5 ms·

Overclocking isn't just limited by heat dissipation, and dealing with the additional heat generation is one of the easier issues to overcome. Much more limiting

by chias 5y ago

Overclocking isn't just limited by heat dissipation, and dealing with the additional heat generation is one of the easier issues to overcome. Much more limiting is the fact that the electronic components in the hardware (everything from RAM to the more "integrated" components on the PCBs) have certain amounts of time which they need to take in order to tie voltages high or low, to either read or output a bit. This amount of time is typically very small as compared to the amount of time that a voltage stays tied high or low, and so isn't a problem, but while you can shorten the amount of time that a voltage needs to stay high or low when overclocking, generally the transition time isn't as negotiable. Increasing clock speeds to the point where these transition times dominate means you're going to get garbage reads and garbage writes out of a component. This is part of why if you're overclocking your computer, you end up experiencing errors or unexpected crashes even when temperature doesn't go too high. Past reasonable tolerances, you can't just cool it more and expect it to work.

nielsbot 5y ago
cryogenic cooling tho?
- chias 5y ago
  Wouldn't solve the problem. Basically you need the integrated components to have shorter transition times. These are an inherent property of the component: speeding up the transition time basically means "replace this component with a different component that has a shorter transition time"
  - dragontamer 5y ago
    Overvolting the component and sending more current to any transistor tends to speed it up, though at the cost of severely more watts used. Overclocking is often a combination of overvolting (leading to more amps), allowing you to increase clock speeds.
    - bserge 5y ago
    - chias 5y ago
      As they say, "the candle that burns twice as bright burns half as long", or, in this case, "the transistor that runs at thrice the voltage runs for about 1.3 seconds"
  - R0b0t1 5y ago
    Overvolting is how this is solved and works with adequate cooling.
- zeusk 5y ago
  Google propogation delay, your pipeline's length and delay of devices within that pipe determine the max frequency your circuit can run at (a very high level overview).
  - kingosticks 5y ago
    How is pipeline length related to max frequency?
    - enchiridion 5y ago
      Physical length the signal has to travel.
    - amluto 5y ago
      It’s related indirectly. A longer pipeline tends to result in shorter stages within the pipeline. (This is the whole point of pipelining.)
      - kingosticks 5y ago
        OK, yes there's often correlation but that's it. A longer pipeline doesn't affect max circuit frequency. The other sibling comment regarding distance isn't true. regardless of how insane your feedbacks are. Physical placement tools have always handled this in my experience (as a chip designer for 10+ years).
        deleted 5y ago
        [deleted]
        u320 5y ago
        There is no point of lengthening the pipeline if you don't get higher frequency from it. It would just add complexity and and a higher branch mispredict penalty.
        deleted 5y ago
        [deleted]
timpattinson 5y ago
It's not like Apple would ever do it, but the M1 should have heaps of OC headroom. Given that the RAM is already on package, all they need to do is turn up the CPU multiplier. AMD chips are doing similar clocks to Intel on TSMC N7, so Apple could (but won't) have a chip running way higher than the clocks they are currently shipping with. Also, it's kinda inaccurate to imply any overclocked setup will crash, there's plenty of room unless they come turned up to the max from stock like the 12900k.
- marcan_42 5y ago
  The M1 family already can only sustain 3.2GHz with only one core per cluster active, so there is some bottleneck there, either due to power dissipation/density or power delivery. If the latter, upping the voltage would give you more oomph, but that comes with diminishing returns. I wouldn't expect Apple to give the chips more than a trivial clock bump (3.4?) this generation, if that.
- throwawaylinux 5y ago
  Overclocking headroom means you have timing slack, and timing slack means you have faster ~= leakier circuits than necessary, or stages which aren't filled with work which is also an inefficiency. I expect Apple has an extreme focus on power efficiency and especially idle / leakage power, much more than Intel considering the core basically the same as they use in their phones. They also have a different approach to turbo / dvfs. So I would expect M1 to actually be a lot tighter than Intel and not have so much OC headroom. Obviously you can buy timing with voltage to some degree, so there would be something there probably. Modern nodes are running into more problems with voltage induced breakdown though so the OC limit looks very different to what you can ship in a product. Has anyone measured M1's VDD? > AMD chips are doing similar clocks to Intel on TSMC N7, so Apple could (but won't) have a chip running way higher than the clocks they are currently shipping with. Not their existing microarchitecture though. They do nearly 2x the work per clock as AMD chips which necessitates more logic per stage. Getting a microarchitectural edge means making less logic do more work and it's very possible Apple have some edge there, it just wouldn't be near 2x IMO. The silicon technology of course plays into it, but when you look at how fast individual transistors and the shortest poly to connect them can switch, speeds over 100GHz have been possible on 90nm. Today's cutting edge is probably over 200GHz (e.g., search ring oscillator). So it's not a fundamental switching speed limit of the tech that gets you. I would say Apple could probably redo the physical design and synthesis work and minimal logic changes to target a faster and leakier device that's not suitable for phones but might be a little fairer comparison. It wouldn't put it at a 5-6GHz frequency, but could easily be enough to re-take these benchmarks and still be ahead on efficiency.
klodolph 5y ago
Transition times decrease as voltage increases. The amount of power being dissipated is roughly proportional to V^2 f, and V is roughly proportional to f, so the tradeoff kinda sucks (double frequency = 8x power consumption), but you can eke out some additional performance if you are willing to dissipate more heat, within limits.
omegalulw 5y ago
> have certain amounts of time which they need to take in order to tie voltages high or low, to either read or output a bit. When you overclock you add voltage which helps with this which goes a long way. You would often hit thermal limits first, so heat dissipation is a major factor.
- bayindirh 5y ago
  This is not my experience in the olden Athlon XP days. Even though you give the extra voltage and give enough cooling, the CPU starts to encounter many internal errors and needs to re-run a lot of instruction trains to get sane results. This causes heat and load spikes, and while you get no errors, the increased frequency doesn't give you any real world performance gains. Returning a to a slower configuration actually gives a much snappier and performant system.
  - zht 5y ago
    Athlon was 20 years ago. It feels unfair to generalize across time and architectures
    - bayindirh 5y ago
      It's not about architecture. It's about physics. Once you pass a certain threshold, electron/current leaks and escapes start to wreak havoc inside any silicon. So beyond voltage, current and temperature, you're limited by the silicon itself. I stopped overclocking systems after Athlon XP. This is why I gave that example. Even without overclocking and overheating, I've seen and still seeing partially cooked processors which shut-down half of their FPU pipelines to stay reliable albeit with orders of magnitude lower performance. CPUs are much more complex with their MCE and more advanced microcode structures ever, and there's much more than meets the eye.
jorvi 5y ago
> This is part of why if you're overclocking your computer, you end up experiencing errors or unexpected crashes even when temperature doesn't go too high. Past reasonable tolerances, you can't just cool it more and expect it to work. People push CPUs to absurd limits with LN2 cooling so they’d just not true.

by chias 5y ago

nielsbot 5y ago

cryogenic cooling tho?

chias 5y ago
Wouldn't solve the problem. Basically you need the integrated components to have shorter transition times. These are an inherent property of the component: speeding up the transition time basically means "replace this component with a different component that has a shorter transition time"
- dragontamer 5y ago
  Overvolting the component and sending more current to any transistor tends to speed it up, though at the cost of severely more watts used. Overclocking is often a combination of overvolting (leading to more amps), allowing you to increase clock speeds.
  - bserge 5y ago
  - chias 5y ago
    As they say, "the candle that burns twice as bright burns half as long", or, in this case, "the transistor that runs at thrice the voltage runs for about 1.3 seconds"
- R0b0t1 5y ago
  Overvolting is how this is solved and works with adequate cooling.
zeusk 5y ago
Google propogation delay, your pipeline's length and delay of devices within that pipe determine the max frequency your circuit can run at (a very high level overview).
- kingosticks 5y ago
  How is pipeline length related to max frequency?
  - enchiridion 5y ago
    Physical length the signal has to travel.
  - amluto 5y ago
    It’s related indirectly. A longer pipeline tends to result in shorter stages within the pipeline. (This is the whole point of pipelining.)
    - kingosticks 5y ago
      OK, yes there's often correlation but that's it. A longer pipeline doesn't affect max circuit frequency. The other sibling comment regarding distance isn't true. regardless of how insane your feedbacks are. Physical placement tools have always handled this in my experience (as a chip designer for 10+ years).
      - deleted 5y ago
        [deleted]
      - u320 5y ago
        There is no point of lengthening the pipeline if you don't get higher frequency from it. It would just add complexity and and a higher branch mispredict penalty.
        deleted 5y ago
        [deleted]

timpattinson 5y ago

It's not like Apple would ever do it, but the M1 should have heaps of OC headroom. Given that the RAM is already on package, all they need to do is turn up the CPU multiplier. AMD chips are doing similar clocks to Intel on TSMC N7, so Apple could (but won't) have a chip running way higher than the clocks they are currently shipping with. Also, it's kinda inaccurate to imply any overclocked setup will crash, there's plenty of room unless they come turned up to the max from stock like the 12900k.

marcan_42 5y ago
The M1 family already can only sustain 3.2GHz with only one core per cluster active, so there is some bottleneck there, either due to power dissipation/density or power delivery. If the latter, upping the voltage would give you more oomph, but that comes with diminishing returns. I wouldn't expect Apple to give the chips more than a trivial clock bump (3.4?) this generation, if that.
throwawaylinux 5y ago
Overclocking headroom means you have timing slack, and timing slack means you have faster ~= leakier circuits than necessary, or stages which aren't filled with work which is also an inefficiency. I expect Apple has an extreme focus on power efficiency and especially idle / leakage power, much more than Intel considering the core basically the same as they use in their phones. They also have a different approach to turbo / dvfs. So I would expect M1 to actually be a lot tighter than Intel and not have so much OC headroom. Obviously you can buy timing with voltage to some degree, so there would be something there probably. Modern nodes are running into more problems with voltage induced breakdown though so the OC limit looks very different to what you can ship in a product. Has anyone measured M1's VDD? > AMD chips are doing similar clocks to Intel on TSMC N7, so Apple could (but won't) have a chip running way higher than the clocks they are currently shipping with. Not their existing microarchitecture though. They do nearly 2x the work per clock as AMD chips which necessitates more logic per stage. Getting a microarchitectural edge means making less logic do more work and it's very possible Apple have some edge there, it just wouldn't be near 2x IMO. The silicon technology of course plays into it, but when you look at how fast individual transistors and the shortest poly to connect them can switch, speeds over 100GHz have been possible on 90nm. Today's cutting edge is probably over 200GHz (e.g., search ring oscillator). So it's not a fundamental switching speed limit of the tech that gets you. I would say Apple could probably redo the physical design and synthesis work and minimal logic changes to target a faster and leakier device that's not suitable for phones but might be a little fairer comparison. It wouldn't put it at a 5-6GHz frequency, but could easily be enough to re-take these benchmarks and still be ahead on efficiency.

klodolph 5y ago

Transition times decrease as voltage increases. The amount of power being dissipated is roughly proportional to V^2 f, and V is roughly proportional to f, so the tradeoff kinda sucks (double frequency = 8x power consumption), but you can eke out some additional performance if you are willing to dissipate more heat, within limits.

omegalulw 5y ago

> have certain amounts of time which they need to take in order to tie voltages high or low, to either read or output a bit. When you overclock you add voltage which helps with this which goes a long way. You would often hit thermal limits first, so heat dissipation is a major factor.

bayindirh 5y ago
This is not my experience in the olden Athlon XP days. Even though you give the extra voltage and give enough cooling, the CPU starts to encounter many internal errors and needs to re-run a lot of instruction trains to get sane results. This causes heat and load spikes, and while you get no errors, the increased frequency doesn't give you any real world performance gains. Returning a to a slower configuration actually gives a much snappier and performant system.
- zht 5y ago
  Athlon was 20 years ago. It feels unfair to generalize across time and architectures
  - bayindirh 5y ago
    It's not about architecture. It's about physics. Once you pass a certain threshold, electron/current leaks and escapes start to wreak havoc inside any silicon. So beyond voltage, current and temperature, you're limited by the silicon itself. I stopped overclocking systems after Athlon XP. This is why I gave that example. Even without overclocking and overheating, I've seen and still seeing partially cooked processors which shut-down half of their FPU pipelines to stay reliable albeit with orders of magnitude lower performance. CPUs are much more complex with their MCE and more advanced microcode structures ever, and there's much more than meets the eye.

jorvi 5y ago

> This is part of why if you're overclocking your computer, you end up experiencing errors or unexpected crashes even when temperature doesn't go too high. Past reasonable tolerances, you can't just cool it more and expect it to work. People push CPUs to absurd limits with LN2 cooling so they’d just not true.