From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752168AbeCZQls (ORCPT ); Mon, 26 Mar 2018 12:41:48 -0400 Received: from mail-db5eur01on0053.outbound.protection.outlook.com ([104.47.2.53]:3296 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751489AbeCZQlp (ORCPT ); Mon, 26 Mar 2018 12:41:45 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=jgg@mellanox.com; Date: Mon, 26 Mar 2018 10:41:29 -0600 From: Jason Gunthorpe To: Jonathan Cameron Cc: Logan Gunthorpe , Sinan Kaya , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, Stephen Bates , Christoph Hellwig , Jens Axboe , Keith Busch , Sagi Grimberg , Bjorn Helgaas , Max Gurtovoy , Dan Williams , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Benjamin Herrenschmidt , Alex Williamson , Eric Wehage Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory Message-ID: <20180326164129.GF15530@mellanox.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> <20180326121138.00005e30@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; 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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. I know Mellanox and Nvidia have been doing p2p on Intel root complexes for something like 5-6 years now.. I don't have the details, but it does seem to work. I have heard some chips give poor performance.. Also AMD GPU SLI uses P2P these days, so this isn't exactly a niche feature in Intel/AMD land. I think the main issue here is that there is some BIOS involvement to set things up properly. Eg in GPU land motherboards certify for 'crossfire' support. > 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. If it is primarily a BIOS issue then it should be an ACPI thing, right? Jason