linux-kernel - Re: [PATCH v4 0/2] Add p2p via dmabuf to habanalabs

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Date:   Tue, 6 Jul 2021 14:28:28 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Oded Gabbay <oded.gabbay@...il.com>,
        Oded Gabbay <ogabbay@...nel.org>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Gal Pressman <galpress@...zon.com>, sleybo@...zon.com,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Doug Ledford <dledford@...hat.com>,
        Dave Airlie <airlied@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        Leon Romanovsky <leonro@...dia.com>,
        Christoph Hellwig <hch@....de>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v4 0/2] Add p2p via dmabuf to habanalabs

On Tue, Jul 06, 2021 at 06:07:17PM +0200, Daniel Vetter wrote:

> Also on your claim that drivers/gpu is a non-upstream disaster: I've
> also learned that that for drivers/rdma there's the upstream driver,
> and then there's the out-of-tree hackjob the vendor actually
> supports.

In the enterprise world everyone has their out of tree backport
drivers. It varies on the vendor how much deviation there is from the
upstream driver and what commercial support relationship the vendor
has with the enterprise distros.

> So seems to be about the same level of screwed up, if you ask the
> vendor they tell you the upstream driver isn't a thing they care about
> and it's just done for a bit of goodwill. 

Sounds like you should get a new RDMA supplier :)

To be fair Intel is getting better, they got their new RDMA HW support
merged into v5.14 after about 2 years in the out of tree world. Though
it is still incomplete compared to their out of tree driver, the gap
is much smaller now.

> amounts of volume, then suddenly it's an option ... Minus the fw issue
> for nvidia, upstream does support all the gpus you can buy right now
> and that can run on linux with some vendor driver (aka excluding apple
> M1 and ofc upcoming products from most vendors).

I would look at how many actual commercial systems are running the
upstream/inbox stack. I personally know of quite a few sites with big
HPC RDMA deployments running pure inbox kernels, no add on kernel
modules, with full commercial support.

If you can say that kind of arrangment is also common place in the GPU
world then I will happily be wrong.

Jason