Re: Enabling peer to peer device transactions for PCIe devices

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: Enabling peer to peer device transactions for PCIe devices
Date	2016-12-05 19:50 +0100
Message-ID	<sL6uR-8aT-1@gated-at.bofh.it> (permalink)
References	(8 earlier) <sL55L-7o6-29@gated-at.bofh.it> <sL5yN-7xB-5@gated-at.bofh.it> <sL5Sa-7U6-7@gated-at.bofh.it> <sL5Sa-7U6-5@gated-at.bofh.it> <sL6lc-87B-29@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Dec 5, 2016 at 10:39 AM, Logan Gunthorpe <logang@deltatee.com> wrote:
> On 05/12/16 11:08 AM, Dan Williams wrote:
>>
>> I've already recommended that iopmem not be a block device and instead
>> be a device-dax instance. I also don't think it should claim the PCI
>> ID, rather the driver that wants to map one of its bars this way can
>> register the memory region with the device-dax core.
>>
>> I'm not sure there are enough device drivers that want to do this to
>> have it be a generic /sys/.../resource_dmableX capability. It still
>> seems to be an exotic one-off type of configuration.
>
>
> Yes, this is essentially my thinking. Except I think the userspace interface
> should really depend on the device itself. Device dax is a good  choice for
> many and I agree the block device approach wouldn't be ideal.
>
> Specifically for NVME CMB: I think it would make a lot of sense to just hand
> out these mappings with an mmap call on /dev/nvmeX. I expect CMB buffers
> would be volatile and thus you wouldn't need to keep track of where in the
> BAR the region came from. Thus, the mmap call would just be an allocator
> from BAR memory. If device-dax were used, userspace would need to lookup
> which device-dax instance corresponds to which nvme drive.
>

I'm not opposed to mapping /dev/nvmeX.  However, the lookup is trivial
to accomplish in sysfs through /sys/dev/char to find the sysfs path of
the device-dax instance under the nvme device, or if you already have
the nvme sysfs path the dax instance(s) will appear under the "dax"
sub-directory.

Thread

Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-11-25 20:40 +0100
  Re: Enabling peer to peer device transactions for PCIe devices Christian König <deathsimple@vodafone.de> - 2016-11-25 21:50 +0100
    Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-11-25 22:20 +0100
  Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-11-28 18:00 +0100
    Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-11-28 19:30 +0100
      Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-11-28 22:40 +0100
        Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-11-28 23:30 +0100
    Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-11-28 20:10 +0100
      Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-11-30 17:30 +0100
        Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-11-30 19:10 +0100
          Re: Enabling peer to peer device transactions for PCIe devices "Stephen Bates" <sbates@raithlin.com> - 2016-12-04 14:10 +0100
          Re: Enabling peer to peer device transactions for PCIe devices "Stephen Bates" <sbates@raithlin.com> - 2016-12-04 14:50 +0100
            Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-12-05 18:20 +0100
              Re: Enabling peer to peer device transactions for PCIe devices Dan Williams <dan.j.williams@intel.com> - 2016-12-05 18:50 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Dan Williams <dan.j.williams@intel.com> - 2016-12-05 19:10 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-12-05 19:40 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Dan Williams <dan.j.williams@intel.com> - 2016-12-05 19:50 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-12-05 20:20 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-12-05 20:30 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-12-05 20:50 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-12-05 21:00 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Christoph Hellwig <hch@infradead.org> - 2016-12-05 21:10 +0100
                Re: Enabling peer to peer device transactions for PCIe devices "Stephen Bates" <sbates@raithlin.com> - 2016-12-06 09:30 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-12-06 17:40 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-12-06 18:00 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-12-06 18:30 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Logan Gunthorpe <logang@deltatee.com> - 2016-12-06 22:50 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Dan Williams <dan.j.williams@intel.com> - 2016-12-06 23:10 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Christoph Hellwig <hch@infradead.org> - 2016-12-06 18:20 +0100
                Re: Enabling peer to peer device transactions for PCIe devices Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-12-05 19:10 +0100
      RE: Enabling peer to peer device transactions for PCIe devices "Deucher, Alexander" <Alexander.Deucher@amd.com> - 2016-11-30 18:50 +0100
    Re: Enabling peer to peer device transactions for PCIe devices Haggai Eran <haggaie@mellanox.com> - 2016-11-28 21:00 +0100
  Re: Enabling peer to peer device transactions for PCIe devices Haggai Eran <haggaie@mellanox.com> - 2016-11-28 19:40 +0100

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