Question Why Does Cinebench Score Reduce in Progress?

[steve489]

I've built a new PC using an i7-13700K CPU and Asus Z790 motherboard. The BIOS is set to defaults except that I set a maximum CPU temperature of 85C, a Short Duration Package Power Level 200W and Long Duration Package Power Level 125W.

On running Cinebench R23 I get a decent benchmark score c. 29000 and see the thermal limit 85C applied. After a minute or so the score reduces about 10% and the CPU temperature drops under 85C. What's going on here to limit performance?

 

[rgd1101]

time. long/short duration

 

[hotaru.hino]

I'm not too privy to Intel's boosting behavior, but it looks like it use PL2 until the CPU hits the temperature limit, at which point the CPU believes the cooling system can't actually keep the CPU at the temperature limit and drops to PL1 and it won't try PL2 until some "reset" point.

 

[uWebb429]

What's going on here to limit performance?

The long term 125W PL1 turbo power limit is not enough power to run Cinebench at maximum speed. Your settings are telling the CPU to slow down during any long term test so it does not exceed 125W. Most enthusiasts set both turbo power limits to the max, 4095W. No more power limit throttling.

looks like it use PL2 until the CPU hits the temperature limit

The temperature of the CPU and the turbo power limits have nothing to do with each other. The turbo power limits and the turbo time limit controls whether turbo boost is used or not. Full turbo boost is available even when the CPU temperature is on the edge of thermal throttling. This usually starts at 100C.

There is no need to lower this to 85C. Intel CPUs can run reliably at up to 100C. They have been using this standard throttling temperature for the last 15 years.

 

[hotaru.hino]

The temperature of the CPU and the turbo power limits have nothing to do with each other. The turbo power limits and the turbo time limit controls whether turbo boost is used or not. Full turbo boost is available even when the CPU temperature is on the edge of thermal throttling. This usually starts at 100C.

From what I gather, since 12th gen, the PL2 time for unlocked processors is now infinite by default. In addition, a lot of higher end motherboards max out the PL2 and tau values anyway.

Maybe it sticks at PL2 infinitely regardless if it hits the temperature limit, but I haven't seen anyone post a power consumption over time graph for the 13900K like I've seen with Intel's previous CPUs.

 

[steve489]

Thanks for the above replies. I've now set those power limits back to Auto but kept the 85C temperature limit resulting in a 2% improvement in the Cinebench score. What is realistic maximum CPU temperature to set using my Noctua NH-D14 cooler?

 

[hotaru.hino]

Thanks for the above replies. I've now set those power limits back to Auto but kept the 85C temperature limit resulting in a 2% improvement in the Cinebench score. What is realistic maximum CPU temperature to set using my Noctua NH-D14 cooler?

Intel's CPUs since whenever are designed to hit the temperature limit first. So setting a lower temperature limit will cause a performance drop. Also note that when you see the CPU temperature report from some app, it's likely not the entire processor.

So there's no such thing as a "realistic maximum." Only a "whatever helps you sleep at night" temperature.