Commentary? What's the difference between a GPU and a vector processor? Is vector processors being open-source a desirable quality (compared to general attractiveness of open-source)?
Open hardware is less important than open software but that doesn't mean it isn't desirable. But anyway, vector v gpu:
Think AVX2 instead of GPU. You extend support for MIMD architecture will all the benefits of Out-of-Order execution and deep pipelines, but add data-level parallelism through SIMD or "vector" operations. This can allow significant performance gains for fundamentally sequential operation that still needs to perform linear algebra operation. Furthermore a lot of the speedup relies on unrolling sequential math operations and manually breaking data dependencies in the code, which has diminishing returns for larger vector/matrix dimensions (you'd spend more time loading/storing into GPU registers even if you had no bandwidth concerns over PCIe).
Vector processors/architectures are commonly found in special purpose architectures called Digital Signal Processors (DSPs), which are important for a variety of applications like automotive, aerospace, controls, audio, IoT, or anywhere with real-time data acquisition. FPGAs are also popular for this task.
However a lot of those devices are pretty cheap (or really expensive, not a lot of middle ground due to economies of scale) and either underclocked or overspec'd - meaning you either pay out the ass for an overkill processor or pay out the ass for a complicated systems architecture to use multiple chips on the same board (with proprietary tooling, shout-out to ADI)
Cheap(ish), low(ish) power, high(ish) clock, CPUs with 256 width vector operations are highly attractive in a number of markets. The fact that its open source makes it even more attractive, if you can afford to do a run of them.
> Under this model, each SM on an NIVIDA GPU corresponds to a more traditional CPU core. These SMs would contain some number of 32-wide vector registers. It seems that CUDA exposes operations on vector registers as a warp. They appear to be 32 threads because each instruction on 32 lanes at once, while the threads must proceed in lock step because they are actually a single stream of instructions.
>Is vector processors being open-source a desirable quality (compared to general attractiveness of open-source)?
Absolutely. Imagine an initiative to create a standardized open-source GPU for Linux? This vector processor could provide open source silicon IP to help build it.
This chip is just another step towards fully open-source systems.
In order to render current games / 3d with reasonable performance you need dedicated texturing hardware. Intel's Larrabee had it even though it never shipped as a graphics card. And early plans for the PS3 involved adding texture units to a Cell cpu, but Sony went with a Nvidia gpu instead.
A lot of later PS3 games started pulling GPU shading tasks onto the SPUs instead, because the shader pipeline was comparatively slow and SPUs were so well suited to the task. Here's a great presentation about occlusion on the SPE, part of a series of wonderful presentations about SPE use in Killzone 3: https://www.slideshare.net/guerrillagames/practical-occlusio...
Sampling/texturing helps but I can't help thinking that the software stack is the critical factor. You might make a great new open ecosystem but if I can't Port my OGL/OCL/etc benchmark to your hardware easily, I'm probably not going to waste my time.
Apparently this was the big thing that held Larrabee back as a GPU. The hardware was capable, but they never got their drivers to the point where they could do a good job with existing OpenGL, Direct3D, etc. code.
Is there any strong evidence of the claim that Larrabee HW had the potential of being a capable GPU, and that it was just a SW issue?
Despite being increasingly programmable, GPUs still have very fine-tuned hardware for graphics, and this goes deeper than just adding some texture mapping units here or there.
A good example of this is the fact that both Nvidia and AMD keep on adding new modes in HW to streamline graphics primitive processing with varying degrees of success (see mesh shaders and primitive shaders.)
To me, this signals that a free-for-all software approach as championed by Larrabee is simply not efficient enough in a competitive environment where GPUs are declared winner or loser based on benchmark differences of just a few percent.
Tom Forsyth's write up seems to make mostly reasonable claims. Though even he notes that it wasn't competitive with the high end at the time.
"So let's talk about the elephant in the room - graphics. Yes, at that we did fail. And we failed mainly for reasons of time and politics. And even then we didn't fail by nearly as much as people think. Because we were never allowed to ship it, people just saw a giant crater, but in fact Larrabee did run graphics, and it ran it surprisingly well. Larrabee emulated a fully DirectX11 and OpenGL4.x compliant graphics card - by which I mean it was a PCIe card, you plugged it into your machine, you plugged the monitor into the back, you installed the standard Windows driver, and... it was a graphics card. There was no other graphics cards in the system. It had the full DX11 feature set, and there were over 300 titles running perfectly - you download the game from Steam and they Just Work - they totally think it's a graphics card! But it's still actually running FreeBSD on that card, and under FreeBSD it's just running an x86 program called DirectXGfx (248 threads of it). And it shares a file system with the host and you can telnet into it and give it other work to do and steal cores from your own graphics system - it was mind-bending! And because it was software, it could evolve - Larrabee was the first fully DirectX11-compatible card Intel had, because unlike Gen we didn't have to make a new chip when Microsoft released a new spec. It was also the fastest graphics card Intel had - possibly still is. Of course that's a totally unfair comparison because Gen (the integrated Intel gfx processor) has far less power and area budget. But that should still tell you that Larrabee ran graphics at perfectly respectable speeds. I got very good at ~Dirt3 on Larrabee.
Of course, this was just the very first properly working chip (KNF had all sorts of problems, so KNC was the first shippable one) and the software was very young. No, it wasn't competitive with the fastest GPUs on the market at the time, unless you chose the workload very carefully (it was excellent at running Compute Shaders). If we'd had more time to tune the software, it would have got a lot closer. And the next rev of the chip would have closed the gap further. It would have been a very strong chip in the high-end visualization world, where tiny triangles, super-short lines and massive data sets are the main workloads - all things Larrabee was great at. But we never got the time or the political will to get there, and so the graphics side was very publicly cancelled."
On one hand, that statement supports my belief that there is more to graphics than just a lot of raw compute flops.
> It would have been a very strong chip in the high-end visualization world, where tiny triangles, super-short lines and massive data sets are the main workloads - all things Larrabee was great at.
But this goes the opposite way. :-)
Because you'd think that a lot of small primitives would make it harder to deploy those raw compute flops.
I think they mean something like SSE/AVX, but with something like ARM Scalable Vector Extension (code that works on registers with 128 to 2048 bit size, unknown at compile time).
