linux-kernel - Re: [PATCH v3 00/14] Driver of Intel(R) Gaussian & Neural Accelerator

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Date:   Mon, 17 May 2021 22:10:25 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Daniel Stone <daniel@...ishbar.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Dave Airlie <airlied@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maciej Kwapulinski <maciej.kwapulinski@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v3 00/14] Driver of Intel(R) Gaussian & Neural Accelerator

Hi

Am 17.05.21 um 21:32 schrieb Daniel Stone:
> Hi,
> 
> On Mon, 17 May 2021 at 20:12, Thomas Zimmermann <tzimmermann@...e.de> wrote:
>> Am 17.05.21 um 09:40 schrieb Daniel Vetter:
>>> We have, it's called drivers/gpu. Feel free to rename to drivers/xpu or
>>> think G as in General, not Graphisc.
>>
>> I hope this was a joke.
>>
>> Just some thoughts:
>>
>> AFAICT AI first came as an application of GPUs, but has now
>> evolved/specialized into something of its own. I can imagine sharing
>> some code among the various subsystems, say GEM/TTM internals for memory
>> management. Besides that there's probably little that can be shared in
>> the userspace interfaces. A GPU is device that puts an image onto the
>> screen and an AI accelerator isn't.
> 
> But it isn't. A GPU is a device that has a kernel-arbitrated MMU
> hosting kernel-managed buffers, executes user-supplied compiled
> programs with reference to those buffers and other jobs, and informs
> the kernel about progress.
> 
> KMS lies under the same third-level directory, but even when GPU and
> display are on the same die, they're totally different IP blocks
> developed on different schedules which are just periodically glued
> together.

I mentioned this elsewhere: it's not about the chip architecture, it's 
about the UAPI. In the end, the GPU is about displaying things on a 
screen. Even if the rendering and the scanout engines are on different 
IP blocks. (Or different devices.)

The fact that one can do general purpose computing on a GPU is a 
byproduct of the evolution of graphics hardware. It never was the goal.


> 
>> Treating both as the same, even if
>> they share similar chip architectures, seems like a stretch. They might
>> evolve in different directions and fit less and less under the same
>> umbrella.
> 
> Why not? All we have in common in GPU land right now is MMU + buffer
> references + job scheduling + synchronisation. None of this has common
> top-level API, or even a common top-level model. It's not just ISA
> differences, but we have very old-school devices where the kernel
> needs to register fill on every job, living next to middle-age devices
> where the kernel and userspace co-operate to fill a ring buffer,
> living next to modern devices where userspace does some stuff and then
> the hardware makes it happen with the bare minimum of kernel
> awareness.

I see all this as an example why AI should not live under gpu/. There 
are already many generations of GPUs with different feature sets 
supported. Why lump more behind the same abstractions if AI can take a 
fresh start? Why should we care about AI and why should AI care about 
all our legacy.

We can still share all the internal code if AI needs any of it. 
Meanwhile AI drivers can provide their own UAPIs until a common 
framework emerges.

Again, just my 2 cents.

Best regards
Thomas

> 
> Honestly I think there's more difference between lima and amdgpu then
> there is between amdgpu and current NN/ML devices.
> 
> Cheers,
> Daniel
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer



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