Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

From	Logan Gunthorpe <logang@deltatee.com>
Newsgroups	linux.kernel
Subject	Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
Date	2017-04-19 00:20 +0200
Message-ID	<txJDz-3bW-1@gated-at.bofh.it> (permalink)
References	(6 earlier) <txHiq-1Gh-21@gated-at.bofh.it> <txIxP-2AU-17@gated-at.bofh.it> <txIHv-2Es-1@gated-at.bofh.it> <txIRb-2HH-5@gated-at.bofh.it> <txJ0S-2KJ-13@gated-at.bofh.it>
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On 18/04/17 03:36 PM, Dan Williams wrote:
> On Tue, Apr 18, 2017 at 2:22 PM, Jason Gunthorpe
> <jgunthorpe@obsidianresearch.com> wrote:
>> On Tue, Apr 18, 2017 at 02:11:33PM -0700, Dan Williams wrote:
>>>> I think this opens an even bigger can of worms..
>>>
>>> No, I don't think it does. You'd only shim when the target page is
>>> backed by a device, not host memory, and you can figure this out by a
>>> is_zone_device_page()-style lookup.
>>
>> The bigger can of worms is how do you meaningfully stack dma_ops.
> 
> This goes back to my original comment to make this capability a
> function of the pci bridge itself. The kernel has an implementation of
> a dynamically created bridge device that injects its own dma_ops for
> the devices behind the bridge. See vmd_setup_dma_ops() in
> drivers/pci/host/vmd.c.

Well the issue I think Jason is pointing out is that the ops don't
stack. The map_* function in the injected dma_ops needs to be able to
call the original map_* for any page that is not p2p memory. This is
especially annoying in the map_sg function which may need to call a
different op based on the contents of the sgl. (And please correct me if
I'm not seeing how this can be done in the vmd example.)

Also, what happens if p2p pages end up getting passed to a device that
doesn't have the injected dma_ops?

However, the concept of replacing the dma_ops for all devices behind a
supporting bridge is interesting and may be a good piece of the final
solution.

Logan

Thread

Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-16 17:50 +0200
  Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-16 18:50 +0200
    Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-17 00:40 +0200
      Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-17 07:20 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-17 09:30 +0200
          Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-17 19:00 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-17 19:10 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 07:30 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jerome Glisse <jglisse@redhat.com> - 2017-04-17 20:10 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 08:20 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-17 23:20 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 07:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-18 08:40 +0200
  Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-17 00:30 +0200
    Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-18 18:50 +0200
      Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-18 19:30 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-18 20:10 +0200
          Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-18 20:40 +0200
          Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 03:20 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 01:00 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 02:10 +0200
      Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 20:40 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-18 21:10 +0200
          Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 21:40 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-18 21:50 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 22:10 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-18 21:50 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jerome Glisse <jglisse@redhat.com> - 2017-04-18 22:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-18 22:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 22:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 03:20 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-18 23:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-18 23:20 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-18 23:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-18 23:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 00:20 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 00:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 00:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 01:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 01:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 03:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 00:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 01:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 01:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 01:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 03:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-18 23:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 00:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 01:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 04:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-19 03:30 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 18:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 18:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 19:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jerome Glisse <jglisse@redhat.com> - 2017-04-19 19:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 19:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 20:20 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 20:20 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 20:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-19 20:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 20:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-20 22:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory "Stephen  Bates" <sbates@raithlin.com> - 2017-04-21 01:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-21 07:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory "Stephen  Bates" <sbates@raithlin.com> - 2017-04-20 22:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 19:20 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 20:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 20:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 21:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 21:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-19 21:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-19 22:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-20 01:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@gmail.com> - 2017-04-20 02:10 +0200

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