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Xbox 360 Architecture

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Re: Xbox 360 Architecture

#61

Post by fulafel »

bee_rider wrote: post #37
bombcar wrote: post #21

Earlier quoted context omitted.

The "compiler will solve everything" theory seemed to last quite a long time, I first heard it with the Itanium and again with these pipelined CPUs. Narrator: It didn't solve anything.

This is speculation, but: optimizing compilers are pretty good, right? On x86 at least. Perhaps they do a good job on popular platforms like x86, because we can encode decades of experience, but not so great on brand new ones.

Everything is relative. They do things that seemed quite neat in the 90s, but then progress slowed to a crawl.

I'd call the state of the field quite bad. For example they do embarrassingly little for you to help with the 2 main bottlenecks we've had for a long time: concurrency and data layout optimization. And for even naive model (1 cpu / free memory) there is just so much potentially automateable manual toil in doing semantics based transformations in perf work that it's not even funny.

A large part is using languages that don't support these kinds of optimizations. It's not "C compiler improvements hit a wall", it continues "and we didn't develop & migrate to languages whose semantics allow optimizations". (There's a little of this in the GPU world, but the proprietary infighting there has produced a dev experience and app platform so bad that very few apps outside games venture there)

There's a whole alternative path of processor history not taken in the case that VLIW had panned out, and instead of failing because of optimism about compiler optimizations.

Re: Xbox 360 Architecture

#62

Post by flipacholas »

Arrath wrote: post #53
anyfoo wrote: post #50

Earlier quoted context omitted.

> I am curious though, other that one brief mention, why didn't you touch on the early hardware reliability issues at all? I guess because they likely didn't have anything to do with the architecture? Or were there really reliability issues that were a result of the architecture, instead of physical/electrical hardware issues?

Fair. I was thinking in terms of the physical architecture of the boards, cooling solutions, and entire consoles rather than the pure architecture of the cpu, gpu, etc.

Yeah, it was mainly because the article got too long, so I had no option but to draw the line somewhere. There's still a tiny mention at the footer below the main motherboard image:

> Showing the 'Xenon' revision (the first one), taken from my model from 2005. Xenon motherboards are also famous for being defective by design (they get too hot to play games with!). Remaining GDDR3 chips are found on the back.

Btw, I've replaced the bad links with archived ones. I triggered an archive of that site back in December just in case such great source would disappear, never expected to happen just after releasing the article!

Re: Xbox 360 Architecture

#63

Post by flipacholas »

gwern wrote: post #36
flipacholas wrote: post #2

Hi Hackernews, don't forget you can use the alternative edition without styles: https://classic.copetti.org/writings/consoles/xbox-360/ (works better with accessibility tools, like text to speech; and translators) There are also new PDF and EPUB editions here: https://www.patreon.com/posts/67035520 (it's a public post, I just needed a place to upload those files without consuming my hosting's bandwidth). If you spot…

One obvious thing you could do to conserve bandwidth is not do loading=auto but loading=lazy. You've got like 70 images in there which are going to download, but how many readers will scroll to the bottom and look at all 70? (Few.)

Oh, this is actually a bug of the html template, until now I've never realised it was happening. I've just fixed it, thanks.

Re: Xbox 360 Architecture

#64

Post by flipacholas »

Jerrrry wrote: post #18

This is beautiful. I wish I could remember enough to contribute, especially to the DEV/XBL online chapters. If I ever recover my old /modding/ folder, I will reach out [OP]. I was pseudo-privy to a lot of non-public stuff that I think the public could benefit now from, with a decade passing, I think it would be be appropriate to share.

Much appreciated

Re: Xbox 360 Architecture

#65

Post by commandersaki »

landr0id wrote: post #29

Super minor nitpick but ROP wasn’t used for the King Kong/SMC exploit. I would consider it a ROP exploit if multiple return-oriented gadgets were chained together to form a full exploit chain, but what happened here is the syscall handler was invoked with a malformed index causing a single jump to user-mode code with kernel-mode privileges. It’s not too dissimilar to calling an arbitrary function pointer. Otherwise t…

I think it was also the first to see a HMAC timing side channel exploit in the wild.

Re: Xbox 360 Architecture

#66

Post by delta_p_delta_x »

Veliladon wrote: post #38
bee_rider wrote: post #37

Earlier quoted context omitted.

This is speculation, but: optimizing compilers are pretty good, right? On x86 at least. Perhaps they do a good job on popular platforms like x86, because we can encode decades of experience, but not so great on brand new ones.

One thing that Intel and AMD do better than any other player in the industry is branch prediction. An absolutely stupifying amount of die area is dedicated to it on x86. Combining this with massive speculative execution resources and you can get decent ILP even out of code that's ridiculously hostile to ILP. Our modern CPU cores have hundreds of instructions in flight at any one moment because of the depth of OoO exe…

> One thing that Intel and AMD do better than any other player in the industry is branch prediction. An absolutely stupifying amount of die area is dedicated to it on x86.

Zen in particular combines an L1 perceptron and L2 TAGE[0] predictor[1]. TAGE in particular requires an immense amount of silicon, but it has something like 99.7% prediction accuracy, which is... crazy. The perceptron predictor is almost as good: 99.5%.

I wrote a software TAGE predictor, but too bad it didn't perform as well as predicted (heh) by the authors of the paper.

[0]: https://doi.org/10.1145/2155620.2155635 [1]: https://fuse.wikichip.org/news/2458/a-look-at-the-amd-zen-2-...

Re: Xbox 360 Architecture

#67

Post by ace2358 »

HyprMusic wrote: post #20

Wow what a journey the homebrew section of that article was. As someone who grew up heavily involved in the evolving Xbox homebrew scene, I dipped out of consoles before the 360 was truly cracked. I remember the sadness in realising the DVD drive exploit had effectively killed off any interest in trying to run homebrew, but I'm thoroughly glad to learn that the community not only persisted, but became incredibly inve…

I can relate. I had a modded dvd drive. Got banned after a year maybe. Loved playing gears online.

Then I think it got the red ring? That was the end for me. Only recently got into gaming a bit more now. I still like how consoles are mostly set and forget compared to pc based gaming. Looks like the ps4 is getting homebrew which is interesting as it is basically a pc?

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