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

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Date:   Mon, 23 Oct 2017 16:04:26 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "'Petrosyan, Ludwig'" <ludwig.petrosyan@...y.de>
Cc:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "Linux-media@...r.kernel.org" <Linux-media@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Bridgman, John" <John.Bridgman@....com>,
        "Kuehling, Felix" <Felix.Kuehling@....com>,
        "Sagalovitch, Serguei" <Serguei.Sagalovitch@....com>,
        "Blinzer, Paul" <Paul.Blinzer@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "Sander, Ben" <ben.sander@....com>
Subject: Re: Enabling peer to peer device transactions for PCIe devices



On 23/10/17 10:08 AM, David Laight wrote:
> It is also worth checking that the hardware actually supports p2p transfers.
> Writes are more likely to be supported then reads.
> ISTR that some intel cpus support some p2p writes, but there could easily
> be errata against them.

Ludwig mentioned a PCIe switch. The few switches I'm aware of support 
P2P transfers. So if everything is setup correctly, the TLPs shouldn't 
even touch the CPU.

But, yes, generally it's a good idea to start with writes and see if 
they work first.

Logan