
Intel Xe-LP GPU Architecture Deep Dive - m3at
https://www.anandtech.com/show/15973/the-intel-xelp-gpu-architecture-deep-dive-building-up-from-the-bottom
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pjmlp
> The downside is that it also means that Intel is the only hardware vendor
> launching a new GPU/architecture in 2020 without support for the next
> generation of features, which Microsoft & co are codifying as DirectX 12
> Ultimate. The consumer-facing trade name for feature level 12_2, DirectX
> Ultimate incorporates support for variable rate shading tier 2, along with
> ray tracing, mesh shaders, and sampler feedback. And to be fair to Intel,
> expecting ray tracing in an integrated part in 2020 was always a bit too
> much of an ask. But some additional progress would always be nice to see.
> Plus it puts DG1 in a bit of an odd spot, since it’s a discrete GPU without
> 12_2 functionality.

Not really on a good starting foot.

~~~
gigatexal
meh. Ray tracing is hype. I don't think it's omission is that big of a deal.

~~~
pjmlp
Hollywood is of a different point of view.

[https://home.otoy.com/](https://home.otoy.com/)

[https://www.disneyanimation.com/technology/innovations/hyper...](https://www.disneyanimation.com/technology/innovations/hyperion)

Also a standard feature of PS 5 and XBox Series X.

~~~
gigatexal
The price premiums for hardware with ray tracing hardware is still high and
only when it becomes common place so as to not command a higher price will
your average gamer care. There’s also always the next gen for Intel to add it.

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dragontamer
CPU cores are pretty much a done deal IMO (unless Nuvia's hype is real. I
guess we'll see about that soon). For the last 10, maybe 20 years, CPUs have
simply grown bigger and have more or less done the same features.

CPUs simply push wider SIMD (SSE -> AVX -> AVX512), bigger out-of-execution
buffers, larger registers, deeper branch prediction, more cache. The biggest
advancement seemed to be Intel's uop-cache in Sandy Bridge (a concept that was
first tried in the Pentium4, so not really a "new" innovation).

Even ARM chips are more of the same. Wider SIMD (see A64fx: #1 supercomputer
in the world for 512-bit SVE), deeper out-of-order execution, better branch
prediction. Its rare to see something new

\----------

In contrast, whenever I see GPU-architectures, everything is so hugely
different. True, GPUs all have a "SIMD focus", but there's so many exciting
things about SIMD that just haven't been explored yet.

NVidia has Tensor-cores, Raytracing cores. It was already crazy that NVidia
had a full matrix-multiplication implemented in its FP16 processor in Volta,
but Ampere is now pushing sparse matrix multiplication at the chip level (!!).

AMD GCN and RDNA push GPU/SIMD architecture in a different direction. While a
chunk of RDNA can be described as "more of the same", the "SubVector
execution" feature grossly changes how Wave64 wavefronts are executed to save
on register space and potentially have a better memory access pattern.
Innovation continues in the AMD space for sure.

Intel finally enters with their GPU / SIMD architecture, and they start of
with... SIMD8 + SIMD2 (instead of the Wave32 of RDNA/NVidia or Wave64 for
GCN). Finally, Intel is minimizing hardware scheduling (saving on die area),
and focusing on software to schedule the instructions.

Three very, very different architectures. Three very different ideologies for
how SIMD compute / GPUs should be built. The SIMD / GPU architecture space
remains more innovative than the CPU-architecture space by a longshot. Its
exciting to see.

\--------

I'm not saying that CPU-advancements are dead per se. AMD did make chiplets a
hot commodity (but chiplets were already experimented with Power5, and
chiplets seem like a natural evolution to dual-socket or NUMA architectures...
just cheap enough for a consumer now). Intel's new Tremont Atom core has this
cool "dual-decoder" design (where one decoder works on one-branch, and the 2nd
decoder works on a 2nd branch in parallel). There are certainly new ideas
being tested in the CPU world. But nothing as majorly game changing as what
Intel / AMD / NVidia are doing to the GPU space. (Or Google if we include TPUs
in the discussion. A TPU isn't SIMD, but it shares some degree of similarity,
especially to NVidia's Tensor cores)

I guess big.LITTLE (and Intel's Lakefield platform) was a big change in the
last 10 years. But that hasn't really seen much success in the Desktop/Server
markets.

~~~
awalton
David Kanter makes an excellent point about why CPUs still aren't going away
any time soon - nobody's building GPUs with arbitrarily upgradeable memory,
and there are still more larger-than-memory problems you want these systems to
be able to tackle. As soon as your data set is too big for memory, you're
basically forced to head to a CPU to coordinate things. And as big as some GPU
memories have grown, the ML programming models are vastly bigger still, so
there's still a lot of reasons you want a CPU in these systems.

So naturally the market is currently trying to find a middle, which is exactly
where Intel's been heading if you've been paying any attention. That's the
total explanation on why CPUs have been getting wider and wider - it just
makes sense for them to, given the transistor budgets and the fact that just
stamping more CPUs on a core is already showing signs of diminishing returns
(to the point where you _have_ to use an approach like chiplets to manage
thermals appropriately, even).

The laptop market being repressed by Microsoft's stone-aged kernel CPU core
management holding back designs like Lakefield (which are now completely old
hat for phone-class processors) for a decade is a completely different
discussion and really goes out of band with what we're talking about here
though.

~~~
dragontamer
To clarify: I don't mean to say that GPUs will become superior to CPUs.

Just that CPUs are a mature technology that seem unlikely to have any dramatic
evolution any time soon. GPUs in contrast, are a lesser understood
architecture with significant amounts of experimentation still being done on
them. Its a more exciting field to keep an eye on.

After all, CPUs are latency optimized, GPUs are bandwidth optimized. They're
made for different kinds of problems.

