From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D203C43613 for ; Mon, 24 Jun 2019 16:53:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EBA520673 for ; Mon, 24 Jun 2019 16:53:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732256AbfFXQxt (ORCPT ); Mon, 24 Jun 2019 12:53:49 -0400 Received: from ale.deltatee.com ([207.54.116.67]:37724 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728010AbfFXQxs (ORCPT ); Mon, 24 Jun 2019 12:53:48 -0400 Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.89) (envelope-from ) id 1hfSDs-0008FP-JW; Mon, 24 Jun 2019 10:53:41 -0600 To: Jason Gunthorpe , Christoph Hellwig Cc: Dan Williams , Linux Kernel Mailing List , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, linux-rdma , Jens Axboe , Bjorn Helgaas , Sagi Grimberg , Keith Busch , Stephen Bates References: <20190620161240.22738-1-logang@deltatee.com> <20190620193353.GF19891@ziepe.ca> <20190624073126.GB3954@lst.de> <20190624134641.GA8268@ziepe.ca> <20190624135024.GA11248@lst.de> <20190624135550.GB8268@ziepe.ca> From: Logan Gunthorpe Message-ID: <7210ba39-c923-79ca-57bb-7cf9afe21d54@deltatee.com> Date: Mon, 24 Jun 2019 10:53:38 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1 MIME-Version: 1.0 In-Reply-To: <20190624135550.GB8268@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: sbates@raithlin.com, kbusch@kernel.org, sagi@grimberg.me, bhelgaas@google.com, axboe@kernel.dk, linux-rdma@vger.kernel.org, linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, dan.j.williams@intel.com, hch@lst.de, jgg@ziepe.ca X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH 00/28] Removing struct page from P2PDMA X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 2019-06-24 7:55 a.m., Jason Gunthorpe wrote: > On Mon, Jun 24, 2019 at 03:50:24PM +0200, Christoph Hellwig wrote: >> On Mon, Jun 24, 2019 at 10:46:41AM -0300, Jason Gunthorpe wrote: >>> BTW, it is not just offset right? It is possible that the IOMMU can >>> generate unique dma_addr_t values for each device?? Simple offset is >>> just something we saw in certain embedded cases, IIRC. >> >> Yes, it could. If we are trying to do P2P between two devices on >> different root ports and with the IOMMU enabled we'll generate >> a new bus address for the BAR on the other side dynamically everytime >> we map. > > Even with the same root port if ACS is turned on could behave like this. Yup. > It is only a very narrow case where you can take shortcuts with > dma_addr_t, and I don't think shortcuts like are are appropriate for > the mainline kernel.. I don't think it's that narrow and it opens up a lot of avenues for system design that people are wanting to go. If your high speed data path can avoid the root complex and CPU, you can design a system which a much smaller CPU and fewer lanes directed at the CPU. Logan