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My summary is AMD is hurt MUCH less than Intel by lowering the power. One example from the article: Cinebench R23 multithread: Ryzen 7950X 230 -> 125 watts

by sliken 4y ago

My summary is AMD is hurt MUCH less than Intel by lowering the power. One example from the article: Cinebench R23 multithread: Ryzen 7950X 230 -> 125 watts = 95% Ryzen 7950X 230 -> 105 watts = 93% Ryzen 7950X 230 -> 65 watts = 81% Intel I9-13900k 253 watts -> 125 watts = 78% Intel I9-13900k 253 watts -> 105 watts = 72% Intel I9-13900k 253 watts -> 65 watts = 56% Other benchmarks like C-ray show ZERO slowdown going from 230 -> 125 and even 105 watts. Intel drops by 21% for 125 watts and 30% for 105 watts. Personally I'd rather get the 7900X (or non-x) and you'd keep an even larger fraction of the performance within a given power limit. It's pretty clear who has the worse core and has to push harder into high clock/terrible power usage for not much gain curve.

mtlmtlmtlmtl 4y ago
I'm a little dubious of benchmarks that compare only one pair of chips when it comes to details like power efficiency and tweaking. The silicon lottery can make a big difference.
- sliken 4y ago
  Sure. Various forums corroborate the reducing the Ryzen 7000 series at 65 TDP is often a less than 10% decrease in performance. Also keep in mind that "performance mode" on Intel can significantly increase the default 253 watt TDP. Anandtech reviews of the i9-13900k hit 380 watts I believe. So sure there's chip to chip variation, but generally the AMD chips are more power efficient and have much lower penalties for reducing the TDP.
  - inawarminister 4y ago
    Do you know how to undervolt laptop Ryzens? I'm really interested if we can increase the battery life by another 30-40% or so
    - scheme271 4y ago
      The easiest way is to go to the bios or cpu settings and change the precision optimizer so that you have a negative pbo setting. That'll reduce the stock voltage at a given frequency. It'll also potentially speed your chip up since this lets the chip boost to higher frequencies at a given power level. I think the lowest you can go is -30, but try -20 or so and see if your system is stable before trying lower values.
  - mtlmtlmtlmtl 4y ago
    I'm not sure whether I've won the lottery or Intel's software is unreliable. I've been playing around with the 13900K's settings and so far I've managed to get it down to a stable 210W TDP(according to XTU under stress testing. That's with a 0.110V undervolt(likely could do more) and the P-core turbo multipliers tapering down to 50 with all cores active from 57 with 1 core active. I've yet to mess with the E-cores though; could probably shave off some more perf/W still.
    - sagarm 4y ago
      I think managing a 100mV undervolt is pretty common for the 13900K. That's what I have as well, with a power limit of 200W. The penalty in cinebench is only ~5% despite the 20% reduction in power.
- geerlingguy 4y ago
  I just tested my 7900x yesterday and it gets about 95% of the max performance at 105W TDP. The system idles at half the wattage, too—so it's saving a ton of energy not running at the stock 170W TDP. Not sure why AMD didn't go for efficiency crown, especially for non-halo SKUs like the 7950.
  - 0cf8612b2e1e 4y ago
    Have you tested draw from the outlet? I assumed that modern chips could scale down their power usage significantly when idle. Which is to say I thought consumers would rarely ever hit maximum power draw, so I would expect really modest real-world savings. Happy to be proven wrong, because it is a brilliant idea. My machine is wildly oversized for my typical usage, and I could easily take a 10%+ performance haircut and likely would not even notice.
    - trashtester 4y ago
      That's part of the reason they're given such a high TDP by default. The cost of squeezing out the last 5-15% may be worth it if it for short periods of time. But if you use these chips for tasks that max out all cores for several hours per day, it may be better the simply run a chip with more cores and to run those in econ mode. A 7950X@64W may perform as well as a 7900X@200W for such compute tasks, and are probably cheaper over time. And if you use it in your house, they generate less noise, can use a cheaper cooler and doesn't dump so much heat into your room.
      - 0cf8612b2e1e 4y ago
        Thanks for the thoughts. My untested suspicion is that my CPU hits max load for <5% of total use. Meaning lowering max TDP is unlikely to noticeably impact my electrical bill, but it’s such a cheap optimization to enable, why not?

by sliken 4y ago

mtlmtlmtlmtl 4y ago

I'm a little dubious of benchmarks that compare only one pair of chips when it comes to details like power efficiency and tweaking. The silicon lottery can make a big difference.

sliken 4y ago
Sure. Various forums corroborate the reducing the Ryzen 7000 series at 65 TDP is often a less than 10% decrease in performance. Also keep in mind that "performance mode" on Intel can significantly increase the default 253 watt TDP. Anandtech reviews of the i9-13900k hit 380 watts I believe. So sure there's chip to chip variation, but generally the AMD chips are more power efficient and have much lower penalties for reducing the TDP.
- inawarminister 4y ago
  Do you know how to undervolt laptop Ryzens? I'm really interested if we can increase the battery life by another 30-40% or so
  - scheme271 4y ago
    The easiest way is to go to the bios or cpu settings and change the precision optimizer so that you have a negative pbo setting. That'll reduce the stock voltage at a given frequency. It'll also potentially speed your chip up since this lets the chip boost to higher frequencies at a given power level. I think the lowest you can go is -30, but try -20 or so and see if your system is stable before trying lower values.
- mtlmtlmtlmtl 4y ago
  I'm not sure whether I've won the lottery or Intel's software is unreliable. I've been playing around with the 13900K's settings and so far I've managed to get it down to a stable 210W TDP(according to XTU under stress testing. That's with a 0.110V undervolt(likely could do more) and the P-core turbo multipliers tapering down to 50 with all cores active from 57 with 1 core active. I've yet to mess with the E-cores though; could probably shave off some more perf/W still.
  - sagarm 4y ago
    I think managing a 100mV undervolt is pretty common for the 13900K. That's what I have as well, with a power limit of 200W. The penalty in cinebench is only ~5% despite the 20% reduction in power.
geerlingguy 4y ago
I just tested my 7900x yesterday and it gets about 95% of the max performance at 105W TDP. The system idles at half the wattage, too—so it's saving a ton of energy not running at the stock 170W TDP. Not sure why AMD didn't go for efficiency crown, especially for non-halo SKUs like the 7950.
- 0cf8612b2e1e 4y ago
  Have you tested draw from the outlet? I assumed that modern chips could scale down their power usage significantly when idle. Which is to say I thought consumers would rarely ever hit maximum power draw, so I would expect really modest real-world savings. Happy to be proven wrong, because it is a brilliant idea. My machine is wildly oversized for my typical usage, and I could easily take a 10%+ performance haircut and likely would not even notice.
  - trashtester 4y ago
    That's part of the reason they're given such a high TDP by default. The cost of squeezing out the last 5-15% may be worth it if it for short periods of time. But if you use these chips for tasks that max out all cores for several hours per day, it may be better the simply run a chip with more cores and to run those in econ mode. A 7950X@64W may perform as well as a 7900X@200W for such compute tasks, and are probably cheaper over time. And if you use it in your house, they generate less noise, can use a cheaper cooler and doesn't dump so much heat into your room.
    - 0cf8612b2e1e 4y ago
      Thanks for the thoughts. My untested suspicion is that my CPU hits max load for <5% of total use. Meaning lowering max TDP is unlikely to noticeably impact my electrical bill, but it’s such a cheap optimization to enable, why not?