it out and if someone comes along who cares they can put in the effort to support the address translation. Thanks, Logan