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I want a good parallel computer

raphlinus.github.io

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Re: I want a good parallel computer

#111

Post by mattdesl »

Animats wrote: post #32

Interesting article. Other than as an exercise, it's not clear why someone would write a massively parallel 2D renderer that needs a GPU. Modern GPUs are overkill for 2D. Now, 3D renderers, we need all the help we can get. In this context, a "renderer" is something that takes in meshes, textures, materials, transforms, and objects, and generates images. It's not an entire game development engine, such as Unreal, Unit…

> Other than as an exercise, it's not clear why someone would write a massively parallel 2D renderer that needs a GPU. Modern GPUs are overkill for 2D. Now, 3D renderers, we need all the help we can get.

A ton of 2D applications could benefit from further GPU parallelization. Games, GUIs, blurs & effects, 2D animations, map apps, text and symbol rendering, data visualization...

Canvas2D in Chrome is already hardware accelerated, so most users get better performance and reduced load on main UI & CPU threads out of the box.

Re: I want a good parallel computer

#112

Post by zozbot234 »

dist-epoch wrote: post #15
turtletontine wrote: post #12

Earlier quoted context omitted.

Could you elaborate on this? How does many-small-CPUs make for a weirder programming model than a GPU? Im no expert, but I’ve done my fair share of parallel HPC stuff using MPI, and a little bit of Cuda. And to me the GPU programming model is far far “weirder” and harder to code for than the many-CPUs model. (Granted, I’m assuming you’re describing a different regime?)

In CUDA you don't really manage the individual compute units, you start a kernel, and the drivers take care of distributing that to the compute cores and managing the data flows between them. When programming CPUs however you are controlling and managing the individual threads. Of course, there are libraries which can do that for you, but fundamentally it's a different model.

The GPU equivalent of a single CPU "hardware thread" is called a "warp" or a "wavefront". GPU's can run many warps/wavefronts per compute unit by switching between warps to hide memory access latency. A CPU core can do this with two hardware threads, using Hyperthreading/2-way SMT, some CPU's have 4-way SMT, but GPU's push that quite a bit further.

Re: I want a good parallel computer

#113

Post by amelius »

Animats wrote: post #98
amelius wrote: post #51

Earlier quoted context omitted.

> Other than as an exercise, it's not clear why someone would write a massively parallel 2D renderer that needs a GPU. Modern GPUs are overkill for 2D. Depends on how complicated your artwork is.

There are only so many screen pixels.

You can have an unlimited number of polygons overlapping a pixel. For instance, if you zoom out a lot. Imagine you converted a layer map of a modern CPU design to svg, and tried to open it in Inkscape. Or a map of NYC. Wouldn't you think a bit of extra processing power would be welcomed?

Re: I want a good parallel computer

#114

Post by rjsw »

turtletontine wrote: post #35
grg0 wrote: post #19

The issue is that programming a discrete GPU feels like programming a printer over a COM port, just with higher bandwidths. It's an entirely moronic programming model to be using in 2025. - You need to compile shader source/bytecode at runtime; you can't just "run" a program. - On NUMA/discrete, the GPU cannot just manipulate the data structures the CPU already has; gotta copy the whole thing over. And you better des…

Your wish sounds to me a lot like Larrabee/Xeon Phi or manycore CPUs. Maybe I am misunderstanding something, but it sounds like a good idea to me and I don’t totally see why it inherently can’t compete with GPUs.

I think Intel should have made more of an effort to get cheap Larrabee boards to developers, they could have been ones with chips that had some broken cores or unable to make the design speed.

Re: I want a good parallel computer

#115

Post by amelius »

grg0 wrote: post #19

The issue is that programming a discrete GPU feels like programming a printer over a COM port, just with higher bandwidths. It's an entirely moronic programming model to be using in 2025. - You need to compile shader source/bytecode at runtime; you can't just "run" a program. - On NUMA/discrete, the GPU cannot just manipulate the data structures the CPU already has; gotta copy the whole thing over. And you better des…

> The issue is that programming a discrete GPU feels like programming a printer over a COM port, just with higher bandwidths.

To me it feels somewhat like programming for the segmented memory model with its near and far pointers, back in the old days. What a nightmare.

Re: I want a good parallel computer

#116

Post by snovymgodym »

CyberDildonics wrote: post #46
snovymgodym wrote: post #11

Earlier quoted context omitted.

Reminds me of Itanium

How is that at all like Itanium except for the superficial headline level where people say they are hard to program?

Because the main feature that made Itanium hard to program for was its explicit instruction-level parallelism.

Re: I want a good parallel computer

#117

Post by Brian_K_White »

deviantbit wrote: post #66
api wrote: post #56

Earlier quoted context omitted.

On flattening address spaces: the road not taken here is to run everything in something akin to the JVM, CLR, or WASM. Do that stuff in software not hardware. You could also do things like having the JIT optimize the entire running system dynamically like one program, eliminating syscall and context switch overhead not to mention most MMU overhead. Would it be faster? Maybe. The JIT would have to generate its own saf…

[flagged]

What the ever loving hell, it was a perfectly reasonable idea in response to another idea.

They weren't saying it should be done, and went out of the way to make it explicit that they are not claiming it would be better.

It was a thought exploration, and a valid one, even if it would not pan out if carried all the way to execution at scale. Yes it was handwaving. So what? All ideas start as mere thoughts, and it is useful, productive, and interesting to trade them back and forth in these things called conversations. Even "fantasy" and "handwavy" ones. Hell especially those. It's an early stage in the pollination and generation of new ideas that later become real engineering. Or not, either way the conversation and thought was entertaining. It's a thing humans do, in case you never met any or aren't one yourself.

The brainstorming was a hell of a lot more valid, interesting, and valuable than this shit. "Just go away" indeed.

Re: I want a good parallel computer

#118

Post by varelse »

deviantbit wrote: post #49

"I believe there are two main things holding it back." He really science’d the heck out of that one. I’m getting tired of seeing opinions dressed up as insight—especially when they’re this detached from how real systems actually work. I worked on the Cell processor and I can tell you it was a nightmare. It demanded an unrealistic amount of micromanagement and gave developers rope to hang themselves with. There’s a re…

[dead]

Re: I want a good parallel computer

#119

Post by tipsytoad »

Grosvenor wrote: post #30
grg0 wrote: post #19

The issue is that programming a discrete GPU feels like programming a printer over a COM port, just with higher bandwidths. It's an entirely moronic programming model to be using in 2025. - You need to compile shader source/bytecode at runtime; you can't just "run" a program. - On NUMA/discrete, the GPU cannot just manipulate the data structures the CPU already has; gotta copy the whole thing over. And you better des…

What I want is a Linear Algebra interface - As Gilbert Strang taught it. I'll "program" in LinAlg, and a JIT can compile it to whatever wonky way your HW requires. I'm not willing to even know about the HW at all, the higher level my code the more opportunities for the JIT to optimize my code. What I really want is something like Mathematica that can JIT to GPU. As another commenter mentioned all the API's assume you…

Like, PyTorch? And the new Mac minis have 512gb of unified memory

Re: I want a good parallel computer

#120

Post by CyberDildonics »

snovymgodym wrote: post #116
CyberDildonics wrote: post #46

Earlier quoted context omitted.

How is that at all like Itanium except for the superficial headline level where people say they are hard to program?

Because the main feature that made Itanium hard to program for was its explicit instruction-level parallelism.

They weren't talking about instruction level parallelism.
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