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I want a good parallel computer

raphlinus.github.io

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Re: I want a good parallel computer

#161

Post by jms55 »

raphlinus wrote: post #103
dragontamer wrote: post #95

There's a lot here that seems to misunderstand GPUs and SIMD. Note that raytracing is a very dynamic problem, where the GPU isn't sure if a ray hits a geometry or if it misses. When it hits, the ray needs to bounce, possibly multiple times. Various implementations of raytracing, recursion, dynamic parallelism or whatever. Its all there. Now the software / compilers aren't ready (outside of specialized situations like…

The problems I'm having are very different than those for raytracing. Sure, it's dynamic, but at a fine granularity, so the problems you run into are divergence, and often also wanting function pointers, which don't work well in a SIMT model, By contrast, the way I'm doing 2D there's basically no divergence (monoids are cool that way) but there is a need to schedule dynamically at a coarser (workgroup) level. But the…

> But the biggest problem I'm having is management of buffer space for intermediate objects

My advice for right now (barring new APIs), if you can get away with it, is to pre-allocate a large scratch buffer for as big of a workload as you will have over the program's life, and then have shaders virtually sub-allocate space within that buffer.

Re: I want a good parallel computer

#162

Post by __d »

deviantbit wrote: post #38
IshKebab wrote: post #3

Having worked for a company that made a "hundreds of small CPUs on a single chip", I can tell you now that they're all going to fail because the programming model is too weird, and nobody will write software for them. Whatever comes next will be a GPU with extra capabilities, not a totally new architecture. Probably an nVidia GPU.

Yep, transputers failed miserably. I wrote a ton a code for them. Everything had to be solved in a serial bus, which defeated the purpose of the transputer.

Could you elaborate on the “serial bus” bit?

Re: I want a good parallel computer

#163

Post by __d »

deviantbit wrote: post #74
morphle wrote: post #63

Earlier quoted context omitted.

I shipped 5 applications on an 800 Inmos Transputer supercomputer. Sold my parallel C compilers, macro Assembler. Also an OS, Macintosh Nubus interface card, Transputer graphics cards, a full paper copier and laserprinter. I know of dozens of successful products.

Sure you did. What were they? The only successful transputer was the T414 and it never made it outside academia.

Well, I believe there were military radar projects that shipped in reasonable quantities and served for reasonable lifetimes.

I think I remember some medical imaging products as well?

I don’t dispute that the Transputer was ultimately unsuccessful, but it wasn’t completely unused in real-world products.

See also TI’s C40, which was quite similar and similarly successful.

Re: I want a good parallel computer

#164

Post by Keyframe »

deviantbit wrote: post #59
sitkack wrote: post #58

Earlier quoted context omitted.

Those students would all drop out and start meditating. That would be a fun course. Speed run developing for all the prickly architectures of the 80s and 90s.

I see what you did there.

Guru meditation, for the uninitiated.

Re: I want a good parallel computer

#165

Post by raphlinus »

jms55 wrote: post #158
sitkack wrote: post #70

This essay needs more work. Are you arguing for a better software abstraction, a different hardware abstraction or both? Lots of esoteric machines are name dropped, but it isn't clear how that helps your argument. Why not link to Vello? https://github.com/linebender/vello I think a stronger essay would at the end give the reader a clear view of what Good means and how to decide if a machine is closer to Good than ano…

> Are you arguing for a better software abstraction, a different hardware abstraction or both? I don't speak for Raph, but imo it seems like he was arguing for both, and I agree with him. On the hardware side, GPUs have struggled with dynamic workloads at the API level (not e.g. thread-level dynamism, that's a separate topic) for around a decade. Indirect commands gave you some of that so at least the size of your da…

Absolutely. And the fact that we need to evolve both is one of the reasons progress has been difficult.

Re: I want a good parallel computer

#166

Post by petermcneeley »

IshKebab wrote: post #3

Having worked for a company that made a "hundreds of small CPUs on a single chip", I can tell you now that they're all going to fail because the programming model is too weird, and nobody will write software for them. Whatever comes next will be a GPU with extra capabilities, not a totally new architecture. Probably an nVidia GPU.

Im guessing you just dont have the computational power to compete with a real GPU. It would be relatively easy for a top end graphics programmer to write the front end graphics API for your chip. Im guessing that if they did this you would just end up with a very poor performing GPU.

Re: I want a good parallel computer

#167

Post by Animats »

jms55 wrote: post #156
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…

Fast light transport is an incredibly hard problem to solve. Raytracing (in its many forms) is one solution. Precomputing lightmaps, probes, occluder volumes, or other forms of precomputed visibility are another. In the end it comes down to a combination of target hardware, art direction and requirements, and technical skill available for each game. There's not going to be one general purpose renderer you can plug in…

The same argument could be made against Vulkan, or OpenGL, or even SQL databases. The whole NoSQL era was based on the concept that performance would be better with less generality in the database layer. Sometimes it helped. Sometimes trying to do database stuff with key/value stores made things worse.

I'm trying to find a reasonable medium. I have a hard scaling problem - big virtual world, dynamic content - and am trying to make that work well. If that works, many games with more structured content can use the same approach, even if it is overkill.

Re: I want a good parallel computer

#168

Post by Quis_sum »

Clearly the author never worked with a CM2 - I did though. The CM2 was more like a co-processor which had to be controlled by a (for that age) rather beefy SUN workstation/server. The program itself ran on the workstation which then sent the data-parallel instructions to the CM2. The CM2 was an extreme form of a MIMD design (that is why it was called data parallel). You worked with a large rectangular array (I cannot recall up to how many dimensions) which had to be a multiple of the physical processors (in your partition). All cells typically performed exactly the same operation. If you wanted to perform an operation on a subset, you had to "mask" the other cells (which were essentially idling during that time).

That is hardly what the author describes.

Re: I want a good parallel computer

#169

Post by deviantbit »

pca006132 wrote: post #126
deviantbit wrote: post #84

Earlier quoted context omitted.

So, there are books out there. I use Computer Architecture: A Quantitative Approach by Hennessy and Patterson. Recent revisions have removed historical information. I understand why they did remove it. I wanted to use Stallings book, but the department had already made arrangements with the publisher. The biggest problem on why we don't write books is that people don't buy them. They take the PDF and stick it on gith…

While financial incentives is important to some, a lot of people write books to share their knowledge and give the book out for free. I think more people are doing this now, and there are also open collaborative textbook projects. And I personally think that it is weird to write books during your working hour, and also get monet from selling that book.

"financial incentives"

This is the most ignorant response I've seen yet. We don't expect monetary gain from publishing a book. We expect our costs to be covered.

This is about the consumer, not the publisher. If we lived in a socialist system, they would still pirate our publications and we will still be in debt over it.

Re: I want a good parallel computer

#170

Post by deviantbit »

pdimitar wrote: post #134
deviantbit wrote: post #38

Earlier quoted context omitted.

Yep, transputers failed miserably. I wrote a ton a code for them. Everything had to be solved in a serial bus, which defeated the purpose of the transputer.

Quite fascinating. Did you write about your experiences in that area? Would love to read it!

Not in those terms, but an autobiography is coming, and bits and pieces are being explained. I expect about 10 people to buy the book, as all of the socialists will want it for free. I am negotiating with a publisher as we speak on the terms.
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