How to Understand Intel CPU’s “Turbo Boost Power Time Window”?

This is the official description of the setting item, “Turbo Boost Power Time Window,” from XTU (Intel® Extreme Tuning Utility):

The Time window over which the average CPU core power must be below the Turbo Boost Power Max.(PL1 Time)

This setting item is not related to “Turbo Boost Short Power Max” for two reasons: 1) After disabling “Turbo Boost Short Power Max,” this setting item can still be adjusted, but “Turbo Boost Short Max” can no longer be set; 2) The abbreviation of this setting item is PL1 Time, not PL2 Time, indicating that it is only related to “Turbo Boost Power Max.”

On my Intel i7-8565U, this setting item can be set between 0.25s and 96s, but not 0s.

How should we understand this time window? Based on my tests, when I set this time window to 96s and the “Turbo Boost Power Max” to 8W, and ran XTU’s Benchmark, the TDP initially maintained a power of about 19W for approximately seven seconds, then dropped to 8W, and even dipped to 4-5W at one point, before fluctuating around 8W. When I set the time window to 0.25s, the TDP fluctuated around 8W from the beginning, with relatively smaller variations.

Thus, the “Turbo Boost Power Time Window” is essentially a tolerance level for the CPU to exceed the “Turbo Boost Power Max.” The shorter the power time window, the less likely the CPU will exceed that power; conversely, the longer the power time window, the more likely the CPU will exceed that power.

For instance, when the time window is set to the lowest value of 0.25s, it means that for every 0.25s cycle, the average TDP of the CPU cannot exceed the “Turbo Boost Power Max” you have set. In such a short time cycle, you won’t experience the CPU exceeding the “Turbo Boost Power Max” at all. If the time window is set to the highest value of 96s, it means that the average TDP of the CPU cannot exceed the “Turbo Boost Power Max” for each 96s cycle. This allows the CPU to run at high power for a few seconds before falling back. Since the average power consumption in each 96s cycle cannot be higher than the “Turbo Boost Power Max,” the CPU must sometimes operate below that power level.

In summary, the longer the time window, the more the CPU’s TDP fluctuates around the “Turbo Boost Power Max,” and the shorter the time window, the less the CPU’s TDP fluctuates around the “Turbo Boost Power Max.”