From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ale.deltatee.com (ale.deltatee.com [207.54.116.67]) (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 A4A1C21F85E61 for ; Mon, 26 Mar 2018 10:24:33 -0700 (PDT) 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> <20180326121138.00005e30@huawei.com> <20180326164129.GF15530@mellanox.com> From: Logan Gunthorpe Message-ID: <6ead7f19-c0e5-5584-2518-1e1889a007e4@deltatee.com> Date: Mon, 26 Mar 2018 11:30:38 -0600 MIME-Version: 1.0 In-Reply-To: <20180326164129.GF15530@mellanox.com> Content-Language: en-US Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory 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: Jason Gunthorpe , Jonathan Cameron 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 , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Benjamin Herrenschmidt , Bjorn Helgaas , Max Gurtovoy , Keith Busch , Eric Wehage , Christoph Hellwig List-ID: On 26/03/18 10:41 AM, Jason Gunthorpe wrote: > On Mon, Mar 26, 2018 at 12:11:38PM +0100, Jonathan Cameron wrote: >> 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. > > I don't think it is a hardware problem. The latest and greatest Power9 CPUs still explicitly do not support this. And, if I recall correctly, the ARM64 device we played with did not either -- but I suspect that will differ depending on vendor. The latest Intel devices of course do support it, but go back 3-4 years or so and the performance is pretty much unusable (at least for the purposes of what this patchset implements). Even older CPUs did not support it. We haven't done any testing on AMD devices but I assume they are similar to Intel. In any case, even if every CPU manufactured today supported it well, there are still older devices out there without support that we need to ensure are handled properly. Logan _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm