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Why has CPU frequency ceased to grow? (2014)

software.intel.com

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Re: Why has CPU frequency ceased to grow? (2014)

#71

Post by whoisthemachine »

My senior design course focused on asynchronous (clock-less) cryptography circuits; after learning of these, I looked into asynchronous general purpose processors, and learned that ARM actually designed an asynchronous processor back in the 2000's [0].

While they've never quite taken off (the extra gates decrease speed and our harder to manufacture), with the recent side-channel attacks on processor pipelines, I've been hopeful that I would see something pop up. Imagine a world where our processors run without a clock!

[0] https://www.eetimes.com/document.asp?doc_id=1299083

Re: Why has CPU frequency ceased to grow? (2014)

#72

Post by rcxdude »

whoisthemachine wrote: post #71

My senior design course focused on asynchronous (clock-less) cryptography circuits; after learning of these, I looked into asynchronous general purpose processors, and learned that ARM actually designed an asynchronous processor back in the 2000's [0]. While they've never quite taken off (the extra gates decrease speed and our harder to manufacture), with the recent side-channel attacks on processor pipelines, I've b…

Wouldn't asynchronous CPUs increase the amount of side-channels? AFAIK in an asynchronous circuit every aspect of the calculation may affect the time it takes to complete.

Re: Why has CPU frequency ceased to grow? (2014)

#73

Post by pjc50 »

dschuetz wrote: post #66

The rule of thumb in chip design: your chip clock is as slow as your slowest logic pipe. Complex logic circuitry slows down potential clock rates significantly. You can make your logic gates switch faster, thus allowing longer signal paths, but it has a huge energy trade-off, as the article states. Multi-core design seems now to compensate for slower clock rates, but it also has its trade-offs. It makes software more…

The RISC/CISC "tradeoff" is mostly a non-issue at the higher end of processor design: everything is now a hybrid. You have ARM64 with its SIMD and floating point extensions that hardly qualifies as "reduced" on one side, and Intel systems that have a suspiciously RISC-like internal architecture fed by decoder of the "legacy" CISC instruction set.

It still matters at the small end, which is why Cortex-M exists.

> Or do we?

A startup can design its own chips, but good luck getting anyone to use it.

Re: Why has CPU frequency ceased to grow? (2014)

#74

Post by rcxdude »

v_lisivka wrote: post #64
pjc50 wrote: post #58

Earlier quoted context omitted.

The key factors in integrated circuit delay are more to do with capacitance; in order to change a gate's transistor from off to on, the driving gate has to charge the capacitance of the driving wire and the driven gate. Making features closer together increases their mutual capacitance. (source: worked on this for a chip design software company. The delay approximation was based entirely around R/L/C modelling and ha…

I.e. the problem is the state of processor, which need to be erased. So we can make stack of stateless processors, which will readily accept fresh data, because they will need to fill capacitors only, not discharge, and then discharged after use. Kind of multicore design, but with each core used for only 1/n of time at e.g. 1Thz frequency. Unlike parallel system, sequential calculation will work faster in such setup.

discharging and charging capacitance is generally pretty symmetric. I don't think what you're suggesting would provide much benefit.

Re: Why has CPU frequency ceased to grow? (2014)

#75

Post by dschuetz »

pjc50 wrote: post #73
dschuetz wrote: post #66

The rule of thumb in chip design: your chip clock is as slow as your slowest logic pipe. Complex logic circuitry slows down potential clock rates significantly. You can make your logic gates switch faster, thus allowing longer signal paths, but it has a huge energy trade-off, as the article states. Multi-core design seems now to compensate for slower clock rates, but it also has its trade-offs. It makes software more…

The RISC/CISC "tradeoff" is mostly a non-issue at the higher end of processor design: everything is now a hybrid. You have ARM64 with its SIMD and floating point extensions that hardly qualifies as "reduced" on one side, and Intel systems that have a suspiciously RISC-like internal architecture fed by decoder of the "legacy" CISC instruction set. It still matters at the small end, which is why Cortex-M exists. > Or d…

Challenge Accepted

Re: Why has CPU frequency ceased to grow? (2014)

#76

Post by pjc50 »

whoisthemachine wrote: post #71

My senior design course focused on asynchronous (clock-less) cryptography circuits; after learning of these, I looked into asynchronous general purpose processors, and learned that ARM actually designed an asynchronous processor back in the 2000's [0]. While they've never quite taken off (the extra gates decrease speed and our harder to manufacture), with the recent side-channel attacks on processor pipelines, I've b…

One of my CS lecturers worked on this: https://www.cl.cam.ac.uk/~rja14/Papers/micromicro2003.pdf

It turns out that the advantages are not so great as might appear, and the situation gets worse as DRAM delay dominates. Also logic designers are a conservative bunch and getting everyone to replace the industry standard design toolchain is a big ask.

Re: Why has CPU frequency ceased to grow? (2014)

#77

Post by pjc50 »

v_lisivka wrote: post #64
pjc50 wrote: post #58

Earlier quoted context omitted.

The key factors in integrated circuit delay are more to do with capacitance; in order to change a gate's transistor from off to on, the driving gate has to charge the capacitance of the driving wire and the driven gate. Making features closer together increases their mutual capacitance. (source: worked on this for a chip design software company. The delay approximation was based entirely around R/L/C modelling and ha…

I.e. the problem is the state of processor, which need to be erased. So we can make stack of stateless processors, which will readily accept fresh data, because they will need to fill capacitors only, not discharge, and then discharged after use. Kind of multicore design, but with each core used for only 1/n of time at e.g. 1Thz frequency. Unlike parallel system, sequential calculation will work faster in such setup.

.. what? No, the capacitance issue is inherent in any kind of electrical signal sent over wires.

Re: Why has CPU frequency ceased to grow? (2014)

#78

Post by pjc50 »

digi_owl wrote: post #69
mjfl wrote: post #8

I took a class that went over this in depth like 3-4 years ago. Basically the message was that serial performance is saturating, and the only way to get speed improvements in the future is going to be by exploiting parallelism. However, most programmers, and programming languages, remain stuck in a serial-by-default paradigm. I'm surprised that there hasn't emerged a "parallel-by-default C++" kind of language + hardw…

I can't shake the feel that this parallelism thing will be nothing but a wild goose chase, because nature seems to be highly serial in all but the most macroscopic of senses.

All of your cells and neurons operate in parallel.

Re: Why has CPU frequency ceased to grow? (2014)

#79

Post by skrebbel »

mjfl wrote: post #8

I took a class that went over this in depth like 3-4 years ago. Basically the message was that serial performance is saturating, and the only way to get speed improvements in the future is going to be by exploiting parallelism. However, most programmers, and programming languages, remain stuck in a serial-by-default paradigm. I'm surprised that there hasn't emerged a "parallel-by-default C++" kind of language + hardw…

> Basically the message was that serial performance is saturating, and the only way to get speed improvements in the future is going to be by exploiting parallelism.

People have been warning us about this for about 10 years now, but I still don't see those 64-core CPUs I was promised anywhere.

If we had the amount of parallelism we were told we were going to get, we could give every app its own core. OSes could even consider disabling context switches altogether for the majority of apps. Instead, we're left complaining about Electron apps like it matters.

That said, I'm not sure what stagnation you refer to. There's a reason languages like Rust, Elixir/Erlang and Go are getting popular. My PHP app could handle hundreds of concurrent connections on a single machine, my Elixir app handles hundreds of thousands. Yet, processors didn't get 1000x faster (and Elixir isn't even a particularly fast language). This is the opposite of stagnation, it's progress.

Re: Why has CPU frequency ceased to grow? (2014)

#80

Post by mysterypie »

The article doesn't answer the question at the fundamental level. The closest it gets is this: "Increased frequency depends heavily on the current level of technology and advances cannot move beyond these physical limitations."

Certainly, Moore's law is just an observation and cannot go on forever. Would it fair to say that we've simply reached the point where we can no longer "keep up" with Moore's observation because the technology is getting harder and not because we've actually reached any limit of physics?

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