linux-kernel - Re: Enabling peer to peer device transactions for PCIe devices

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Message-ID: <c1ead8a0-6850-fc84-2793-b986f5c1f726@mellanox.com>
Date:   Sun, 4 Dec 2016 09:42:22 +0200
From:   Haggai Eran <haggaie@...lanox.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "Suravee.Suthikulpanit@....com" <Suravee.Suthikulpanit@....com>,
        "John.Bridgman@....com" <John.Bridgman@....com>,
        "Alexander.Deucher@....com" <Alexander.Deucher@....com>,
        "Linux-media@...r.kernel.org" <Linux-media@...r.kernel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Max Gurtovoy <maxg@...lanox.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "serguei.sagalovitch@....com" <serguei.sagalovitch@....com>,
        "Paul.Blinzer@....com" <Paul.Blinzer@....com>,
        "Felix.Kuehling@....com" <Felix.Kuehling@....com>,
        "ben.sander@....com" <ben.sander@....com>
Subject: Re: Enabling peer to peer device transactions for PCIe devices

On 11/30/2016 8:01 PM, Logan Gunthorpe wrote:
> 
> 
> On 30/11/16 09:23 AM, Jason Gunthorpe wrote:
>>> Two cases I can think of are RDMA access to an NVMe device's controller
>>> memory buffer,
>>
>> I'm not sure on the use model there..
> 
> The NVMe fabrics stuff could probably make use of this. It's an
> in-kernel system to allow remote access to an NVMe device over RDMA. So
> they ought to be able to optimize their transfers by DMAing directly to
> the NVMe's CMB -- no userspace interface would be required but there
> would need some kernel infrastructure.

Yes, that's what I was thinking. The NVMe/f driver needs to map the CMB for
RDMA. I guess if it used ZONE_DEVICE like in the iopmem patches it would be
relatively easy to do.