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

From Benjamin Herrenschmidt <benh@au1.ibm.com>
Newsgroups linux.kernel
Subject Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
Date 2017-04-14 13:50 +0200
Message-ID <tw7TI-Aq-9@gated-at.bofh.it> (permalink)
References (4 earlier) <tvUts-jx-17@gated-at.bofh.it> <tvWlz-1Bt-7@gated-at.bofh.it> <tw0Se-4NC-9@gated-at.bofh.it> <tw1lf-528-5@gated-at.bofh.it> <tw7TI-Aq-11@gated-at.bofh.it>
Organization IBM Australia

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On Fri, 2017-04-14 at 21:37 +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2017-04-13 at 22:40 -0600, Logan Gunthorpe wrote:
> > 
> > On 13/04/17 10:16 PM, Jason Gunthorpe wrote:
> > > I'd suggest just detecting if there is any translation in bus
> > > addresses anywhere and just hard disabling P2P on such systems.
> > 
> > That's a fantastic suggestion. It simplifies things significantly.
> > Unless there are any significant objections I think I will plan on
> > doing
> > that.
> 
> I object.

Note: It would also make your stuff fundamentally incompatible with
KVM guest pass-through since KVM plays with remapping BARs all over
the place.

Ben.

> > > On modern hardware with 64 bit BARs there is very little reason
> > > to
> > > have translation, so I think this is a legacy feature.
> > 
> > Yes, p2pmem users are likely to be designing systems around it (ie
> > JBOFs) and not trying to shoehorn it onto legacy architectures.
> > 
> > At the very least, it makes sense to leave it out and if someone
> > comes
> > along who cares they can put in the effort to support the address
> > translation.
> > 
> > Thanks,
> > 
> > Logan

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Thread

Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-12 08:30 +0200
  Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-12 19:20 +0200
    Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-13 00:00 +0200
      Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-13 23:30 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-14 00:40 +0200
        Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Bjorn Helgaas <helgaas@kernel.org> - 2017-04-14 01:30 +0200
          Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2017-04-14 06:20 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-14 06:50 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@au1.ibm.com> - 2017-04-14 13:50 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-14 15:00 +0200
            Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-14 13:40 +0200
              Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-14 19:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Bjorn Helgaas <helgaas@kernel.org> - 2017-04-14 21:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-15 00:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-15 19:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-16 00:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-16 05:10 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-16 06:50 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams <dan.j.williams@intel.com> - 2017-04-16 18:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-16 18:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-17 01:00 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Knut Omang <knut.omang@oracle.com> - 2017-04-24 09:40 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-24 18:20 +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 Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-04-16 00:20 +0200
                Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe <logang@deltatee.com> - 2017-04-16 07:40 +0200

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