Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1951679AbdDYRDt (ORCPT ); Tue, 25 Apr 2017 13:03:49 -0400 Received: from ale.deltatee.com ([207.54.116.67]:49390 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1950846AbdDYRDk (ORCPT ); Tue, 25 Apr 2017 13:03:40 -0400 To: Knut Omang , Benjamin Herrenschmidt , Dan Williams References: <1490911959-5146-1-git-send-email-logang@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> <1492169849.25766.3.camel@kernel.crashing.org> <630c1c63-ff17-1116-e069-2b8f93e50fa2@deltatee.com> <20170414190452.GA15679@bhelgaas-glaptop.roam.corp.google.com> <1492207643.25766.18.camel@kernel.crashing.org> <1492311719.25766.37.camel@kernel.crashing.org> <5e43818e-8c6b-8be8-23ff-b798633d2a73@deltatee.com> <1492381907.25766.49.camel@kernel.crashing.org> <1493019397.3171.118.camel@oracle.com> <9b6c0830-a728-c7ca-e6c6-2135f3f760ed@deltatee.com> <1493101803.3171.246.camel@oracle.com> Cc: Bjorn Helgaas , Jason Gunthorpe , Christoph Hellwig , Sagi Grimberg , "James E.J. Bottomley" , "Martin K. Petersen" , Jens Axboe , Steve Wise , Stephen Bates , Max Gurtovoy , Keith Busch , linux-pci@vger.kernel.org, linux-scsi , linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm , "linux-kernel@vger.kernel.org" , Jerome Glisse From: Logan Gunthorpe Message-ID: <0cc95df5-b9dd-6493-15fe-771d535c1020@deltatee.com> Date: Tue, 25 Apr 2017 11:03:27 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <1493101803.3171.246.camel@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.111 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, 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, jgunthorpe@obsidianresearch.com, helgaas@kernel.org, dan.j.williams@intel.com, benh@kernel.crashing.org, knut.omang@oracle.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: 1222 Lines: 27 On 25/04/17 12:30 AM, Knut Omang wrote: > Yes, that's why I used 'significant'. One good thing is that given resources > it can easily be done in parallel with other development, and will give additional > insight of some form. Yup, well if someone wants to start working on an emulated RDMA device that actually simulates proper DMA transfers that would be great! >> I also imagine it would be quite difficult to develop those models >> given the array of hardware that needs to be supported and the deep >> functional knowledge required to figure out appropriate restrictions. > > From my naive perspective it seems it need not even be a full model to get some benefits, > just low level functionality tests with some instances of a > device that offers some MMIO space 'playground'. Yes, the nvme device in qemu has a CMB buffer which is a good choice to test with but we don't have code to use it for p2p transfers in the kernel so it is a bit awkward. We also posted [1] to qemu which was also handy to test with using a small out of tree module. But I don't see a lot of value in it if you completely ignore any hardware quirks. Logan [1] https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg04331.html