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The Dark Silicon Problem and What It Means for CPU Designers (2013)

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Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#11

Post by Zanni »

Phillipharryt wrote: post #7

From the article "The heat generation per unit area of an integrated circuit passed the surface of a 100-watt light bulb in the mid 1990s, and now is somewhere between the inside of a nuclear reactor and the surface of a star. " I can't tell if this is hyperbole or not, it amazes me but no amount of googling is coming up with a useful answer. Is anyone able to confirm or deny it for me?

Temperature inside a nuclear reactor: 300 degrees Celsius. [1]

Temperature on the surface of the sun: 5,600 degrees Celsius. [2]

Temperature of a CPU: ~75 degrees Celsius. [3]

[1] http://academic.brooklyn.cuny.edu/physics/sobel/Nucphys/pile...

[2] http://coolcosmos.ipac.caltech.edu/ask/7-How-hot-is-the-Sun-

[3] https://www.computerhope.com/issues/ch000687.htm

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#13

Post by jacquesm »

woah wrote: post #5
asfasgasg wrote: post #3

Earlier quoted context omitted.

If I understand correctly, neither heat dissipation nor existing manufacturing techniques are amenable to this approach. Also modern CPUs do have more than a dozen layers IIRC.

I think op is talking about 6 flat normal chips as the sides. This would allow for cooling stuff inside the cube. Maybe having only 5 of the sides as chips would make it even easier to have a heat sink. The center of the cube could be copper or something.

You can't cool from the inside of that cube without having some way of transporting the heat out of it.

All you'd end up doing is heating that inside up to the temperature of the dies and after that there would be no more cooling effect (and this would happen in a few seconds after starting the whole thing up). You could do an 'inverse' of this by cooling the dies from the outside and having the interconnects in the space in between. This would still require a lot of cooling and there would be an issue with connecting the resulting assembly to the underlying PCB.

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#14

Post by readams »

Zanni wrote: post #11
Phillipharryt wrote: post #7

From the article "The heat generation per unit area of an integrated circuit passed the surface of a 100-watt light bulb in the mid 1990s, and now is somewhere between the inside of a nuclear reactor and the surface of a star. " I can't tell if this is hyperbole or not, it amazes me but no amount of googling is coming up with a useful answer. Is anyone able to confirm or deny it for me?

Temperature inside a nuclear reactor: 300 degrees Celsius. [1] Temperature on the surface of the sun: 5,600 degrees Celsius. [2] Temperature of a CPU: ~75 degrees Celsius. [3] [1] http://academic.brooklyn.cuny.edu/physics/sobel/Nucphys/pile... [2] http://coolcosmos.ipac.caltech.edu/ask/7-How-hot-is-the-Sun- [3] https://www.computerhope.com/issues/ch000687.htm

not sure why you're being downvoted, but it's worth mentioning that the temperature is not what matters here but rather the heat generation per area. The temperature is a function of how quickly the heat can be pulled away as well as the heat generation.

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#15

Post by a_wild_dandan »

Phillipharryt wrote: post #7

From the article "The heat generation per unit area of an integrated circuit passed the surface of a 100-watt light bulb in the mid 1990s, and now is somewhere between the inside of a nuclear reactor and the surface of a star. " I can't tell if this is hyperbole or not, it amazes me but no amount of googling is coming up with a useful answer. Is anyone able to confirm or deny it for me?

(Intensity) = (Power) / (Unit Area)

(Sun's Radius) = 695 x 10^6 m

(Sun's Power) = 4 x 10^26 W

(CPU Output) = 75 W

(Die Size) = 37 mm x 37 mm

(Sun Intensity) = (4 x 10^26 W ) / (4 x pi x (695 x 10^6 m)^2) ~ 66 x 10^6

(CPU Intensity) = (75 W) / (0.0014 m^2) ~ 53 x 10^3

I'm getting a several orders of magnitude higher W/m output for the sun. Perhaps I made an algebra mistake?

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#16

Post by Zanni »

readams wrote: post #14
Zanni wrote: post #11

Earlier quoted context omitted.

Temperature inside a nuclear reactor: 300 degrees Celsius. [1] Temperature on the surface of the sun: 5,600 degrees Celsius. [2] Temperature of a CPU: ~75 degrees Celsius. [3] [1] http://academic.brooklyn.cuny.edu/physics/sobel/Nucphys/pile... [2] http://coolcosmos.ipac.caltech.edu/ask/7-How-hot-is-the-Sun- [3] https://www.computerhope.com/issues/ch000687.htm

not sure why you're being downvoted, but it's worth mentioning that the temperature is not what matters here but rather the heat generation per area. The temperature is a function of how quickly the heat can be pulled away as well as the heat generation.

Thanks for the clarification.

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#17

Post by earenndil »

Zanni wrote: post #11
Phillipharryt wrote: post #7

From the article "The heat generation per unit area of an integrated circuit passed the surface of a 100-watt light bulb in the mid 1990s, and now is somewhere between the inside of a nuclear reactor and the surface of a star. " I can't tell if this is hyperbole or not, it amazes me but no amount of googling is coming up with a useful answer. Is anyone able to confirm or deny it for me?

Temperature inside a nuclear reactor: 300 degrees Celsius. [1] Temperature on the surface of the sun: 5,600 degrees Celsius. [2] Temperature of a CPU: ~75 degrees Celsius. [3] [1] http://academic.brooklyn.cuny.edu/physics/sobel/Nucphys/pile... [2] http://coolcosmos.ipac.caltech.edu/ask/7-How-hot-is-the-Sun- [3] https://www.computerhope.com/issues/ch000687.htm

> per unit area

A CPU is a lot smaller than both a nuclear reactor and the sun.

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#18

Post by wongarsu »

blackflame7000 wrote: post #2

Why don't they start making CPUs 3 Dimensional like a cube with 6 "processors" each with multiple cores as its "sides" with the pins on the opposite sides of the cube wall. Seems to me more internal volume might allow for more cleaver head distribution channels

For heat dissipation you want the most surface area per volume (because you can only transfer heat away in the surface area). The optimal arrangement for that would be a huge, flat, one atom thick surface.

Another goal we have is low latency (and high clock rate, which is depenend on low latency), which suggests putting everything in a qube or even a shere. So we compromise somewhere in the middle with a square with a few layers.

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#19

Post by deepnotderp »

blackflame7000 wrote: post #2

Why don't they start making CPUs 3 Dimensional like a cube with 6 "processors" each with multiple cores as its "sides" with the pins on the opposite sides of the cube wall. Seems to me more internal volume might allow for more cleaver head distribution channels

1. Heat dissipation is now ~n x m times worse where n is your transistor layer count. And where m is the increased thermal resistance*

2. Power delivery is now ~n times worse where n is your transistor layer count. *

3. Connections between chips are very slow, power hungry and expensive. Fabrication of "monolithic" 3D is temperature wise painful and usually results in crummier transistors.

With that being said, innovative 3D integration methods in specific applications can help a lot. Shameless plug: we at Vathys do this for deep learning chips.

* to a first order of approximation

Re: The Dark Silicon Problem and What It Means for CPU Designers (2013)

#20

Post by deepnotderp »

blackflame7000 wrote: post #2

Why don't they start making CPUs 3 Dimensional like a cube with 6 "processors" each with multiple cores as its "sides" with the pins on the opposite sides of the cube wall. Seems to me more internal volume might allow for more cleaver head distribution channels

Such a "side cube" configuration would probably lead to longer wires than is useful.
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