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Single-chip processors have reached their limits

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Re: Single-chip processors have reached their limits

#91

Post by h2odragon »

sliken wrote: post #58
fulafel wrote: post #43

Some older stuff for reference: IBM POWER5 and POWER5+ (2004&2005) are MCM designs, had 2-4 CPU chips plus cache chips in same package. Link: https://en.wikipedia.org/wiki/POWER5

Pentium pro from 1995 had two pieces of silicon in the package: https://en.wikipedia.org/wiki/Pentium_Pro

PPros are quite hard to find now because the "gold scavengers" loved them. As i recall, at the peak in 2008, they were $100ea and more for the ceramic packages. All that interconnect was tiny gold wires, apparently.

Re: Single-chip processors have reached their limits

#92

Post by AnthonyMouse »

bob1029 wrote: post #67

Despite the limitations apparently present in single chip/CPU systems, they can still provide an insane amount of performance if used properly. There are also many problems that are literally impossible to make faster or more correct than by simply running them on a single thread/processor/core/etc. There always will be forever and ever. This is not a "we lack the innovation" problem. It's an information-theoretic /…

The alternative is speculative execution. If you can guess what the result is going to be, you can proceed to the next calculation and you get there faster if it turns out you were right.

If you have parallel processors, you can stop guessing and just proceed under both assumptions concurrently and throw out the result that was wrong when you find out which one it was. This is going to be less efficient, but if your only concern is "make latency go down," it can beat waiting for the result or guessing wrong.

Re: Single-chip processors have reached their limits

#93

Post by paulmd »

ip26 wrote: post #51
AceJohnny2 wrote: post #14

Earlier quoted context omitted.

To clarify and contextualize a bit what you're saying: The one big obstacle in creating larger chips is defects. There's just a statistical chance of there being a defect on any given surface area of the wafer, defect which generally breaks the chip that occupies that area of the wafer. So historically, the approach was to make more smaller chips and trash those chips on the wafer affected by defects. Then came the "…

The other one big obstacle is chips are square while wafers are round.

it depends on the exact shape of your mask of course, but typically losses around the edges are in the 2-3% range.

It's not really possible to fix this either since wafers need to be round for various manufacturing processes (spinning the wafer for coating or washing stages) and round obviously isn't a dense packing of the mask itself. It just kinda is how it is, square mask and round wafer means you lose a bit off the edges, fact of life.

Re: Single-chip processors have reached their limits

#94

Post by paulmd »

AceJohnny2 wrote: post #65
galaxyLogic wrote: post #57

Earlier quoted context omitted.

Sounds like a great development if it works out. But consider also that you can stick chiplets on top of each other vertically. That means you can put chiplets much closer together than if they were constrained to exist on the same single plane of the wafer. Now how about stacking wafers on top of wafers? That could be super, but there might be technical difficulties, which maybe sooner or later can be overcome.

> But consider also that you can stick chiplets on top of each other vertically. The problem there is heat dissipation. Already the performance constraint on consumer chips like the Apple M1 is how well it can dissipate heat in the product it's placed in (see Macbook Air vs Mac Mini). Stacking the chips just makes it worse.

AMD's 5800X3D and the upcoming generation of AMD/NVIDIA GPUs (both of which are rumored to feature stacked cache dies) are going to be real interesting. So far we haven't ever seen a stacked enthusiast die (MCM doesn't feature any active transistors on the interposer) and it will be interesting to see how the thermals work out.

This isn't even stacking compute dies either, stacking memory/cache is the low-hanging fruit but in the long term what everyone really wants is stacking multiple compute dies on top of each other, and that's going to get spicy real quick.

M1 is the other example but again, Apple's architecture is sort of unique in that they've designed it to run from the ground up at 3 GHz exactly, there's no overclocking/etc like enthusiasts generally expect. AMD is having to disable voltage control/overclocking on the 5800X3D as well (although that may be more related to voltage control rather than thermals - sounds like the cache die may run off one of the voltage rails from the CPU, potentially a FIVR could be used to drive that rail independently, or add an additional V_mem rail...)

And maybe that's the long-term future of things, that overclocking goes away and you just design for a tighter design envelope, one where you know the thermals work for the dies in the middle of the sandwich. Plus the Apple design of "crazy high IPC and moderately low ~3 GHz clocks" appears well-adapted for that reality.

Re: Single-chip processors have reached their limits

#95

Post by paulmd »

Iwan-Zotow wrote: post #76
AceJohnny2 wrote: post #65

Earlier quoted context omitted.

> But consider also that you can stick chiplets on top of each other vertically. The problem there is heat dissipation. Already the performance constraint on consumer chips like the Apple M1 is how well it can dissipate heat in the product it's placed in (see Macbook Air vs Mac Mini). Stacking the chips just makes it worse.

the problem is signal propagation for light to cross 1 feet should take ca 1ns

3D circuits would be denser (shorter propagation distances) than a planar circuit. In fact "computronium" is sort of an idea about how dense you can conceptually make computation.

You just can't really cool it that well with current technologies. Microfluidics are the current magic wand that everyone wishes existed but it's a ways away yet.

Re: Single-chip processors have reached their limits

#97

Post by sliken »

h2odragon wrote: post #91
sliken wrote: post #58

Earlier quoted context omitted.

Pentium pro from 1995 had two pieces of silicon in the package: https://en.wikipedia.org/wiki/Pentium_Pro

PPros are quite hard to find now because the "gold scavengers" loved them. As i recall, at the peak in 2008, they were $100ea and more for the ceramic packages. All that interconnect was tiny gold wires, apparently.

Heh, had no idea, they seemed to have a pretty limited run, ran at up 200 MHz, but was pretty quickly replaced by a Pentium-II at 233 Mhz on a single die.

Re: Single-chip processors have reached their limits

#98

Post by tsimionescu »

AnthonyMouse wrote: post #92
bob1029 wrote: post #67

Despite the limitations apparently present in single chip/CPU systems, they can still provide an insane amount of performance if used properly. There are also many problems that are literally impossible to make faster or more correct than by simply running them on a single thread/processor/core/etc. There always will be forever and ever. This is not a "we lack the innovation" problem. It's an information-theoretic /…

The alternative is speculative execution. If you can guess what the result is going to be, you can proceed to the next calculation and you get there faster if it turns out you were right. If you have parallel processors, you can stop guessing and just proceed under both assumptions concurrently and throw out the result that was wrong when you find out which one it was. This is going to be less efficient, but if your…

Not necessarily. There are problems you can't speed up even if you are given a literal infinity of processors - the problems in EXP for example (well, EXP - NP). Even for NP problems, the number of processors you need for a meaningful speed up grows proportionally to the size of the problem (assuming P!=NP).

Re: Single-chip processors have reached their limits

#99

Post by AnthonyMouse »

tsimionescu wrote: post #98
AnthonyMouse wrote: post #92

Earlier quoted context omitted.

The alternative is speculative execution. If you can guess what the result is going to be, you can proceed to the next calculation and you get there faster if it turns out you were right. If you have parallel processors, you can stop guessing and just proceed under both assumptions concurrently and throw out the result that was wrong when you find out which one it was. This is going to be less efficient, but if your…

Not necessarily. There are problems you can't speed up even if you are given a literal infinity of processors - the problems in EXP for example (well, EXP - NP). Even for NP problems, the number of processors you need for a meaningful speed up grows proportionally to the size of the problem (assuming P!=NP).

Computational complexity and parallelism are orthogonal. Many EXP algorithms are embarrassingly parallel. You still have to do 2^n calculations, but if you have 1000 processors then it will take 1000 times less wall clock time because you're doing 1000 calculations at once.

The reason parallelism doesn't "solve" EXP problems is that parallelism grows linearly against something whose time complexity grows exponentially. It's not that it doesn't work at all, it's that if you want to solve the problem for 2n in the same time as for n, you need to double the number of processors. So the number of processors you need to solve the problem in whatever you define as a reasonable amount of time grows exponentially with n, but having e.g. 2^n processors when n is 1000 is Not Gonna Happen.

Having 1000 processors will still solve the problem twice as fast as 500, but that's not much help in practice when it's the difference between 50 billion billion years and 100.

Re: Single-chip processors have reached their limits

#100

Post by touisteur »

sliken wrote: post #56
2OEH8eoCRo0 wrote: post #16

Earlier quoted context omitted.

> The M1 Ultra is fabricated as a single chip. I'm curious how much the M1 Ultra costs. It's such a massive single piece of glass I'd guess it's $1,200+. If that's the case it doesn't make sense to compare the M1 Ultra to $500 CPUs from Intel and AMD.

Dunno, M1 Ultra includes a decent GPU, which the $500 CPUs from Intel and AMD do not. Seems relatively comparable to a $700 GPU (like a RTX 3070 if you can find one) depending on what you are using. Sadly metal native games are rare, many use some metal wrapper and/or Rosetta emulation. Seems pretty fair to compare an Intel alder lake or higher end AMD Ryzen AND a GPU (rtx 3070 or radeon 6800) to the M1 ultra, assumi…

Has anyone managed to reach the actual advertised 21 FP32 TFLOPS? I'm curious. Even BLAS or pure custom matmul stuff? How much of that is actually available? I can almost saturate and sustain an NVIDIA A40 or A4000 to their peak perf, so, wondering whether anyone written something there?
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