8 ms·

> The so-called TDP of the Ryzen 9950X is 170W. The used heat sinks are specified to dissipate 165W, so that seems tight. TDP numbers are completely made up. T

by db48x 1y ago

> The so-called TDP of the Ryzen 9950X is 170W. The used heat sinks are specified to dissipate 165W, so that seems tight. TDP numbers are completely made up. They don’t correspond to watts of heat, or of anything at all! They’re just a marketing number. You can't use them to choose the right cooling system at all. https://gamersnexus.net/guides/3525-amd-ryzen-tdp-explained-deep-dive-cooler-manufacturer-opinions https://gamersnexus.net/guides/3525-amd-ryzen-tdp-explained-...

einpoklum 1y ago
Wow, I can't believe how BS this TDP is! I feel like a total idiot! I've always assumed it's sorta-kinda a tight upper bound on power consumption, perhaps with some allowance for "imperfections" in the dissipation properties of the CPU, and that I shouldn't sweat the details. Couldn't this count as false/misleading advertizing though?
- vel0city 1y ago
  Its pretty insane to see someone say something like: “TDP is about thermal watts, not electrical watts. These are not the same.” Watts are watts. But yeah, TDP means nothing. If you stick plenty of cooling and run the right motherboard board revision your "TDP" can be whatever you want it to be until the thing melts.
  - o11c 1y ago
    "TDP is about average watts, not peak watts" would be an honest way of saying it.
    - vel0city 1y ago
      But in the end that's still not actually true in many modern desktop chips. You can take a 65W part, and with a "stock" motherboard firmware, good cooling, and the right workload end up averaging way more than 65W. Or if you have it in a hot room it just might end up using less than 65W. TDP is more of a rough idea of how much power the manufacturer wanted to classify the part as. It ultimately only loosely relates to the actual heat or electrical usage in practice.
- gruez 1y ago
  It's thermal design power, ie. it's the power that it's designed for, not absolute max.
  - db48x 1y ago
    No, they don’t design the chip with these numbers in mind. The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it.
    - gruez 1y ago
      >The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it. Are you just describing product segmentation? ie. how the ryzen 5700x and 5800x are basically the same chip, down to the number of enabled cores, except for clocks and power limit ("TDP")?
      - db48x 1y ago
        Yep. The 5800X is a higher bin specifically because it can clock higher than the ones in the 5700X bin. That certainly makes them draw more power, so they give them a higher TDP number too. But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better.
        gruez 1y ago
        >But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better. I don't get it, are you referring to the phenomenon that different workloads have different power consumption (eg. a bunch of AVX512 floating point operations vs a bunch of NOPs), therefore TDP is totally made up? I agree that there's a lot of factors that impact power usage, and CPUs aren't like a space heater where if you let it run at full blast it'll always consume the TDP specified, but that doesn't mean TDP numbers are made up. They still vaguely approximate power usage under some synthetic test conditions, or at the very least is vaguely correlated to some limit of the CPU (eg. PPT limit on AMD platforms).
- kllrnohj 1y ago
  > Couldn't this count as false/misleading advertizing though? For what, exactly? TDP stands for "thermal design power" - nothing in that means peak power or most power. It stopped being meaningful when CPUs learned to vary clock speeds and turbo boost - what is the thermal design target at that point, exactly? Sustained power virus load?
  - einpoklum 1y ago
    > For what, exactly? TDP stands for "thermal design power" The chip is not designed for this rate of power dissipation; and it is not the rate of power dissipation that you can expect to get from the chip.
    - kllrnohj 1y ago
      > The chip is not designed for this rate of power dissipation Says who? AMD advertises the chip as having a base clock of 4.3 GHz over all cores. The 9950X pulls somewhere around 220W at 5ghz all cores and with how power scales, 170W at the advertised 4.3 GHz seems more than plausible. Seems perfectly within reason that the advertised frequency and the advertised TDP are aligned. I wish Anandtech was still around as iirc they did have charts for all this, which nobody else seems to do :/ > and it is not the rate of power dissipation that you can expect to get from the chip. Again, says who? Who's expectations? This is a consumer chip, and the expectations of a consumer chip is not that it spends 100% of its time running prime95 or a similar "power virus" workload. I expect that if I buy this chip while I would have intervals of >170W, I'd also have long periods of much less than 170W. If I have a cooler designed to sustain 170W of cooling, that's going to work out on average just fine as there's thermal mass in the system.
      - einpoklum 1y ago
        > Says who? Says AMD and says Intel, apparently. At the link, there is an official explanation (sort of) how the TDP figure is derived.
aidenn0 1y ago
I have a 65W TDP CPU, and the difference in power draw (measured at the outlet) from idle to full CPU load is over 100W; it seems to just raise the clock until it hist 95C, so if I limit the CPU fan's top speed, the power draw goes down.
- db48x 1y ago
  Yep. Modern CPUs continually adjust their clock multiplier based on what their temperature is doing, plus a few timers. If you have a better cooler then you’ll get more performance out of the same CPU, but at the cost of drawing more power and producing more heat.
bayindirh 1y ago
When I see the term TDP, I remember what I have read in the "Thermal Design Document" of Intel Core2Quad Q6600 and the family it belongs: > The thermal solution bundled with the CPUs is not designed to handle the thermal output when all the cores are utilized 100%. For that kind of load, a different thermal solution is strongly recommended (paraphrased). I never used the stock cooler bundled with the processor, but what kind of dark joke is this?
- deleted 1y ago
  [deleted]
- lofaszvanitt 1y ago
  I always used the stock cooler, because it's quiet and nothing uses the cpu to its fullest :).
- johncolanduoni 1y ago
  Most states of “100% utilization” as you’d see in `top` are not 100% thermal output or even close. Cores waiting for memory accesses count as utilized in the former sense but will not produce as much heat as one that is actually using the ALU etc. That’s why special make-work like Prime95 is used for stress testing overclocking/thermals: it will saturate the cores with enough unblocked arithmetic work to generate more heat than having 1000 browser tabs open does.
  - account42 1y ago
    You're not going to get anywhere near full thermal load with just integer arithmetic either - you need to saturate the floating point units for that.
- cogman10 1y ago
  Man that was a beast of a CPU back in the day. The Conroe Intel era was amazing for the time.
  - keanebean86 1y ago
mrb 1y ago
You are correct. In fact these guys measured a maximum socket power consumption of 240 watt using a 9950X at stock settings, running prime95. So far above the "170 watt" TDP: https://hwbusters.com/cpu/amd-ryzen-9-9950x-cpu-review-performance-thermals-power-analysis/10/ https://hwbusters.com/cpu/amd-ryzen-9-9950x-cpu-review-perfo...
- dcrazy 1y ago
  I don’t understand this argument. If the CPU dissipated an equal number of watts of heat energy as it consumed from the wall, there wouldn’t be any energy left to do actual useful work. Isn’t the extra 100W accounted for by things like changing the state of flip-flops? In other words, mustn’t one consider the entropy reduction of the system as an energy sink?
  - db48x 1y ago
    Nope. Remember that you cannot destroy energy. The energy you use to flip the flip flop still exists, only now it’s just disordered waste heat instead of electricity.
    - dcrazy 1y ago
      Energy cannot be created or destroyed, but it can enter and leave an open system. When I lift a 10kg box 1 meter in the air, I don’t raise its temperature at all, and I only raise mine a tiny bit, yet I have still done work on the box and therefore have imparted it energy. The energy came from food I ate earlier, and was ultimately stored in the box as gravipotential energy. Is this not analogous to storing energy in the EM fields within the CPU?
      - lmm 1y ago
        CPUs don't store nontrivial amounts of energy, and even if storing a 1 was a significantly higher energy level than a 0 (or vice versa) there's no plausible workload that would be causing the CPU to switch significantly more 0s to 1s than 1s to 0s (or vice versa).

by db48x 1y ago

einpoklum 1y ago

Wow, I can't believe how BS this TDP is! I feel like a total idiot! I've always assumed it's sorta-kinda a tight upper bound on power consumption, perhaps with some allowance for "imperfections" in the dissipation properties of the CPU, and that I shouldn't sweat the details. Couldn't this count as false/misleading advertizing though?

vel0city 1y ago
Its pretty insane to see someone say something like: “TDP is about thermal watts, not electrical watts. These are not the same.” Watts are watts. But yeah, TDP means nothing. If you stick plenty of cooling and run the right motherboard board revision your "TDP" can be whatever you want it to be until the thing melts.
- o11c 1y ago
  "TDP is about average watts, not peak watts" would be an honest way of saying it.
  - vel0city 1y ago
    But in the end that's still not actually true in many modern desktop chips. You can take a 65W part, and with a "stock" motherboard firmware, good cooling, and the right workload end up averaging way more than 65W. Or if you have it in a hot room it just might end up using less than 65W. TDP is more of a rough idea of how much power the manufacturer wanted to classify the part as. It ultimately only loosely relates to the actual heat or electrical usage in practice.
gruez 1y ago
It's thermal design power, ie. it's the power that it's designed for, not absolute max.
- db48x 1y ago
  No, they don’t design the chip with these numbers in mind. The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it.
  - gruez 1y ago
    >The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it. Are you just describing product segmentation? ie. how the ryzen 5700x and 5800x are basically the same chip, down to the number of enabled cores, except for clocks and power limit ("TDP")?
    - db48x 1y ago
      Yep. The 5800X is a higher bin specifically because it can clock higher than the ones in the 5700X bin. That certainly makes them draw more power, so they give them a higher TDP number too. But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better.
      - gruez 1y ago
        >But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better. I don't get it, are you referring to the phenomenon that different workloads have different power consumption (eg. a bunch of AVX512 floating point operations vs a bunch of NOPs), therefore TDP is totally made up? I agree that there's a lot of factors that impact power usage, and CPUs aren't like a space heater where if you let it run at full blast it'll always consume the TDP specified, but that doesn't mean TDP numbers are made up. They still vaguely approximate power usage under some synthetic test conditions, or at the very least is vaguely correlated to some limit of the CPU (eg. PPT limit on AMD platforms).
kllrnohj 1y ago
> Couldn't this count as false/misleading advertizing though? For what, exactly? TDP stands for "thermal design power" - nothing in that means peak power or most power. It stopped being meaningful when CPUs learned to vary clock speeds and turbo boost - what is the thermal design target at that point, exactly? Sustained power virus load?
- einpoklum 1y ago
  > For what, exactly? TDP stands for "thermal design power" The chip is not designed for this rate of power dissipation; and it is not the rate of power dissipation that you can expect to get from the chip.
  - kllrnohj 1y ago
    > The chip is not designed for this rate of power dissipation Says who? AMD advertises the chip as having a base clock of 4.3 GHz over all cores. The 9950X pulls somewhere around 220W at 5ghz all cores and with how power scales, 170W at the advertised 4.3 GHz seems more than plausible. Seems perfectly within reason that the advertised frequency and the advertised TDP are aligned. I wish Anandtech was still around as iirc they did have charts for all this, which nobody else seems to do :/ > and it is not the rate of power dissipation that you can expect to get from the chip. Again, says who? Who's expectations? This is a consumer chip, and the expectations of a consumer chip is not that it spends 100% of its time running prime95 or a similar "power virus" workload. I expect that if I buy this chip while I would have intervals of >170W, I'd also have long periods of much less than 170W. If I have a cooler designed to sustain 170W of cooling, that's going to work out on average just fine as there's thermal mass in the system.
    - einpoklum 1y ago
      > Says who? Says AMD and says Intel, apparently. At the link, there is an official explanation (sort of) how the TDP figure is derived.

aidenn0 1y ago

I have a 65W TDP CPU, and the difference in power draw (measured at the outlet) from idle to full CPU load is over 100W; it seems to just raise the clock until it hist 95C, so if I limit the CPU fan's top speed, the power draw goes down.

db48x 1y ago
Yep. Modern CPUs continually adjust their clock multiplier based on what their temperature is doing, plus a few timers. If you have a better cooler then you’ll get more performance out of the same CPU, but at the cost of drawing more power and producing more heat.

bayindirh 1y ago

When I see the term TDP, I remember what I have read in the "Thermal Design Document" of Intel Core2Quad Q6600 and the family it belongs: > The thermal solution bundled with the CPUs is not designed to handle the thermal output when all the cores are utilized 100%. For that kind of load, a different thermal solution is strongly recommended (paraphrased). I never used the stock cooler bundled with the processor, but what kind of dark joke is this?

deleted 1y ago
[deleted]
lofaszvanitt 1y ago
I always used the stock cooler, because it's quiet and nothing uses the cpu to its fullest :).
johncolanduoni 1y ago
Most states of “100% utilization” as you’d see in `top` are not 100% thermal output or even close. Cores waiting for memory accesses count as utilized in the former sense but will not produce as much heat as one that is actually using the ALU etc. That’s why special make-work like Prime95 is used for stress testing overclocking/thermals: it will saturate the cores with enough unblocked arithmetic work to generate more heat than having 1000 browser tabs open does.
- account42 1y ago
  You're not going to get anywhere near full thermal load with just integer arithmetic either - you need to saturate the floating point units for that.
cogman10 1y ago
Man that was a beast of a CPU back in the day. The Conroe Intel era was amazing for the time.
- keanebean86 1y ago

mrb 1y ago

You are correct. In fact these guys measured a maximum socket power consumption of 240 watt using a 9950X at stock settings, running prime95. So far above the "170 watt" TDP: https://hwbusters.com/cpu/amd-ryzen-9-9950x-cpu-review-performance-thermals-power-analysis/10/ https://hwbusters.com/cpu/amd-ryzen-9-9950x-cpu-review-perfo...

dcrazy 1y ago
I don’t understand this argument. If the CPU dissipated an equal number of watts of heat energy as it consumed from the wall, there wouldn’t be any energy left to do actual useful work. Isn’t the extra 100W accounted for by things like changing the state of flip-flops? In other words, mustn’t one consider the entropy reduction of the system as an energy sink?
- db48x 1y ago
  Nope. Remember that you cannot destroy energy. The energy you use to flip the flip flop still exists, only now it’s just disordered waste heat instead of electricity.
  - dcrazy 1y ago
    Energy cannot be created or destroyed, but it can enter and leave an open system. When I lift a 10kg box 1 meter in the air, I don’t raise its temperature at all, and I only raise mine a tiny bit, yet I have still done work on the box and therefore have imparted it energy. The energy came from food I ate earlier, and was ultimately stored in the box as gravipotential energy. Is this not analogous to storing energy in the EM fields within the CPU?
    - lmm 1y ago
      CPUs don't store nontrivial amounts of energy, and even if storing a 1 was a significantly higher energy level than a 0 (or vice versa) there's no plausible workload that would be causing the CPU to switch significantly more 0s to 1s than 1s to 0s (or vice versa).