linux-kernel - Re: [PATCH v5 00/13] Copy Offload in NVMe Fabrics with P2P PCI Memory

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Date:   Thu, 30 Aug 2018 13:30:32 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        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>,
        Dan Williams <dan.j.williams@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v5 00/13] Copy Offload in NVMe Fabrics with P2P PCI Memory



On 30/08/18 01:20 PM, Jerome Glisse wrote:
> On Thu, Aug 30, 2018 at 12:53:39PM -0600, Logan Gunthorpe wrote:
> 
> [...]
> 
>>
>> When the PCI P2PDMA config option is selected the ACS bits in every
>> bridge port in the system are turned off to allow traffic to
>> pass freely behind the root port. At this time, the bit must be disabled
>> at boot so the IOMMU subsystem can correctly create the groups, though
>> this could be addressed in the future. There is no way to dynamically
>> disable the bit and alter the groups.

Oh, sorry this paragraph in the cover letter is wrong now. We now rely
on the disable_acs_redir command line option introduced in

aaca43fda742 ("PCI: Add "pci=disable_acs_redir=" parameter for
peer-to-peer support")


> Can you provide an example on how to test this ? Like kernel command
> line option, the doc patch does not have any such example. It would be
> nice to add.

Do you mean to test the patchset or the ACS bits you quoted?

Testing the patchset is a matter of having the right hardware (ie an
RDMA NIC and CMB enabled NVMe behind a PCIe switch, with the ACS bits
set correctly by the above command line option) and setting the p2pmem
configfs attribute in an nvme-of port to 'yes'.


Logan