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CPU power scaling
AnandTech has now done the CPU review that I wanted to see:
https://www.anandtech.com/show/17641/lighter-touch-cpu-power-scaling-13900k-7950x
The idea is that you take AMD's and Intel's top end consumer CPUs, give them a lower power limit, and see what happens. Obviously, a lower power limit means lower clock speeds and lower performance. But the big question is, how much lower?
In some tests, the Ryzen 9 7950X at 65 W beats a Core i9-13900K at 125 W. That even happens sometimes when the latter CPU wins outright if you take off the power limits. Reducing the power limit on the AMD CPU throttles back performance a lot less than on the Intel CPU.
Probably not coincidentally, reducing the power limit on the AMD CPU throttles back real-world power usage a lot less than on the Intel CPU. At any given set wattage, the AMD CPU is willing to burn quite a bit more power than the Intel one. What I think is going on here is that AMD is regarding the set power as their TDP, but allows turbo to use 35% more power than the TDP. The Intel CPU also goes over the stated power limit, but by a lot less than the AMD one. Is it really so impressive that the AMD CPU at 105 W is faster than the Intel CPU at 125 W if the AMD CPU is also using more power in the real world in spite of the lower nominal power limit?
But I also think that it's interesting what happens if they take the power limits off. The AMD CPU that nominally can go up to 230 W actually stops at 215 W. The Intel CPU with a PL2 power of 253 W ends up burning over 330 W. The difference between 230 W and 253 W isn't that much, but the difference between 215 W and 330 W is quite a lot.
Ultimately, if you want the most performance that you can get in a given power envelope, AMD wins that pretty handily. That shouldn't be surprising, as they're on a better process node. But if you do want to buy an AMD CPU and throttle back the power, you have to set the nominal power limit to about 3/4 of what you want an AMD CPU to actually use in the real world.
The other interesting takeaway is that in the gaming benchmarks, throttling back CPU power basically didn't matter, even if you set the CPUs all the way down to 35 W. They only tested two games, but still, most games don't really push high end CPUs very hard.
https://www.anandtech.com/show/17641/lighter-touch-cpu-power-scaling-13900k-7950x
The idea is that you take AMD's and Intel's top end consumer CPUs, give them a lower power limit, and see what happens. Obviously, a lower power limit means lower clock speeds and lower performance. But the big question is, how much lower?
In some tests, the Ryzen 9 7950X at 65 W beats a Core i9-13900K at 125 W. That even happens sometimes when the latter CPU wins outright if you take off the power limits. Reducing the power limit on the AMD CPU throttles back performance a lot less than on the Intel CPU.
Probably not coincidentally, reducing the power limit on the AMD CPU throttles back real-world power usage a lot less than on the Intel CPU. At any given set wattage, the AMD CPU is willing to burn quite a bit more power than the Intel one. What I think is going on here is that AMD is regarding the set power as their TDP, but allows turbo to use 35% more power than the TDP. The Intel CPU also goes over the stated power limit, but by a lot less than the AMD one. Is it really so impressive that the AMD CPU at 105 W is faster than the Intel CPU at 125 W if the AMD CPU is also using more power in the real world in spite of the lower nominal power limit?
But I also think that it's interesting what happens if they take the power limits off. The AMD CPU that nominally can go up to 230 W actually stops at 215 W. The Intel CPU with a PL2 power of 253 W ends up burning over 330 W. The difference between 230 W and 253 W isn't that much, but the difference between 215 W and 330 W is quite a lot.
Ultimately, if you want the most performance that you can get in a given power envelope, AMD wins that pretty handily. That shouldn't be surprising, as they're on a better process node. But if you do want to buy an AMD CPU and throttle back the power, you have to set the nominal power limit to about 3/4 of what you want an AMD CPU to actually use in the real world.
The other interesting takeaway is that in the gaming benchmarks, throttling back CPU power basically didn't matter, even if you set the CPUs all the way down to 35 W. They only tested two games, but still, most games don't really push high end CPUs very hard.
Comments
The AMD CPU that nominally can go up to 230 W actually stops at 215 W. .... The difference between 230 W and 253 W isn't that much, ...
Maybe the second number is correct? Not sure.
Power would be Watts, which is correct. But 105 < 125, so it can't be that power usage is both lower and higher at the same time. I think here you mean AMD uses more ~energy~ despite having a lower ~power~ limit -- it can have a lower peak power draw, but use more energy (normally measured in kWh, but that would be somewhat of an impractical measurement here) because it throttles back less.
Just nitpicking. Good read overall. The power vs energy thing is somewhat eye opening, I would not have expected that.
On the second point, the AMD CPU with a nominal power limit of 105 W is generally faster than the Intel CPU with a nominal power limit of 125 W, but at those settings, the AMD CPU was also measured as using a little more power than the Intel one, in spite of the lower nominal power limit. Realizing that is essential in order to understand the performance graphs at various power limits.