What does Turbo Time Limit exactly mean? How often can a CPU go into turbo mode per timeslot?

[Rexon112]

I understand that short power PL2 allows the processor to run at higher watt. I also understand what clamp means.

However, what does the turbo time limit exactly mean? Is there a "time guard space" between how often a turbo can occur? How often can a CPU go turbo mode per timeslot?

I have done a benchmarking experiment because I didn't found much information about a possible time guard space. PL1=15[W], PL2=25[W], time=10. The CPU went full usage mode with prime95, that is it used the most possible wattage. Before it was in idle.

My observations were the following: When the CPU hits the PL1 limit from below, that is power consumption goes up from 1[W] to PL1[W], it gets a turbo time space for 10. That happens right after I started the benchmark. Afterwards, the PL1 limit is applied again. If the power consumption is still as high as PL1, which it is because of the stress test, processor won't get another turbo. It only gets another PL2 turbo if the wattage goes down significantly below the PL1 limit, for example if I stop and restart the benchmark.

My conclusion is that the PL1 and PL2 limits work like a hysteresis. You reach the PL1 limit from below, you get a turbo. You reach the PL1 limit from above, that is you just were in a PL2 turbo and the CPU still needs to be throttled by PL1, you won't get another turbo. You need to go down way lower than the PL1 limit until the PL1 doesn't throttle anymore. Then you get another PL2 turbo. There doesn't seem to be any time guard space between two PL2 turbos though, like a "a turbo can only occur after the previous one ended for 5 seconds".

Does this make sense?

 

[unclewebb]

like a "a turbo can only occur after the previous one ended for 5 seconds".

I have never come across any publicly available documentation from Intel that explains their turbo boost formula. The exact formula has likely changed over the years and might also change each generation depending on the CPU model.

An Intel engineer once compared turbo boost to water in a bath tub. Water continuously flows into the tub and a drain hole at the bottom allows water to flow out of the tub. When there is water in the tub, the CPU can use maximum turbo boost. This is sort of equivalent to PL2.

Running a demanding app is like opening up a large drain hole in the bottom of the tub. The water will drain out very quickly when running a stress test like Prime95 Small FFTs compared to when running most games. When the turbo boost tub is empty, this will force the CPU to slow down. It will do this to reduce power consumption from the PL2 power limit to the PL1 power limit.

The PL1 power limit is the long term power limit. A CPU is designed to run indefinitely at the long term PL1 turbo power limit. The amount of turbo boost available will continuously vary so long term the CPU does not exceed the PL1 power limit. When the Clamp option is checked, the CPU will reduce its speed below the base frequency if necessary. When the Clamp option is not checked, the CPU will only reduce its speed during power limit throttling as low as the base frequency.

The turbo time limit is just an approximation of how long the CPU can run at PL2 before being reduced to the PL1 power limit. Prime95 will drain the turbo boost tub much quicker compared to a light load stress test.

For my desktop computer, I set both turbo power limits sky high. That ensures maximum performance. Power limit throttling is not necessary if you have good cooling.