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Nvidia R&D chief on how AI is improving chip design

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Re: Nvidia R&D chief on how AI is improving chip design

#41

Post by bsder »

jiggawatts wrote: post #33
bsder wrote: post #10

What is extremely telling is what is missing ... Design Rule Checking (DRC) and Layout Vs Schematic (LVS). These require: 1) Longer bit length arithmetic 32-bit float simply isn't enough. 64-bit float is close, but limited. You really want 128-bit integer. And nVidia isn't delivering that. 2) Real algorithmic improvements We're still stuck with computational geometry algorithms that don't parallelize. It would be awf…

Can you explain why such large numbers are required? Back-of-the-napkin maths is that a chip that is 3cm on each side -- which is huge -- can be subdivided into 0.007 nanometre increments using 32 bit integers. That's 1/7th of the diameter of a hydrogen atom! The resolution with 64-bit floats (let alone integers) would be absurd, roughly a million times finer-grained still. That's probably enough to simulate individu…

> Can you explain why such large numbers are required?

Absolutely.

Even if you start with 32 bits, you often have polygons with many sides. In the worst case, you are modeling a "circle" and have to increase your precision to enough level to be accurate (please note that nobody in the right mind in VLSI would ever draw a "circle"--however, you wind up with an "implied" one due to DRC, more down below ...)

The problem is that line sweep intersection checks in DRC require approximately 3n+a couple bits to differentiate intersections that may be close to degenerate or have multple intersections near to each other. So, if you start with 32-bit numbers, you require approximately 96 bits plus a little for your intermediate calculations. (See: Hobby -- "Practical segment intersection with finite precision output" -- I'll let people find their own copy of the paper so HN doesn't splatter some poor site that I link)

You would think that doesn't matter since VLSI tends to limit itself to rectilinear and 45 degree angles. Unfortunately life isn't that simple.

If you take a simple rectangle and say "Nothing can be within distance x", you get a slightly larger rectangle parallel to the sides. Easy. The problem is that you also wind up with an implied quarter circle (told you this would come back) near each corner. Not so easy.

Put those circles such that they overlap only very slightly and you may have segments that are pretty close to tangent. Super not easy. Unfortunately, VLSI design often consists of putting those metals such that they are riiiight at the limit of spacing. Consequently, your super-not-easy case also becomes a very common case. Ouch.

Of course, you could just move the rectangle completely outward so that you have squares at the corners. However, that gives up a non-trivial amount of area that most places aren't willing to concede.

There is a reason why Siemens (nee Mentor) Calibre is so egregiously expensive.

Re: Nvidia R&D chief on how AI is improving chip design

#42

Post by selimthegrim »

maxwells-daemon wrote: post #36

I work on this team! (Specifically: applied deep learning research, chip design). It's a shame to see so many people dismissing this work as marketing. I see lots of clever people working hard on really novel and interesting stuff, and I really do think that ML has real potential to customize a design much more "deeply" than traditional automation tools.

Ha, this does sound awesome. Are you guys hiring?

Re: Nvidia R&D chief on how AI is improving chip design

#43

Post by jiggawatts »

bsder wrote: post #41
jiggawatts wrote: post #33

Earlier quoted context omitted.

Can you explain why such large numbers are required? Back-of-the-napkin maths is that a chip that is 3cm on each side -- which is huge -- can be subdivided into 0.007 nanometre increments using 32 bit integers. That's 1/7th of the diameter of a hydrogen atom! The resolution with 64-bit floats (let alone integers) would be absurd, roughly a million times finer-grained still. That's probably enough to simulate individu…

> Can you explain why such large numbers are required? Absolutely. Even if you start with 32 bits, you often have polygons with many sides. In the worst case, you are modeling a "circle" and have to increase your precision to enough level to be accurate (please note that nobody in the right mind in VLSI would ever draw a "circle"--however, you wind up with an "implied" one due to DRC, more down below ...) The problem…

Disclaimer: I have zero silicon design experience.

However, I have designed computer game engines that use 32-bit floats throughout and encountered rounding errors in practice.

I’ve found that there’s always a solution that avoids the need to go past 64 bits, and even that is a last resort.

So for example the circle could be approximated with a polygon. Or fixed-point arithmetic can be used. Or simply use a quad-tree or related space partitioning algorithms to check for intersections.

There are literally thousands of algorithms that sidestep these issues and are used extensively in computer games, typically at 32-bit precision exclusively.

For example “back in the day” you would often see shimmering due to “z-fighting”. You would also often see white pixels due to “cracks” between adjacent polygons.

All of these are largely gone now. The problems have been solved without the enormous performance hit of 64-bit doubles, let alone 128!

Meanwhile contemporary CAD programs would insist on using 64-bit doubles, even through the OpenGL pipeline out to the screen.

But if you sit down for a second and just divide your screen (or wafer mask) by the range of your chosen numbers you’ll instantly see that you have thousands of steps per pixel (or atom!) to work with.

Any visible noise is your fault for choosing the wrong algorithm, not the fault of the hardware for not providing enough bits.

Re: Nvidia R&D chief on how AI is improving chip design

#44

Post by marginalia_nu »

maxwells-daemon wrote: post #36

I work on this team! (Specifically: applied deep learning research, chip design). It's a shame to see so many people dismissing this work as marketing. I see lots of clever people working hard on really novel and interesting stuff, and I really do think that ML has real potential to customize a design much more "deeply" than traditional automation tools.

This is directed at AI marketing in general: "AI" has been used to market so much nonsense it's probably becoming a problem communicating actual interesting uses of AI. I very much get a dot com vibe off it, like nobody on the team knows how it works but we're sure we're gonna be rich somehow! In my head, I've begun substituting AI with "wizards" when I read it.

It's very much the sort of problems crypto is having. So many grifters actual interesting uses of the technology are very hard to identify and take seriously.

Re: Nvidia R&D chief on how AI is improving chip design

#45

Post by andrepd »

blihp wrote: post #13
rektide wrote: post #5

Earlier quoted context omitted.

> Do you have an example of a company releasing an open source version of their secret sauce? The chip design itself should be the secret sauce. Not the tools you make the chip with. Nvidia is resolutely not-contributing. Many other companies are starting to get onboard with open chip design. This doesn't mean the chips have to be open, but the tooling needs to be something shared & co-developable. If this is a littl…

> The chip design itself should be the secret sauce. Not the tools you make the chip with. The secret sauce is generally whatever gives one a competitive advantage. Businesses typically open things up when the want to reduce the cost of something and/or cause pain for someone else (i.e. killing their cash cow), not because they're benevolent and want to share. > I challenge you to answer your own question in reverse:…

The GP said nothing about "benevolence", he was arguing it is in the interest of NVidia

Re: Nvidia R&D chief on how AI is improving chip design

#46

Post by ImportOllie »

I don't understand the backlash here. The jist seemed to be traditional tools that are exact take a long time to process complex designs. Deep learning offers a statistical approach that can give a 'coarse' prediction and they're using this to reduce development time. That seems to make sense to me, especially in the earlier verification phases of the hardware design lifecycle.

To me this sounds like a good use-case of AI and Neural Nets. It doesn't appear to be looking to replace the traditional tools, just augment.

Re: Nvidia R&D chief on how AI is improving chip design

#47

Post by jiggawatts »

qayxc wrote: post #35
jiggawatts wrote: post #33

Earlier quoted context omitted.

Can you explain why such large numbers are required? Back-of-the-napkin maths is that a chip that is 3cm on each side -- which is huge -- can be subdivided into 0.007 nanometre increments using 32 bit integers. That's 1/7th of the diameter of a hydrogen atom! The resolution with 64-bit floats (let alone integers) would be absurd, roughly a million times finer-grained still. That's probably enough to simulate individu…

> The resolution with 64-bit floats (let alone integers) would be absurd, roughly a million times finer-grained still. Careful there! Floating point numbers do not form a proper field, not even a semi-group. Due to the uneven distribution of elements, the field axioms don't hold (e.g. both commutativity and distributivity can be violated) and great care has to be taken to assure the numeric stability of computations.

My physics professor had some good examples of how numeric precision vastly outstrips reality: if modelling a 1m iron bar using 32-bit numbers, the error in length is substantially less than a dust mote landing on the end of it. It's about the same as a virus (not a bacterium) on the end... or not. The oil from a fingerprint is thicker. The mere presence of a human in the room will warm up the iron rod enough to cause it to expand more than this.

You only get physically significant errors when using iterated algorithms where the errors accumulate, or when doing what amounts to equality comparisons, which is almost always an error.

Note that 64-bit numbers aren't "twice" as precise.[1] They're four billion times more precise. Going to 128 bits is absurd beyond belief. Numbers like these would allow the entire visible universe to be modelled, down to the width of a proton. You do not need 128 bit numbers for anything made on Earth, by humans, ever. If you think you do, you've made a mistake. It's as simple as that.

[1] floating point numbers and integers are obviously different, but the concepts are the same. A 64-bit double is "just" 536 million times more precise that a 32-bit float, but that is still an awful lot of precision for anything made of matter...

Re: Nvidia R&D chief on how AI is improving chip design

#48

Post by kevincox »

productceo wrote: post #20

Please keep up the processing power progress! Economics of the software industry (or at least the products that I work on) depend on the assumption that cost of computing (including storage) diminish exponentially over time! <3

You say this like it is a good thing. It seems to me that if a whole industry is dependant on exponential growth of another than the former is being quite reckless.

Of course exponential growth will help, but relying on it seems like a bit too much risk.

Re: Nvidia R&D chief on how AI is improving chip design

#49

Post by hurflmurfl »

kevincox wrote: post #48
productceo wrote: post #20

Please keep up the processing power progress! Economics of the software industry (or at least the products that I work on) depend on the assumption that cost of computing (including storage) diminish exponentially over time! <3

You say this like it is a good thing. It seems to me that if a whole industry is dependant on exponential growth of another than the former is being quite reckless. Of course exponential growth will help, but relying on it seems like a bit too much risk.

I think that's the point GP is making with his sarcastic remark :)

Re: Nvidia R&D chief on how AI is improving chip design

#50

Post by gchadwick »

bsder wrote: post #41
jiggawatts wrote: post #33

Earlier quoted context omitted.

Can you explain why such large numbers are required? Back-of-the-napkin maths is that a chip that is 3cm on each side -- which is huge -- can be subdivided into 0.007 nanometre increments using 32 bit integers. That's 1/7th of the diameter of a hydrogen atom! The resolution with 64-bit floats (let alone integers) would be absurd, roughly a million times finer-grained still. That's probably enough to simulate individu…

> Can you explain why such large numbers are required? Absolutely. Even if you start with 32 bits, you often have polygons with many sides. In the worst case, you are modeling a "circle" and have to increase your precision to enough level to be accurate (please note that nobody in the right mind in VLSI would ever draw a "circle"--however, you wind up with an "implied" one due to DRC, more down below ...) The problem…

Of course when you're doing such intersection calculations you know the things you're intersecting are very close. You don't need a general method that can test arbitrarily sized and spaced polygons against each other. You need a method to determine what is sufficiently close to each other to be worthy of a more detailed check. Then a more specific method to do this check.

You could use 32 bit integers with all shapes specified vs say a 0.1 nm grid giving you around a maximum 0.4m x 0.4m chip size which seems ample. Then when you want to check for rules violations in the cases like you specify with very fine precision use a dedicated check that can assume the relevant geometry is within a small number of grid points of each other. For example the check could work using relative coordinates rather than absolute so say switch to a grid on a 0.00001nm basis (to pull an arbitrary precision out of a hat) and convert the 32-bit absolute 0.1nm coords to relative 32-bit 0.00001nm coords.

Easier said then done to be sure (as you say the tools are egregiously expensive!) but just saying I need a 64-bit or a 128-bit float isn't trying to get to the grips with the problem, just hoping you wave it away with more bits.

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