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

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Date:   Tue, 6 Jul 2021 11:56:17 -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 04:09:25PM +0200, Daniel Vetter wrote:
> Anyway, for anything that works like a gpu accelerator, like 3d accel,
> or parallel compute accel (aka gpgpu) or spatial compute accel (aka
> NN/AI) or maybe even fpga accel most of the magic to use the hardware
> is in this backend compiler, which translates from an IR into whatever
> your accelerator consumes. That's the part we really care about for
> modern accelerators because without that defacto the hardware is
> useless. Generally these chips have full-blown, if special purpose
> ISA, with register files, spilling, branches, loops and other control
> flow (sometimes only execution masks on simpler hw).

I don't know if I see it so clearly as you do - at the end of the day
the user keys in the program in some proprietary (or open!) language
and and wack of propritary magic transforms it to "make it work".

There are many barriers that prevent someone without the secret
knowledge from duplicating the end result of a working program. An
accelerator ISA is certainly one example, but I wouldn't overly focus
on it as the only blocker.

Like you said below the NVIDIA GPU ISA seems known but the HW is still
not really useful for other reasons.

Habana seems to have gone the other way, the HW is fully useful but we
don't have the ISA transformation and other details.

Both cases seem to have ended up with something useless, and I have a
hard time saying nouveau has more right to be in the kernel tree than
Habana does.

> > Honestly, I think GPU is approaching this backwards. Wayland should
> > have been designed to prevent proprietary userspace stacks.
> 
> That's not possible without some serious cans of worms though. Wayland
> is a protocol, and you can't forbid people from implementing it.
> Otherwise all the compatible open implementations of closed protocols
> wouldn't be possible either.

Well, in many ways so is Linux, but nobody would seriously
re-implement Linux just to produce a driver.

> So I'm not clear what you're suggesting here we should do different.

Not enabling proprietary stacks as above would be a good start.

Jason