linux-kernel - Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory

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Date:   Wed, 14 Mar 2018 19:34:53 +0000
From:   "Stephen  Bates" <sbates@...thlin.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>
CC:     Bjorn Helgaas <helgaas@...nel.org>,
        Sinan Kaya <okaya@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "Christoph Hellwig" <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory

> P2P over PCI/PCI-X is quite common in devices like raid controllers.

Hi Dan 

Do you mean between PCIe devices below the RAID controller? Isn't it pretty novel to be able to support PCIe EPs below a RAID controller (as opposed to SCSI based devices)?

> It would be useful if those configurations were not left behind so
> that Linux could feasibly deploy offload code to a controller in the
> PCI domain.
   
Agreed. I think this would be great. Kind of like the XCOPY framework that was proposed a while back for SCSI devices [1] but updated to also include NVMe devices. That is definitely a use case we would like this framework to support.

Stephen
 
[1] https://lwn.net/Articles/592094/