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

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Message-ID: <CAPcyv4gw0rsMNvG=xMRFV0=4MkGuXis5L17Jm3fU69EZAVAS4A@mail.gmail.com>
Date:   Tue, 6 Dec 2016 14:02:19 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Stephen Bates <sbates@...thlin.com>,
        Haggai Eran <haggaie@...lanox.com>,
        "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>,
        "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 Tue, Dec 6, 2016 at 1:47 PM, Logan Gunthorpe <logang@...tatee.com> wrote:
> Hey,
>
>> Okay, so clearly this needs a kernel side NVMe specific allocator
>> and locking so users don't step on each other..
>
> Yup, ideally. That's why device dax isn't ideal for this application: it
> doesn't provide any way to prevent users from stepping on each other.

On this particular point I'm in the process of posting patches that
allow device-dax sub-division, so you could carve up a bar into
multiple devices of various sizes.