From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 911622210D9CD for ; Mon, 26 Mar 2018 04:05:46 -0700 (PDT) Date: Mon, 26 Mar 2018 12:11:38 +0100 From: Jonathan Cameron Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory Message-ID: <20180326121138.00005e30@huawei.com> In-Reply-To: <24d8e5c2-065d-8bde-3f5d-7f158be9c578@deltatee.com> References: <20180312193525.2855-1-logang@deltatee.com> <20180312193525.2855-2-logang@deltatee.com> <59fd2f5d-177f-334a-a9c4-0f8a6ec7c303@codeaurora.org> <24d8e5c2-065d-8bde-3f5d-7f158be9c578@deltatee.com> MIME-Version: 1.0 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Logan Gunthorpe Cc: Jens Axboe , linux-block@vger.kernel.org, Alex Williamson , linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Sinan Kaya , =?ISO-8859-1?Q?J=E9r=F4me?= Glisse , Jason Gunthorpe , Benjamin Herrenschmidt , Bjorn Helgaas , Max Gurtovoy , Keith Busch , Eric Wehage , Christoph Hellwig List-ID: On Tue, 13 Mar 2018 10:43:55 -0600 Logan Gunthorpe wrote: > On 12/03/18 09:28 PM, Sinan Kaya wrote: > > On 3/12/2018 3:35 PM, Logan Gunthorpe wrote: > > Regarding the switch business, It is amazing how much trouble you went into > > limit this functionality into very specific hardware. > > > > I thought that we reached to an agreement that code would not impose > > any limits on what user wants. > > > > What happened to all the emails we exchanged? > > It turns out that root ports that support P2P are far less common than > anyone thought. So it will likely have to be a white list. This came as a bit of a surprise to our PCIe architect. His follow up was whether it was worth raising an ECR for the PCIe spec to add a capability bit to allow this to be discovered. This might long term avoid the need to maintain the white list for new devices. So is it worth having a long term solution for making this discoverable? Jonathan > Nobody else > seems keen on allowing the user to enable this on hardware that doesn't > work. The easiest solution is still limiting it to using a switch. From > there, if someone wants to start creating a white-list then that's > probably the way forward to support root ports. > > And there's also the ACS problem which means if you want to use P2P on > the root ports you'll have to disable ACS on the entire system. (Or > preferably, the IOMMU groups need to get more sophisticated to allow for > dynamic changes). > > Additionally, once you allow for root ports you may find the IOMMU > getting in the way. > > So there are great deal more issues to sort out if you don't restrict to > devices behind switches. > > Logan _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm