linux-kernel - Re: [PATCH v2 10/10] nvmet: Optionally use PCI P2P memory

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Date:   Thu, 1 Mar 2018 23:32:46 +0000
From:   "Stephen  Bates" <sbates@...thlin.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     Logan Gunthorpe <logang@...tatee.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        "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>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Steve Wise <swise@...ngridcomputing.com>
Subject: Re: [PATCH v2 10/10] nvmet: Optionally use PCI P2P memory

>   No, locality matters. If you have a bunch of NICs and bunch of drives
>   and the allocator chooses to put all P2P memory on a single drive your
>   performance will suck horribly even if all the traffic is offloaded.
    
Sagi brought this up earlier in his comments about the _find_ function. We are planning to do something about this in the next version. This might be a randomization or a "user-pick" and include a rule around using the p2p_dev on the EP if that EP is part of the transaction.

Stephen